Kirk Key Scheme Book

APPLICATION SCHEME BOOK
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APPLICATION SCHEMES - Introduction
In order to lay out complicated interlock schemes, it is necessary to understand the simplest applications. On this page, the basic concepts of
interlocking are outlined and discussed.
Interlocking a Single Unit in One Position Interlocking Two Units in Two Positions
If it is desired to secure a device in the open position, an interlock is The other method for locking in both the open and closed positions
used as in Fig. 1. The possession of the key indicates requires two interlocks as shown in Fig. 4. Possession of key A-1 indicates
that the device is locked open. Possession of key A-2 indicates that
the device is locked closed. The device is shown normally open;
therefore, key A-1 is free and the L-O interlock bolt is extended into its
recess provided in the movable member while key A-2 is held and the
A1 A-1 E A1 A-1 E L-C interlock bolt is withdrawn. To close the device, insert key A-1 in the
L-O lock and turn to withdraw bolt of L-O interlock, which permits the
L-O L-C device to be operated. Now the device can be moved to the closed
Fig. 1 Fig. 2 position. Key A-2 can be turned to extend the bolt of the L-C interlock
into its recess, which locks the device in the closed position.
that the device is in the open position and is locked by the extension
of the interlock bolt. When the key is inserted in the lock and turned to
withdraw the interlock bolt, the device is free to operate to the closed
position and the key is held in the lock. E E
A 1 A-1 A2
L-O L-C
When a device is to be locked only in the closed position an interlock is
used as shown in Fig. 2. The possession of the key indicates that the Fig. 4.
device is locked in the closed position, as the interlock bolt has been This releases Key A-2 from the L-C interlock. Meanwhile, key A-1 is held
extended to remove the key. When the key is inserted in the lock and in the L-O interlock since its withdrawn locking bolt cannot be
turned to withdraw the interlock bolt, the device is free to operate to extended.
the open position and the key is held in the lock.
This method is used more often than the single two-position interlock
Interlocking a Single Unit in Two Positions shown in Fig. 3, due to its adaptability to sequence operations. Also,
the possession of key A-1 or A-2 indicates that the device is locked
Two methods are used in interlocking a device in both open and open or locked closed, respectively.
closed position. The first method requires only one interlock as shown in
Fig. 3. The interlock bolt is extended in both the open and closed Sequence Interlocking
positions. This is accomplished with two recesses in the device that is
being interlocked - each coinciding with the locking bolt in one With the fundamentals developed above, it is quite simple to extend
position. the application to the interlocking of two or more devices in a desired
sequence.
A B
A 1 A-1 E
A-1 E A-1 E
A 1
L-O-C L-O L-O
Fig. 3 Fig. 5
Two devices are shown in Fig. 5. In operation they are not closed at
The possession of the key indicates that the interlock bolt is extended
the same time. With the interlocks arranged as shown, only one key is
and that the device is locked either in the open or closed position.
required in the interlocking system. Both devices are shown open;
Furthermore, the device cannot be operated until the key is inserted
therefore, the key is free. To close any one device, the key is inserted
and turned in the lock to withdraw the locking bolt. The key cannot be
and turned in that particular lock to withdraw the interlock bolt. The key
removed from the lock in an intermediate position, but in the fully
is held in this lock until the device is again locked open. This simple
open or closed positions only. However, in this application, possession
interlocking sequence lends itself to a multitude of applications. The
of the key gives no indication as to whether the device is locked
procedure is the same for two devices, neither of which is to be
closed or open.
opened at the same time.
Legend\Symbols
KIRK KIRK
Access door interlock
Device normally open.
(Detachable latch)
Type D, DM or DY.
Device normally closed. Interlock with
auxiliary switch,
Direction of key transfer. KIRK
2 make - 2 break,
Access door interlock Type SS
Multi-cylinder
A-1, A-2, A-3 Key interchange number. (Detachable latch)
Type D or DM. KIRK
KIRK
Interlock with key held.

Device in position as shown. KIRK
Transfer interlock, Type T. Interlock with

KIRK
auxiliary switch,
Interlock with key removed. T 3 make - 3 break,
Device in position as
Type SSS
shown.
KIRK
KIRK
KIRK
Interlock used to lock Transfer interlock, Type T.
device open. 3 cylinder
L-O (with key removed) Interlock with
auxiliary switch
T
KIRK Type K
Interlock used to lock
KIRK
device open.
L-O
(with key held) KIRK
Key released after time delay.

KIRK
Interlock used to lock Transfer interlock, Type T. Time-delay key release unit
TM
device closed. 5 cylinder
L-C (with key removed) Initiating lock.
KIRK
Interlock used to lock
T
device closed.
L-C (with key held) Solenoid key release unit. Key
Padlock released when solenoid is E,
KIRK KIRK
Type P KIRK energized.
Interlock used to lock device
open and closed.
L-O-C
E
KIRK
KIRK Key Interchange number

A3 (showing key held).
Two key
Multi-lock interlock. Solenoid key release unit. Key
released when solenoid is E,
KIRK
energized.
KIRK
Interlock with Initiating key

KIRK auxiliary switch,
Interlock with Key released when
1 make - 1 break,
an apartment lock. solenoid is energized.
(Accepts one of two keys) Type S
E
E E
Key Removable Positions
A-2 A- 1
The E or W next to the interlock symbol indicates the position of the interlock bolt when the key is removable, E =
L-C A3
W
Extended, W = Withdrawn.
L-O For more information regarding key removable positions please reference the technical paper How an Individual
Key Interlock Operates on our website (Click on ''Customer Portal", "Downloads", and "Manuals & Technical Papers" then
click on How an Individual Key Interlock Operates). Refer also to the Available Options on the interlock data sheets
and to columns 8 and 9 on either Interlock Ordering Guide (Brass or 316 Stainless).
Table Of Contents
Purpose of Interlocking
Scheme# Function
Switch and Breaker
Scheme #1 Prevents opening of switch when breaker is closed.
Scheme #2 Prevents operation of switch when breaker is closed. Permits re-closing the breaker for servicing when switch is locked open.
Scheme #3 Prevents operation of switch when breaker is closed. Circuit cannot be cleared until proper supervisory key is obtained.
Grounding Switch with Main Switch

Scheme #4 Prevents closing of grounding switch when main switch is closed, and vice versa.
Isolating Switches and Breaker

Scheme #5 Prevents operation of disconnect when breaker is closed. Prevents opening fuse compartment door when disconnect is closed.
Scheme #6 Prevents operation of disconnect when any or all of a group of breakers are closed. Operates through transfer interlock, no sequence is
required for breaker closing.
Scheme #7 Prevents operation of disconnect when any or all of a group of breakers are closed. Breakers operated in prearranged sequence.
Scheme #8 Prevents operation of disconnects when breaker is closed. Permits servicing of breaker when disconnects are locked open.
Scheme #9 Prevents operation of disconnects when breaker is closed, and prevents access to breaker compartment with disconnects closed.
Isolating Switches and Breaker or Regulator with By-Pass Switch

Scheme #10 Prevents operation of breaker disconnects and by-pass disconnect under load. Provides for closing of by-pass disconnect before
breaker circuit is opened, or permits circuit breaker to be opened with by-pass disconnect remaining open.
Scheme #10A Prevents operation of voltage regulator disconnects and by-pass disconnect under load. Permits by-pass disconnect to operate only
when regulator is in neutral position. Permits isolating regulator for servicing.
Prevent Paralleling of Lines

Scheme #11 Prevents paralleling of two lines - single load, fed from either source.
Scheme #12 Prevents paralleling of two lines - single load, fed from either source - breaker on load side.
Scheme #13 Prevents paralleling of two lines - two loads, fed from either source (one tie breaker)
Scheme #14 Prevents paralleling of two lines - two loads, fed from either source (one tie breaker). Prevents operation of switch when breaker
is closed (on either source).
Scheme #15 Prevents paralleling of two lines - two loads fed from either source (one tie breaker). Prevents operation (open or closed) of
disconnect when breaker is closed (on either source). Prevents access to fuses when disconnects and breakers are closed.
Scheme #16 Prevents paralleling of three lines - three loads, fed from any source (two tie breakers).
Scheme #17 Prevents paralleling of four lines - four loads fed from any source (three tie breakers)
Scheme #17A Prevents paralleling of four lines - four loads fed from any source (three tie breakers). Also prevents opening of rear access doors when
breakers are energized.
Scheme #18 Prevents paralleling of three lines - three loads fed from any source (three tie breakers).
Scheme #19 Prevents paralleling of four lines - four leads fed from any source (four tie breakers).
Scheme #20 Prevents paralleling of three power sources through a common tie bus not normally in service. Permits feeding any load bus from
a second power source through the tie bus. Permits one power source to supply all three load buses through the tie bus.
Scheme #21 Prevents paralleling three power sources through a common tie bus not normally in service. Permits feeding any load bus from a
second power source through the tie bus only when authorized by a supervisor. Permits one power source to supply all three load
buses through the tie bus only when authorized by a supervisor.
Scheme #22 Prevents paralleling two incoming primary sources through primary tie bus disconnect. Prevents operation (open or closed) of the
disconnects under load. Permits one power source to supply both loads through tie bus.
Scheme #23 Prevents paralleling of two incoming primary sources through the primary tie bus disconnect or secondary tie bus breaker. Prevents
operation (open or closed) of disconnects under load. Permits one power source to supply both loads through either the primary or
secondary tie bus.
Scheme #24 Prevents paralleling of two incoming primary sources. Prevents operation (open or closed) of disconnects under load. Permits the
isolating of breakers for servicing. Permits one power source to supply both loads through tie bus.
Interrupter Switch
Scheme #25 Prevents opening fuse compartment door when the interrupter switch is closed. Prevents closing interrupter switch until fuse
compartment door is locked closed.
Scheme #26 Prevents operation (open or closed) of interrupter switch when breaker is closed. Permits the breaker to be serviced and operated
while the interrupter switch is locked open.
Table of Contents Continued Next Page

Table Of Contents
Scheme# Function
Interrupter Switch
Scheme #27 Prevents operation (open or closed) of interrupter switch when breaker is closed. Prevents opening fuse compartment door when
interrupter switch is closed. Prevents closing interrupter switch until fuse compartment door is locked closed. Permits the breaker to
be serviced and operated while the interrupter switch is locked open.
Scheme #28 Prevents dropping load when shifting from one source to the other. Prevents opening both interrupter switches at the same time.
Permits both interrupter switches to be closed at the same time.
Scheme #29 Prevents paralleling two lines - requires dropping load when shifting from one source to the other. Prevents closing both interrupter
switches at the same time. Permits both interrupter switches to be opened at the same time.
Scheme #30 Prevents paralleling two lines - requires dropping load when shifting from one source to the other. Prevents closing both interrupter
switches at the same time. Permits both interrupter switches to be open at the same time. Prevents operation (open or closed) of
either interrupter switch when breaker is closed. Permits the breaker to be serviced and operated while both interrupter switches are
locked open.
Scheme #31 Prevents operation (closed, open or closed) of a three position interrupter switch when the breaker is closed. Permits the breaker to
be serviced and operated while the interrupter switch is locked open.
Scheme #32 Prevents operation (closed, open or closed) of a three position interrupter switch when the breaker is closed. Prevents opening fuse
compartment door when the interrupter switch is closed. Prevents closing interrupter switch until fuse compartment door is locked
closed. Permits the breaker to be serviced and operated while the interrupter switch is locked open.
Motor or Machinery Guard

Scheme #33 Prevents opening of guard when motor circuit is closed. Guard may be a door or fence gate that prevents access to moving parts, belts,
cutters, or any dangerous equipment.
Motor or Machinery Guard with Time Delay

Scheme #34 Prevents opening of guard (or door) for a predetermined time after removal of power (from motor, centrifuge, condensers, etc.)
Breakers and Generators

Scheme #35 Prevents paralleling of two lines - two loads, fed from either source (one tie breaker). Allows switching loads to a generator.
Scheme #35A Prevents closing generator breaker when main breaker is closed.
Scheme #36 Prevents paralleling of two lines - two loads, fed from either source (one tie breaker). Allows switching loads to two generators.
Capacitor Bank Access

Scheme #37 Prevents access to capacitor bank enclosure until capacitors have been grounded and discharged.
Scheme #38 Prevents access to capacitor bank enclosure until capacitors have been grounded and discharged - utilizing a Time Delay Key Release
Unit (TDKRU).
Uninterrupted Power Sources

Scheme #39 Prevents improper maintenance bypass of UPS equipment.
Scheme #40 Prevents improper maintenance bypass of UPS equipment.
Precipitator Access
Scheme #41 Prevents access to an electrostatic precipitator, scrubber, or baghouse until all power supplies have been de-energized and properly
grounded.
Scheme #42 To allow operation of dual output transformer rectifiers with one field removed from service and to prevent opening any access doors of
an electrostatic precipitator until all power supplies are de-energized and properly grounded.
Scheme #42A To allow operation of dual output transformer rectifiers with one field removed from service and to prevent opening any access doors of
Scheme #42B To allow operation of dual output transformer rectifiers with one field removed from service and to prevent opening any access doors of
Table of Contents Continued Next Page

Table Of Contents
Scheme# Function
Rectifier Access
Scheme #43 Prevents opening any rectifier enclosure door while the rectifier is operating.
Scheme #43A Prevents opening any rectifier enclosure door while the rectifier is operating.
Scheme #44 Prevents opening any rectifier enclosure door while the rectifier is operating.
Scheme #45 Prevents opening any rectifier enclosure door while the rectifier is operating and prevents opening the negative disconnect
switch under load.
Scheme #45A Prevents opening any rectifier enclosure door while the rectifier is operating and prevents opening the negative disconnect
switch under load.
Scheme 1 Scheme 3
To prevent opening of switch A when breaker B is closed. To prevent operation of switch A when breaker B is closed. Circuit
cannot be cleared until proper supervisory key is obtained.
A
B
A
B
A-1 E A 1 E
L-C L-O
W A-2 A 2
SUPERVISORY
Switch A and breaker B are in closed position. Key A-1 is held in breaker A-1 E A 1 E KEY
B interlock.
L-O-C L-O
1. Open breaker.
2. Turn key A-1 in L-O interlock on breaker B to lock open. Key A-
1 is now free.
3. Insert key A-1 in L-C interlock on switch A and turn to unlock.
4. Open switch A. Key A-1 is now held. Breaker B and switch A shown closed. Key A-1 held in breaker interlock.
Key A-2 retained by supervisor.
Reverse sequence to restore service.
1. Obtain key A-2 from supervisor.

2. Open breaker.
Scheme 2 3. Insert key A-2 in L-O interlock on breaker B and turn key A-1 to
lock open. key A-2 is now held and key A-1 is free.
4. Insert key A-1 in L-O-C interlock on switch A and turn to
To prevent operation of switch A when breaker B is closed. Permits re- unlock.
closing of breaker for servicing when switch is locked open. 5. Open switch A.
6. Turn key A-1 in L-O-C interlock on switch A to lock open. Key
A A-1 is now free.
7. Return key A-1 to breaker interlock and unlock for operation
B during servicing period.

A-1 E A 1 E
L-O-C L-O Scheme 4

To prevent closing of grounding switch B when main switch A is closed,
and vice versa.
A
B A
A-1 E A 1
E
L-O-C L-O B
A 1 E A-1 E
Switch A and breaker B are in closed position. Key A-1 is held in breaker
L-O L-O
B interlock.
1. Open breaker.
2. Turn key A-1 in L-O interlock on breaker B to lock open. Key A- Main switch A shown closed and grounding switch B shown open. Key
1 is now free. A-1 is held in main switch interlock.
3. Insert key A-1 in L-O-C interlock on switch A and turn to
unlock. 1. Open main switch A.
4. Open switch A. Key A-1 is now held. 2. Turn key A-1 in L-O interlock on main switch A to lock open.
5. Turn key A-1 in L-O-C interlock on switch A to lock open. Key Key A-1 is now free.
A-1 is now free. 3. Insert Key A-1 in L-O interlock on grounding switch B and turn
6. Return Key A-1 to breaker interlock and unlock for operation to unlock. Key A-1 is now held.
during servicing period. 4. Close grounding switch B.
Reverse sequence to restore service. Reverse sequence to restore service.

Scheme 5
To prevent operation of disconnect switch A when breaker B is closed. To service breaker:
To prevent opening fuse compartment door when the disconnect 1. Open breaker.
switch A is closed. 2. Turn key A-1 in L-O interlock on breaker to lock breaker open.
Key A-1 is now free.
3. Insert key A-1 in L-O-C interlock on disconnecting switch and
turn to unlock. Key A-1 is now held.
A 4. Open disconnect.
5. Turn key A-1 in L-O-C interlock on disconnect switch to lock
B open. Key A-1 is now free.
of breaker during servicing.
E E E E Reverse sequence to restore service.
A-1 A2 A-2 A 1
To open fuse compartment door:
L-O-C L-O L-C L-O
1. Proceed from normal position with operations as in 1
through 4 above.
2. Turn key A-2 in L-O interlock on disconnect switch to lock
open. Key A-2 is now free.
3. Insert key A-2 in L-C interlock on fuse compartment door
and turn to unlock. Key A-2 is now held.
Breaker, fuse compartment door and disconnect switch are shown in 4. Open fuse compartment door.
closed positions. Key A-1 is held in breaker interlock and key A-2 is held
in disconnect interlock. Reverse sequence to restore service.
Scheme 6
To prevent operation of disconnect switch A when breakers B, C, D and Disconnect A and breakers B, C, D and E are shown in closed position.
E are closed. Breakers may be opened in any sequence. Key A-1 is held in transfer interlock. Keys A-2, A-3, A-4 and A-5 are held
in interlocks on breaker B, C, D and E.
NOTE: Electrical circuit is equivalent of Scheme 7.
1. Open breakers B, C, D and E.
W A- 5
2. Turn key in L-O interlock on each breaker B, C, D and E to
A E lock breakers open. Keys A-2, A-3, A-4 and A-5 are now free.
A-1
W A-4 3. Insert keys A-2, A-3, A-4 and A-5 in transfer interlock.
L-O-C
W A-3
4. Turn key A-1 in transfer interlock. Key A-1 is now free. Keys A-
2, A-3, A-4 and A-5 are now held.
W A-2 5. Insert key A-1 in L-O-C interlock on disconnect A and turn to
unlock. Key A-1 is now held.
A 1 E
6. Open disconnect A.
T
7. Turn key A-1 in L-O-C interlock on disconnect A to lock open.
8. Insert key A-1 in transfer interlock and turn. Key A-1 is now
held, Keys A-2, A-3, A-4 and A-5 are now free.
B C D E 9. Return keys A-2, A-3, A-4 and A-5, as desired, to breaker
E E E E
A2 A3 A4 A5 interlocks and unlock for operation during servicing.
L-O L-O L-O L-O
Scheme 7 Scheme 8
To prevent operation of disconnect switch A when breakers B, C, D and To prevent operation of disconnects A and B when breaker C is
E are closed. Breakers must be opened in pre-arranged sequence. closed. To permit servicing of breaker when disconnects are locked
open.
NOTE: Electrical circuit is equivalent of Scheme 6.
A
E
A B
A-1 A5
L-O-C
SUPERVISORY C
KEY
E E E E E
A2 A-1 A 1 A 1 A-2
B W C W D W E W
A-2 A-3 A-4 A-5 L-O L-C L-O L-O L-C
A 1 A2 A3 A4
L-O E L-O E L-O

E L-O
E
Disconnect A and breakers B, C, D and E are shown in closed position. Breaker C and disconnects A and B are shown closed. One key A-1 is
Key A-1 is held in breaker B interlock, key A-2 is held in breaker C held in breaker L-O interlock and the other key A-1 is held in L-O
interlock, key A-3 is held in breaker D interlock and key A-4 is held in interlock on disconnect B. Key A-2 is held in L-O interlock
breaker E interlock. Key A-5 is held free in breaker E interlock or is on disconnect A.
retained by supervisor.
1. Open breaker.
1. Obtain key A-5 from supervisor. 2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
2. Open breaker E. is now free.
3. Insert key A-5 in L-O interlock on breaker E and turn key A-4 to 3. Insert key A-1 in L-C interlock on disconnect A and turn to
lock open. Key A-5 is now held. Key A-4 is now free. unlock. Key A-1 is now held.
4. Open breaker D. 4. Open disconnect A.
5. Insert key A-4 in L-O interlock on breaker D and turn key A-3 to 5. Turn key A-2 in L-O interlock on disconnect A to lock open.
lock open. key A-4 is now held. key A-3 is now free. Key A-2 is now free.
6. Open breaker C. 6. Insert key A-2 in L-C interlock on disconnect B and turn to
7. Insert key A-3 in L-O interlock on breaker C and turn key A-2 to unlock. Key A-2 is now held.
lock open. Key A-3 is now held. Key A-2 is now free. 7. Open disconnect B.
8. Open breaker B. 8. Turn key A-1 in L-O interlock on disconnect B to lock open.
9. Insert key A-2 in L-O interlock on breaker B and turn key A-1 to Key A-1 is now free.
lock open. Key A-2 is now held. Key A-1 is now free. 9. Insert key A-1 in breaker L-O interlock and turn to unlock for
10. Insert key A-1 in L-O-C interlock on disconnect A and turn to operation during servicing.
11. Open disconnect A. Reverse sequence to restore service.
13. Insert key A-1 in L-O interlock on breaker B and turn to unlock.
Key A-1 is now held and key A-2 is now free.
14. Breaker B may now be operated for servicing.
15. Insert key A-2 in L-O interlock on breaker C and turn to unlock.
Key A-2 is now held and Key A-3 is now free.
16. Breaker C may now be operated for servicing.
17. Insert key A-3 in L-O interlock on breaker D and turn to unlock.
Key A-3 is now held and key A-4 is now free.
18. Breaker D may now be operated for servicing.
19. Insert key A-4 in L-O interlock on breaker E and turn to unlock.
Key A-4 is now held and supervisor Key A-5 is now free.
20. Breaker E may now be operated for servicing.

Scheme 9
To prevent operation of disconnects A and B with breaker C closed. To Disconnects A and B, breaker C, and door are normally closed. Keys
prevent access to breaker compartment with disconnects closed. A-1 are held in L-O interlock on breaker C and L-O interlock on
disconnect B. Key A-2 is held in the L-O interlock on disconnect A. Key
A-3 is held in L-O interlock on disconnect B.
E 1. Open breaker.
A 1 2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
is now free.
L-O 3. Insert key A-1 in L-C interlock on disconnect A and turn to
A B 4. Open disconnect A.
5. Turn key A-2 in L-O interlock on disconnect A to lock open.
C Key A-2 is now free.
6. Insert key A-2 in L-C interlock on disconnect B and turn to
7. Open disconnect B.
8. Turn keys A-1 and A-3 in L-O interlock on disconnect B to
E E E E
lock open. Keys A-1 and A-3 are now free.
A-1 A2 A-2 A 1 9. Insert key A-1 in breaker L-O interlock and turn to unlock for
E
E
operation during servicing.
A-3 10. Insert key A-3 in L-C interlock (type D) on compartment door
L-C L-O L-C A3
and turn to unlock. Key A-3 is now held.
L-C 11. Open compartment door to service breaker.
L-O
Scheme 10
To prevent operation of disconnects A and B and by-pass disconnect To transfer load from breaker and disconnects to by-pass switch:
C under load. Provides for closing of by-pass disconnect C before
breaker circuit is opened, or permits breaker circuit to be opened with 1. Obtain key A-3 which is free and insures that both
by-pass disconnect C remaining open. disconnects A and B are locked closed.
2. Insert key A-3 in L-C interlock on breaker D and turn to lock
Disconnects A and B and breaker D normally closed. By-pass closed. Key A-3 is held and key A-4 is now free.
disconnect C normally open. Keys A-1, A-2, and A-4 normally held in 3. Insert key A-4 in L-O-C interlock on by-pass disconnect C and
locks as indicated. Key A-3 normally free. turn to unlock. Key A-4 is now held.
4. Close by-pass disconnect C.
5. Turn key A-4 in L-O-C interlock on by-pass disconnect C to
lock closed. Key A-4 is now free.
E
A-4 6. Insert key A-4 in L-C interlock on breaker D and turn to unlock.
Key A-4 is held and key A-3 is now free.
L-O-C
7. Open breaker D.
8. Turn key A-1 in L-O interlock on breaker D to lock open. Key A-
C 1 is now free.
9. Insert keys A-1 and A-3 in L-C interlock on disconnect A and
turn to unlock. Keys A-1 and A-3 are now held.
11. Turn key A-2 in L-O interlock on disconnect A to lock open.
A B Key A-2 is now free.
D 12. Insert key A-2 in L-C interlock on disconnect B and turn to
14. Turn key A-1 in L-O interlock on disconnect B to lock open.
15. Insert key A-1 in L-O interlock on breaker D and turn to unlock
E E E W E E
A 1 A-2
to permit operation during servicing.
A 2 A 3 A1 A-3
E E
A 4
To open disconnects A and B and breaker D, leaving by-pass
L-O A-1 L-O L-O L-C
disconnect C open:
L-C L-C
1. Proceed from normal position with operations as in 7 to 15
above.
Scheme 10A Scheme 11
To prevent operation of disconnect A and B and by-pass disconnect C To prevent paralleling of lines A and B. Single load, fed from either
under load. Permits by-pass disconnect C to operate only when source.
regulator is in neutral position. Permits isolating regulator for servicing.
A-1 A 2
L-O L-C
C
A B
Disconnect C shown closed and disconnect D shown open. Key A-1 is
REGULATOR held in disconnect C interlock.
1. Open switch C.
2. Turn key A-1 in L-O interlock on switch C to lock open. Key A-1
is now free.
3. Insert key A-1 in L-O interlock on switch D and turn to unlock.
A-3 A1 A 1 A-2 A3 Key A-1 is now held.
4. Close switch D.
L-C L-O L-N L-C L-O
Reverse sequence to restore service through switch C.
Disconnects A and B are normally closed. Regulator is normally in

operation. By-pass disconnect C is normally open.
One key A-1 is held in regulator L-N (locked neutral) interlock and the
second key A-1 is held in L-O interlock on disconnect A. Key A-2 is held
in L-C interlock on disconnect C. Key A-3 is held in L-O interlock on
disconnect B.
1. Operate regulator to neutral position.

2. Turn key A-1 in L-N interlock on regulator to lock in neutral
position. Key A-1 is now free.
3. Insert key A-1 in L-O interlock on by-pass disconnect C and
4. Close by-pass disconnect C.
5. Turn key A-2 in L-C interlock on by-pass disconnect C to lock
closed. Key A-2 is now free.
6. Insert key A-2 in L-C interlock on disconnect B and turn to
8. Turn key A-3 in L-O interlock on disconnect B to lock open. Key
A-3 is now free.
9. Insert key A-3 in L-C interlock on disconnect A and turn to
11. Turn key A-1 in L-O interlock on disconnect A to lock open. Key
A-1 is now free.
12. Insert key A-1 in regulator L-N interlock and turn to unlock. This
permits regulator to be operated during inspection and
servicing.

Scheme 12
To prevent paralleling of lines A and B. Single load, fed from either 3. Insert key A-1 in L-O-C interlock on disconnect A and turn to
source. To prevent operation of disconnect switches A and B when unlock. Key A-1 is now held.
breaker C is closed. 4. Open disconnect A.
A A B B 6. Return key A-1 to breaker interlock and unlock for operation
To transfer load from line A to line B:
C 1. Open breaker C.
2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
A2 A-1 A-1 A-2 is now free.
A 1 3. Insert key A-1 in L-O-C interlock on disconnect A and turn to
L-O L-O-C L-O-C L-O unlock. Key A-1 is now held.
L-O 4. Open disconnect A.
5. Turn key A-1 in L-O-C interlock and key A-2 in L-O interlock on
disconnect A to lock open. Keys A-1 and A-2 are now free.
6. Insert key A-1 in L-O-C interlock on disconnect B and turn to
7. Insert key A-2 in L-O interlock on disconnect B and turn to
Breaker C and disconnect A are shown in closed position. Disconnect unlock. Key A-2 is now held.
B is shown in open position. Key A-1 is held in breaker C interlock. Key A- 8. Close disconnect B.
2 is held in L-O interlock on disconnect A. 9. Turn key A-1 in L-O-C interlock on disconnect B to lock
To service breaker: 10. Insert key A-1 in breaker interlock and turn to unlock. Key A-1
is now held.
1. Open breaker C. 11. Close breaker.
is now free. Reverse sequence to restore service through line A.
Scheme 13
To prevent paralleling of lines A and B. Two loads, fed from either source. Breaker A is closed to supply load M. Breaker B is closed to supply load
N. Tie-breaker C is open. Keys A-1 are held in interlocks on both
breakers A and B. Tie-breaker C cannot be closed unless either A or B
is locked open.
To transfer load N to breaker A:
1. Open breaker B
2. Turn key A-1 in L-O interlock on breaker B to lock open. Key
A B A-1 is now free.
3. Insert key A-1 in L-O interlock on tie-breaker C and turn to
C 4. Close tie-breaker C.
M N Load M can be supplied through breaker B in a similar manner.

Scheme 14 Scheme 15 - (Continued)
To prevent paralleling of lines A and B. Two loads, fed from either source
(one tie-breaker). To prevent operation of disconnect switch D when
breaker A is closed. To prevent operation of disconnect switch E when
D E
breaker B is closed.
A-2 A 3 A 5 A-4
L-O-C L-O L-O L-O-C
D E
A-2 A-3
A-3 A-5
L-O-C L-O-C A-2 A-4
L-C L-C
A B
A2 A 3
A B
C A2 A 4
C
L-O L-O A 1 A 1
M N L-O L-O
Disconnect switches D and E and breakers A and B are closed. Breaker M N

A closed to supply load M. Breaker B closed to supply load N. Tie-
breaker C is open. Keys A-1 and A-2 are held in interlock on breaker A. Disconnect switch D and breaker A are closed to supply load M. Disconnect
Keys A-1 and A-3 are held in interlock on breaker B. Tie-breaker C switch E and breaker B are closed to supply load N. Tie-breaker C is open.
cannot be closed until either breaker A or B is locked open. Keys A-1 and A-2 are held in interlock on breaker A. Key A-3 is held in L-O
interlock on disconnect D. Keys A-1 and A-4 are held in interlock on breaker
To transfer load N to breaker A: B. Key A-5 is held in L-O interlock on disconnect E. Tie-breaker C cannot be
closed until either breaker A or B is locked open.
1. Open breaker B.
To transfer load N to breaker A, proceed as follows:
2. Turn key A-1 in L-O interlock on breaker B to lock open. Keys A-
1. Open breaker B.
1 and A-3 are now free.
2. Turn key A-1 in L-O interlock on breaker B to lock open. Keys A-1
3. Insert key A-1 in L-O interlock on tie-breaker C and turn to and A-4 are now free.
unlock. Key A-1 is now held. 3. Insert key A-1 in L-O interlock on tie-breaker C and turn to unlock.
4. Close tie-breaker C. Key A-1 is now held.
4. Close tie-breaker C.
Reverse sequence to restore service through breaker B. Load M can be
Reverse sequence to restore service through breaker B. Load M can be supplied through breaker B in a similar manner.
supplied through breaker B in a similar manner.
To service breaker B, proceed as follows:
1. Open breaker B.
To service breaker B: 2. Turn key A-1 in L-O interlock on breaker B to lock open. Keys A-1
and A-4 are now free.
1. Open breaker B. 3. Insert key A-4 in L-O-C interlock on disconnect E and turn to
2. Turn key A-1 in L-O interlock on breaker B to lock open. Keys A- unlock. Key A-4 is now held.
4. Open disconnect E.
1 and A-3 are now free.
5. Turn key A-4 in L-O-C interlock on disconnect E to lock open. Key
3. Insert key A-3 in L-O-C interlock on disconnect E and turn to
A-4 is now free.
unlock. Key A-3 is now held. 6. Return key A-4 to L-O interlock on breaker B and unlock for
4. Open disconnect E. operation of breaker during servicing.
5. Turn key A-3 in L-O-C interlock on disconnect E to lock open. Reverse sequence to restore service. Breaker A can be serviced in a similar
Key A-3 is now free. manner.
6. Return key A-3 to L-O interlock on breaker B and unlock for
operation of breaker during servicing. To enter fuse compartment on line B, proceed as follows:
1. Open breaker B.
Reverse sequence to restore service. Breaker A can be serviced in a 2. Turn key A-1 in L-O interlock on breaker B to lock open. Keys A-1
similar manner. and A-4 are now free.
3. Insert key A-4 in L-O-C interlock on disconnect E and turn to
5. Turn key A-4 in L-O-C interlock on disconnect E to lock open. Key
Scheme 15 A-4 is now free.
6. Turn key A-5 in L-O interlock on disconnect E to lock open. Key A-5
To prevent paralleling of lines A and B. Two loads, fed from either source (one is now free.
tie-breaker). To prevent operation of disconnect D when breaker A is closed. 7. Insert keys A-4 and A-5 in L-C interlock on fuse compartment door
To prevent operation of disconnect switch E when breaker B is closed. To and turn to unlock. Keys A-4 and A-5 are now held.
prevent opening fuse compartment door when the associated disconnects 8. Open fuse compartment door.
D or E and breakers A and B are closed. Reverse sequence to restore service. Fuse compartment on line A can be
entered in a similar manner.
Scheme 16
To prevent paralleling of lines A, B, and C. Three loads, fed from any Tie-breaker D interlock has a master or apartment lock and can be
source (two tie-breakers). unlocked for operation with either keys A-1 or B-1. Tie-breaker E has a
master or apartment lock and can be unlocked for operation with
A B C either keys B-1 or C-1.
To transfer load M from Breaker A to breaker B:

A1 A B1 B C1 C 1. Open breaker A
2. Turn key A-1 in L-O interlock on breaker A to lock open. Key A-
1 is now free.
3. Insert Key A-1 in L-O interlock on tie-breaker D and turn to
D E unlock. Key A-1 is now held.
4. Close tie-breaker D.
Reverse sequence to restore service through breaker A.
A-1 B-1
To transfer load M and N from breakers A and B to breaker C:
B-1 C-1
1. Close tie-breaker D as above.
L-O L-O
2. Turn key B-1 in L-O interlock on breaker B to lock open. Key B-
1 is now free.
M N P
3. Insert key B-1 in L-O interlock on tie-breaker E and turn to
unlock. Key B-1 is now held.
4. Close tie-breaker E.
Breaker A is closed to supply load M. Breaker B is closed to supply load Reverse sequence to restore service (M and N through breakers A
N. Breaker C is closed to supply load P. Keys A-1, B-1, and C-1 are held and B).
in L-O interlocks of breakers A, B, and C. Tie-breakers D and E are
locked open. Any of the loads M, N, or P can be transferred from its own supply to
any adjacent supply.
A-1
Note: This symbol represents an interlock with an apartment lock. An apartment lock is a single cylinder that will accept two
B-1
different keys - but only one key at a time.
Scheme 17
To prevent paralleling lines A, B, C, and D. Four loads, fed from any To transfer load M from breaker A to breaker B:
source (three tie-breakers).
1. Open breaker A.
2. Turn key A-1 in L-O interlock on breaker A to lock open. Key A-1 is
now free.
A B C D 3. Insert key A-1 in L-O interlock on tie-breaker E and turn to unlock.
Key A-1 is now held.
E E
E E
A1 A B1 B C1 C D1 D Reverse sequence to restore service through breaker A.
To transfer load M and N from breaker A and B to breaker C:
E F G 1. Close tie-breaker E as above.

2. Open breaker B.
3. Turn key B-1 in L-O interlock on breaker B to lock open. Key B-1 is
E E E
now free.
A-1 B-1 C-1 4. Insert key B-1 in L-O interlock on tie-breaker F and turn to unlock.
B-1 C-1 D-1 Key B-1 is now held.
L-O L-O L-O 5. Close tie-breaker F.
Reverse sequence to restore service (M and N) through breakers A and B.
M N P R
To transfer load R from breaker D to breaker C:
Breaker A is closed to supply load M. Breaker B is closed to supply load 1. Open breaker D.
N. Breaker C is closed to supply load P. Breaker D is closed to supply 2. Turn key D-1 in L-O interlock on breaker D to lock open. Key D-1 is
load R. Keys A-1, B-1, C-1, and D-1 are held in L-O interlocks of now free.
breakers A, B, C, and D. Breakers E, F and G are locked open. Breaker E 3. Insert key D-1 in L-O interlock on tie-breaker G and turn to unlock.
interlock has a master or apartment lock and can be unlocked for Key D-1 is now held.
operation with either key A-1 or B-1. Breaker F interlock has a master or 4. Close tie-breaker G.
apartment lock and can be unlocked for operation with either key B-1 Reverse sequence to restore service through breaker D.
or C-1. Breaker G interlock has a master or apartment lock and can be
unlocked for operation with either key C-1 or D-1. Any of the loads M, N, P, or R can be transferred from its own supply to any
adjacent supply.
A-1
B-1
Scheme 17A
To prevent paralleling lines A, B, C, and D. To prevent opening All loads can be transferred as described in scheme 17.
rear access doors when breakers are energized.
To open rear access doors K-1, K-2, and K-3:
1. Open breaker A.
2. Turn key A-1 in L-O interlock on breaker A to lock
ACCESS ACCESS ACCESS ACCESS ACCESS ACCESS ACCESS ACCESS ACCESS 3. Open breaker B.
DOOR DOOR DOOR DOOR DOOR DOOR DOOR DOOR DOOR
#1 #2 #3 #4 #5 #6 #7 #8 #9 4. Turn key B-1 in L-O interlock on breaker B to lock open.
E E E E E E E E E
Key B-1 is now free.
K-1 K-2 K-3 K-4 K-5 K-6 K-7 K-8 K-9 5. Insert key A-1 and B-1 in transfer interlock.
L-C L-C L-C L-C L-C L-C L-C L-C L-C 6. Turn key A-1 in transfer interlock. Keys K-1, K-2, and K-
3 are now free. Keys A-1 and B-1 are now held.
7. Insert keys K-1, K-2, and K-3 in their respective rear
access door interlocks and turn to unlock. Keys K-1,
K-2, and K-3 are now held.
K3 W W K6 W K9
8. Open the rear access doors.
K2 W K5 W W K8
K1 W K4 W K7 W
E B-1 E C-1 E D-1 To open rear access doors K-4, K-5 and K-6
A-1 E B-1 E C-1 E
1. Open breaker B.
T T T 2. Turn key B-1 in L-O interlock on breaker B to lock open.
Key B-1 is now free.
3. Open breaker C.
A B C D 4. Turn key C-1 in L-O interlock on breaker C to lock
E E E E
open. Key C-1 is now free.
A1 A B1 B C1 C D1 D 5. Insert key B-1 and C-1 in transfer interlock.
6. Turn key B-1 in transfer interlock. Keys K-4, K-5, and K-
6 are now free. Keys B-1 and C-1 are now held.
7. Insert keys K-4, K-5, and K-6 in their respective rear
E F G
access door interlocks and turn to unlock. Keys K-4,
K-5, and K-6 are now held.
E E E 8. Open the rear access doors.
A-1 B-1 C-1
B-1 C-1 D-1
L-O L-O L-O Reverse sequence to restore service.
M N P R To open rear access doors K-7, K-8 and K-9

1. Open breaker C.
2. Turn key C-1 in L-O interlock on breaker C to lock
open. Key C-1 is now free.
3. Open breaker D.
4. Turn key D-1 in L-O interlock on breaker D to lock
open. Key D-1 is now free.
Breakers A, B, C, and D are closed to supply their respective 5. Insert key C-1 and D-1 in transfer interlock.
loads. Keys A-1, B-1, C-1, and D-1 are held in L-O interlocks of 6. Turn key C-1 in transfer interlock. Keys K-7, K-8, and K-
breakers A, B, C, and D. Tie-Breakers E, F, and G are locked 9 are now free. Keys C-1 and D-1 are now held.
open. Breaker E interlock has an apartment lock and can be 7. Insert keys K-7, K-8, and K-9 in their respective rear
unlocked for operation with either key A-1 or B-1. Breaker F access door interlocks and turn to unlock. Keys K-7,
interlock has an apartment lock and can be unlocked for K-8, and K-9 are now held.
operation with either key B-1 or C-1. Breaker G interlock has an 8. Open the rear access doors.
apartment lock and can be unlocked for operation with either
key C-1 or D-1. All rear access doors are locked closed. All Reverse sequence to restore service.
keys for rear access doors (K-1 through K-9) are held in transfer
interlocks.
A-1
B-1
Scheme 18 Scheme 19
To prevent paralleling of lines A, B, and C. Three loads, fed from any To prevent paralleling lines A, B, C, and D. Four loads fed from any source
source (three tie-breakers). (four tie-breakers).
A B C D
A B C
A1 A B1 B C1 C D1 D
A1 A B1 B C1 C
B-1
C-1
D E L-O
N E F G
A-1 B-1
A-1 C-1
B-1 C-1
A-1
B-1 D-1
L-O L-O D-1
L-O L-O
L-O
A-1
C-1
H
L-O
M N P R
F E
Breaker A is closed to supply load M. A B
M P Breaker B is closed to supply load N.
H F
Breaker C is closed to supply load P.
Breaker A is closed to supply load M. Breaker B is closed to supply load Breaker D is closed to supply load R. D C
G
N. Breaker C is closed to supply load P. Keys A-1, B-1, and C-1 are held
in L-O interlocks on breakers A, B and C. Tie-breakers D, E, and F are Keys A-1, B-1, C-1, and D-1 are held in L-O interlocks of breakers A, B, C, and
locked open. Master or apartment lock interlocks are mounted on tie- D. Tie breakers E, F, G, and H are locked open. Breaker E interlock has a
master or apartment lock and can be unlocked with either key A-1 or B-1.
breakers D, E, and F, and can be unlocked for operation with either Breaker F interlock has a master or apartment lock and can be unlocked
keys A-1 or B-1, B-1 or C-1, and A-1 or C-1, respectively. with either key B-1 or C-1. Breaker G interlock has a master or apartment lock
and can be unlocked with either key C-1 or D-1. Breaker H interlock has a
A
master or apartment lock and can be unlocked with either key A-1 or D-1.
D
To transfer load M from breaker A to breaker B:
F
1. Open breaker A.
C
E
B
now free.
3. Insert key A-1 in L-O interlock on tie-breaker E and turn to unlock.
To transfer load M from breaker A to breaker B: Key A-1 is now held.
1. Open breaker A. 4. Close tie-breaker E.
2. Turn key A-1 in L-O interlock on breaker A to lock open. Key A- Reverse sequence to restore service through breaker A.
1 is now free.
3. Insert key A-1 in L-O interlock on tie-breaker D and turn to To transfer load M and N from breaker A and B to breaker C:
unlock. Key A-1 is now held. 1. Close tie-breaker E as above.
4. Close tie-breaker D. 2. Open breaker B.
Reverse sequence to restore service through breaker A. 3. Turn key B-1 in L-O interlock on breaker B to lock open. Key B-1 is
now free.
4. Insert key B-1 in L-O interlock on tie-breaker F and turn to unlock.
To transfer load M and N from breakers A and B to breaker C: Key B-1 is now held.
1. Close tie-breaker D as above. 5. Close tie-breaker F.
2. Open breaker B. Reverse sequence to restore service (M and N) through breakers A and B.
1 is now free. To transfer load R from breaker D to breaker C:
4. Insert key B-1 in L-O interlock on tie-breaker E and turn to 1. Open breaker D.
unlock. Key B-1 is now held. 2. Turn key D-1 in L-O interlock on breaker D to lock open. Key D-1 is
now free.
3. Insert key D-1 in L-O interlock on tie-breaker G and turn to unlock.
Reverse sequence to restore service (loads M and N) through breakers Key D-1 is now held.
A and B. 4. Close tie-breaker G.
Reverse sequence to restore service through breaker D.
To transfer load P from breaker C to breaker A:
1. Open breaker C. To transfer load M from breaker A to breaker D:
2. Turn key C-1 in L-O interlock on breaker C to lock open. Key 1. Open breaker A.
C-1 is now free. 2. Turn key A-1 in L-O interlock on breaker A to lock open. Key A-1 is
3. Insert key C-1 in L-O interlock on tie breaker F and turn to now free.
unlock. Key C-1 is now held. 3. Insert key A-1 in L-O interlock on tie-breaker H and turn to unlock.
4. Close tie-breaker F. 4. Close tie-breaker H.
Reverse sequence to restore service through breaker C. Reverse sequence to restore service through breaker A.
Any of the loads M, N, P, or R can be transferred from its own supply to any
adjacent supply.
A-1 Note: This symbol represents an interlock with an apartment A-1 Note: This symbol represents an interlock with an apartment
B-1 lock. An apartment lock is a single cylinder that will accept B-1 lock. An apartment lock is a single cylinder that will accept
two different keys - but only one key at a time. two different keys - but only one key at a time.
Scheme 20
To prevent paralleling three power sources through a common tie bus not Breakers A, B, and C are normally closed. Breakers D, E, and F are normally
normally in service. To permit feeding any load bus from a second power open. Under normal conditions keys A-1 and A-5 are held in breaker A
source through the tie bus. To permit one power source to supply all three interlock, keys A-2 and A-5 are held in breaker B interlock, and keys A-3 and
load busses through the tie bus. A-5 are held in breaker C interlock.
To transfer load from line No. 1 to line No. 2 or line No. 3 through the tie
Line 1 Line 2 Line 3 bus, proceed as follows:
1. Open breaker A.
2. Turn key A-1 in L-O interlock on breaker A to lock breaker open.
Keys A-1 and A-5 are now free.
3. Insert key A-1 in L-O interlock on breaker D and turn to unlock.
A A5 B A5 C A5
4. Close breaker D.
5. Insert key A-5 in L-O interlock on either breaker E or F and turn to
A1 A2 A3
L-O L-O L-O
6. Close breaker E or F (whichever is selected).
Reverse sequence to restore load to line No. 1.
Load Bus Load Bus Load Bus
To transfer load from lines No. 1 and No. 2 to line No. 3 through tie bus,
proceed as follows:
D A-1 E A-2 F A-3 1. Close breaker D as per steps 1 to 4 above.

A-5 A-5 A-5 2. Open breaker B.
3. Turn key A-2 in L-O interlock on breaker B to lock breaker open.
L-O L-O L-O
Keys A-2 and A-5 are now free.
4. Insert key A-2 in L-O interlock on breaker E and turn to unlock.
5. Close breaker E.
Tie Bus 6. Insert one of the A-5 keys from either breaker A or B in L-O
interlock on breaker F and turn to unlock. Key A-5 is now held.
7. Close breaker F.
Reverse sequence to restore load to lines No. 1 and No. 2.
A-1
B-1
Scheme 21
To prevent paralleling three power sources through a common tie bus not Breakers A, B, and C are normally closed. Breakers D, E, and F are normally
normally in service. To permit feeding any load bus from a second power open. Under normal conditions key A-1 is held in breaker A interlock, key A-2 is
source through the tie bus only when authorized by supervisor. To permit held in breaker B interlock, and key A-3 is held in breaker C interlock. Key A-5 is
one power source to supply all three load busses through the tie bus only retained by supervisor.
when authorized by supervisor.
To transfer load from line No. 1 to line No. 2 or line No. 3 through tie bus,
Line 1 Line 2 Line 3 proceed as follows:
1. Open breaker A.
2. Turn key A-1 in L-O interlock on breaker A to lock breaker open. Key
A-1 is now free.
3. Insert key A-1 in L-O interlock on breaker D and turn to unlock. Key
A-1 is now held.
A A1
B A2
C A3 4. Close breaker D.
5. Insert supervisor's key A-5 (only one A-5 is available) in L-O interlock
on either breaker E or F and turn to unlock. Key A-5 is now held.
6. Close breaker E or F (whichever is selected).
Load Bus Load Bus Load Bus Reverse sequence to restore load to line No. 1.
To transfer load from lines No. 1 and No. 2 to line No. 3 through tie bus,
A-1 A-2 A-3
proceed as follows:
D E F 1. Close breaker D as per steps 1 to 4 above.
A-5 A-5 A-5
2. Open breaker B.
L-O L-O L-O 3. Turn key A-2 in L-O interlock on breaker B to lock breaker open. Key
A-2 is now free.
4. Insert key A-2 in L-O interlock on breaker E and turn to unlock. Key
A-2 is now held.
5. Close breaker E.
Tie Bus 6. Insert supervisor's key A-5 in L-O interlock on breaker F and turn to
A 5
SUPERVISORY
KEY 7. Close breaker F.
Reverse sequence to restore load to lines No. 1 and No. 2.
A-1
B-1
Scheme 22 Scheme 23 (Continued)
To prevent paralleling incoming primary sources, lines 1 and 2, through
primary tie bus disconnect. To prevent operation (open or closed) of the Line 1 Line 2
disconnects under load. Permits one power source to supply both loads
through tie bus.
Line 1 Line 2
D E
A2 A4 A4 A2
C D L-O A-1 A1 A-4 A-3 L-O
A2 A4 A4 A2
L-C A3 A-2 L-C
L-O A-1 A1 A-4 A-3 L-O

L-C L-O
L-C A3 A-2 L-C
L-C L-O
T
T
A5 A C B A5
A1 A3
A B A3 A-5
L-O L-O
L-O L-O L-O
Load 1 Load 2
Load 1 Load 2
Under normal conditions breakers A and B are closed, disconnects C and

Under normal conditions breakers A and B are closed, breaker C is locked
D are locked closed, and tie bus disconnect T is locked open. Keys A-1 are
open, disconnects D and E are locked closed, and tie disconnect T is
held in L-O interlock on breaker A and L-C interlock on tie bus disconnect T.
locked open. Keys A-1 are held in L-O interlock on breaker A and L-C
Keys A-2 are held in L-O interlock on disconnects C and D. Keys A-3 are
interlock on primary tie bus disconnect T. Keys A-2 are held in L-O interlocks
held in L-O interlock on breaker B and L-C interlock on tie bus disconnect T.
on disconnects D and E. Keys A-3 are held in L-O interlock on breaker B and
Keys A-4 (free keys) are shown removably held in the L-C interlocks on
L-C interlock on primary tie bus disconnect T. Keys A-4 (free keys) are shown
disconnects C and D.
removably held in the L-C interlocks on disconnects D and E. Keys A-5 are
held in L-O interlocks on breakers A and B.
To transfer load No. 1 from line 1 to line 2 through bus tie disconnect T,
proceed as follows:
To transfer load No. 1 from line 1 to line 2 through primary bus tie disconnect
1. Open breaker A.
T, proceed as follows:
1. Open breaker A.
now free.
2. Turn key A-1 in L-O interlock on breaker A to lock open. Keys A-1
3. Insert key A-1 in L-C interlock on disconnect C and turn to unlock.
Keys A-1 and A-4 are now held.
3. Insert key A-1 and free key A-4 in L-C interlock on disconnect D
4. Open disconnect C.
and turn to unlock. Keys A-1 and A-4 are now held.
5. Turn key A-2 in L-O interlock on disconnect C to lock open. Key A-
4. Open disconnect D.
2 is now free.
5. Turn key A-2 in L-O interlock on disconnect D to lock open. Key A-
6. Insert keys A-2 and free key A-4 (from L-C interlock on disconnect
2 is now free.
D) in L-O interlock on bus tie disconnect T and turn to unlock.
6. Insert key A-2 and free key A-4 (from L-C interlock on disconnect
Keys A-2 and A-4 are now held.
E) in L-O interlock on primary bus tie disconnect T and turn to
7. Close tie bus disconnect T.
unlock. Keys A-2 and A-4 are now held.
8. Turn key A-3 in L-C interlock on disconnect T to lock closed. Keys
7. Close bus tie disconnect T.
A-1 and A-3 are now free.
8. Turn key A-3 in L-C interlock on bus tie disconnect T to lock closed.
9. Insert key A-1 in L-O interlock on breaker A and turn to unlock. Key
Keys A-1 and A-3 are now removable.
A-1 is now held.
9. Insert key A-1 in L-O interlock on breaker A and turn to unlock. Key
10. Close breaker A.
A-1 is now held.
Reverse sequence to restore load No. 1 to line 1. To transfer load No. 2
10. Close breaker A.
from line 2 to line 1 through bus tie disconnect T, proceed in a similar
Reverse procedure to restore service to line 1. Load No. 2 can be supplied
manner.
from No. 1 through the primary bus tie in a similar manner.
To transfer load No. 1 from line 1 to line 2 through the secondary tie breaker
C, proceed as follows:
1. Open breaker A.
Scheme 23 2. Turn key A-1 in L-O interlock on breaker A to lock open. Keys A-1
and A-5 are now removable.
To prevent paralleling incoming primary sources, lines 1 and 2, through the 3. Insert key A-5 in L-O interlock on tie breaker C and turn to unlock.
primary tie bus disconnect or the secondary tie bus breaker. To prevent Key A-5 is now held.
operation (open or closed) of the disconnects under load. Permits one 4. Close tie breaker C.
power source to supply both loads through either the primary or secondary Reverse procedure to restore service on line 1. Load No. 2 can be supplied
tie bus. from line No. 1 through the secondary tie breaker C in a similar manner.
Scheme 24
To prevent paralleling incoming primary sources, lines 1 and 2. To To transfer load No. 1 from line 1 to line 2 through bus tie disconnect T,
prevent operation (open or closed) of the disconnects under load. proceed as follows:
(Permits transformer primary disconnects K & L to open and close the
transformer magnetizing current.*) Permits isolating breakers for 1. Open breaker A.
servicing. Permits one power source to supply both loads through tie 2. Turn key A-2 in L-O interlock on breaker A to lock open. Key
bus. A-2 is now free.
3. Open breaker C.
4. Turn key A-4 in L-O interlock breaker C to lock open. Keys A-1
Line 1 Line 2 5. Insert key A-2 from L-O interlock on breaker A and key A-1
from L-O interlock on breaker C in L-C interlock on
disconnect F and turn to unlock. Keys A-1 and A-2 are now
held.
E G 6. Open disconnect F.
A-3 A2 B2 B-3
7. Turn key A-3 in L-O interlock on disconnect F to lock open.
Keys A-3 and T-1 are now free.
L-C L-O L-O L-C 8. Insert key T-1 in L-O interlock on bus tie disconnect T and turn
to unlock. Key T-1 is now held.
9. Close bus tie disconnect T.
A B 10. Turn key B-1 in L-C interlock on bus tie disconnect T to lock
A2 B2 closed. Keys A-1 and B-1 are now free.
11. Insert key A-1 in L-O interlock on breaker C and turn to
L-O L-O unlock. Keys A-1 and A-4 are now held.
12. Close breaker C.
F H Reverse sequence to restore load No. 1 to line 1. To transfer load No.
T1 A-1 A1 B-1 T1
2 from line 2 to line 1, proceed in a similar manner.
A3 A-2 B1 T-1 B-2 B3
To isolate breaker A for servicing, proceed as follows:
L-O L-C L-C L-O L-C L-O
1. Proceed from normal position with operations as in 1
through 7 above.
2. Insert key A-3 in L-C interlock on disconnect E and turn to
T unlock. Key A-3 is now held.
K L 4. Turn key A-2 in L-O interlock on disconnect E to lock open.
A-4 B-4
5. Return key A-2 to breaker A and unlock for operation during
L-O-C L-O-C servicing.
Reverse sequence to restore service. To isolate breaker B for servicing,

proceed in a similar manner.
A1 C D B1 To isolate breaker C for servicing, proceed as follows:
A4 B4
1. Open breaker C.
L-O L-O
2. Turn key A-4 in L-O interlock on breaker C to lock breaker
open. Keys A-1 and A-4 are now free.
Load 1 Load 2
3. Insert key A-4 in L-O-C interlock on disconnect K and turn to
4. Open disconnect K.
5. Turn key A-4 in L-O-C interlock on disconnect K to lock open.
Under normal conditions breakers A, B, C, and D are closed, Key A-4 is now free.
disconnects E, F, G, H, K, and L are locked closed, and bus tie 6. Return key A-4 to breaker C and unlock for operation during
disconnect T is locked open. Keys A-1 are held in L-O interlock on servicing.
breaker C and L-C interlock on bus tie disconnect T. Keys A-2 are held
in L-O interlocks on breaker A and disconnect E. Key A-3 is held in L-O Reverse sequence to restore service. To isolate breaker D for servicing,
interlock on disconnect F. Key A-4 is held in L-O interlock on breaker C. proceed in a similar manner.
Keys B-1 are held in L-O interlock on breaker D and L-C interlock on bus
tie disconnect T. Keys B-2 are held in L-O interlocks on breaker B and * To prevent primary disconnects K and L from opening magnetizing
disconnect G. Key B-3 is held in L-O interlock on disconnect H. Key B-4 current only, additional interlocks should be provided for disconnect K
is held in L-O interlock on breaker D. Keys T-1 are held in L-O interlock and L.
on disconnects F and H.
Scheme 25 Scheme 27
To prevent opening fuse compartment door when the interrupter switch To prevent operation (open or closed) of interrupter switch A when
A is closed. To prevent closing interrupter switch until fuse compartment breaker is closed. To prevent opening fuse compartment door when
door is locked closed. the interrupter switch A is closed. To prevent closing interrupter switch
until fuse compartment door is locked closed. Permits the breaker to be
serviced and operated while the interrupter is locked open.
A
A
E E
A 1 A-1
L-O L-C E E E E
A 1 A-1 A 2 A-2
Fuse compartment door and interrupter are shown in closed position. L-O L-O-C L-O L-C
Key A-1 is held in interrupter interlock.
1. Open interrupter.
2. Turn key A-1 in L-O interlock on interrupter switch to lock open.
3. Insert key A-1 in L-C interlock on fuse compartment door and A
4. Open fuse compartment door.

E E E E
A 1 A-2 A 2 A-1
Scheme 26
L-O L-C L-O L-O-C
To prevent operation (open or closed) of interrupter switch A when
breaker is closed. Permits the breaker to be serviced and operated
while the interrupter switch is locked open.
Breaker, fuse compartment door and interrupter are shown in closed

A position. Key A-1 is held in breaker interlock and key A-2 is held in
interrupter interlock.
To service breaker, proceed as follows:
1. Open breaker.
E E
A 1 A-1 is now free.
3. Insert key A-1 in L-O-C interlock on interrupter and turn to
L-O L-O-C unlock. Key A-1 is now held.
5. Turn key A-1 in L-O-C interlock on interrupter to lock open. Key
Interrupter and breaker are shown in closed position. Key A-1 is held in
A-1 is now free.
breaker interlock.
1. Open breaker.
is now free.
3. Insert key A-1 in L-O-C interlock on interrupter and turn to
To open fuse compartment door, proceed as follows:
1. Proceed from normal position with operations as in 1 through
5. Turn key A-1 in L-O-C interlock on interrupter to lock open. Key
4 above.
A-1 is now free.
2. Turn key A-2 in L-O interlock on interrupter switch to lock open.
3. Insert key A-2 in L-C interlock on fuse compartment door and

Scheme 28
To prevent dropping load when shifting from one source to the other. Interrupter switch A is shown closed and interrupter switch B is shown
To prevent opening both interrupter switches A and B at the same open. Key A-1 is held in interrupter B interlock.
time. Permits both interrupter switches to be closed at the same time.
1. Close interrupter B.
2. Turn key A-1 in L-C interlock on interrupter B to lock closed.
A B 3. Insert key A-1 in L-C interlock on interrupter A and turn to
E E
A-1
A 1
4. Open interrupter A.
L-C L-C
Reverse sequence to restore service through interrupter A.
Scheme 29
To prevent paralleling lines A and B requires dropping load when Interrupter switch A is shown closed and interrupter switch B is shown
shifting from one source to the other. To prevent closing both interrupter open. Key A-1 is held in interrupter switch A interlock.
switches A and B at the same time. Permits both interrupter switches to
be opened at the same time. 1. Open interrupter A.
2. Turn key A-1 in L-O interlock on interrupter A to lock open. Key
A-1 is now free.
3. Insert key A-1 in L-O interlock on interrupter B and turn to
A unlock. Key A-1 is now held.
B 4. Close interrupter B.
E E
A 1 A-1
Reverse sequence to restore service through interrupter A.
L-O L-O
Scheme 30
To prevent paralleling lines A and B requires dropping load when To service breaker, proceed as follows:
shifting from one source to the other. To prevent closing both interrupter
switches A and B at the same time. Permits both interrupter switches to 1. Open breaker.
be opened at the same time. To prevent operation (open or closed) of 2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
either interrupter switch when breaker is closed. Permits breaker to be is now free.
serviced and operated while both interrupter switches are locked 3. Insert key A-1 in L-O-C interlock on interrupter A and turn to
open. unlock. Key A-1 is now held.
4. Open interrupter A.
5. Turn key A-1 in L-O-C interlock on interrupter A to lock open.
A B 6. Return key A-1 to breaker interlock and unlock for operation
E E E E of breaker during servicing.
A 2 A-1 A-2 A-1 Reverse sequence to restore service.
L-O L-O-C L-O L-O-C To transfer load from interrupter A to interrupter B:
1. Proceed from normal positions with operations as in 1

through 4 above.
2. Turn key A-1 in L-O-C interlock and key A-2 in L-O interlock on
interrupter A to lock open. Keys A-1 and A-2 are now free.
3. Insert key A-1 in L-O-C interlock and key A-2 in L-O interlock
A 1
on interrupter B and turn to unlock. Keys A-1 and A-2 are now
L-O
held.
4. Close interrupter B.
5. Turn key A-1 in L-O-C interlock on interrupter B to lock closed.
Key A-1 is free and key A-2 is held.
6. Insert key A-1 in L-O interlock on breaker and turn to unlock.
Breaker and interrupter A are shown in closed position. Interrupter B is Key A-1 is now held.
shown in open position. Key A-1 is held in breaker interlock. Key A-2 is 7. Close breaker.
held in interrupter A interlock. Reverse sequence to restore service through interrupter A.
Scheme 31 Scheme 32 (Continued)
To prevent operation (closed, open, or closed) of interrupter switch
when breaker is closed. Permits the breaker to be serviced and
operated while the interrupter switch is locked open.
A B
A B
E E
A2 A-1
E
L-O L-C-O-C
A-1
E
L-C-O-C
A-2
L-C
E
A 1
L-O
E
Breaker and interrupter are shown in closed position, connected to line A 1

B. Key A-1 is held in breaker interlock.
L-O
To service breaker, proceed as follows:
1. Open breaker. Breaker, fuse compartment door, and interrupter are shown in closed
2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1 position, connected to line B. Key A-1 is held in breaker interlock and
is now free. key A-2 is held in interrupter interlock.
3. Insert key A-1 in L-C-O-C interlock on interrupter and turn to
unlock. Key A-1 is now held. To service breaker, proceed as follows:
5. Turn key A-1 in L-C-O-C interlock on interrupter to lock open. 1. Open breaker.
Key A-1 is now free. 2. Turn key A-1 in L-O interlock on breaker to lock open. Key A-1
6. Return key A-1 to breaker interlock and unlock for operation is now free.
of breaker during servicing. 3. Insert key A-1 in L-C-O-C interlock on interrupter and turn to
Reverse sequence to restore service through either line A or line B. 4. Open interrupter.
5. Turn key A-1 in L-C-O-C interlock on interrupter to lock open.
To transfer interrupter from line B to line A: Key A-1 is now free.
6. Return key A-1 to breaker interlock and unlock for operation of
1. Proceed from normal position with operations as in steps 1 breaker during servicing.
through 3 above. Reverse sequence to restore service through either line A or line B.
2. Open interrupter switch from line B and connect to line A.
3. Turn key A-1 in L-C-O-C interlock on interrupter to lock closed. To open fuse compartment door:
4. Insert key A-1 in L-O interlock on breaker and turn to unlock. 1. Proceed from normal position with operations 1 through 4
Key A-1 is now held. above.
5. Close breaker. 2. Turn key A-2 in L-O interlock on interrupter to lock open. Key A-
2 is now free.
Reverse sequence to restore service through line B. 3. Insert key A-2 in L-C interlock on fuse compartment door and
To transfer interrupter from line B to line A:

Scheme 32
1. Proceed from normal position with operations as in steps 1
To prevent operation (closed, open, or closed) of interrupter switch through 3 above.
when breaker is closed. To prevent opening fuse compartment door 2. Open interrupter switch from line B and connect to line A.
when the interrupter switch A is closed. To prevent closing interrupter 3. Turn key A-1 in L-C-O-C interlock on interrupter to lock closed.
switch until fuse compartment door is locked closed. Permits the Key A-1 is now free.
breaker to be serviced and operated while the interrupter switch is 4. Insert key A-1 in L-O interlock on breaker and turn to unlock.
locked open. Key A-1 is now held.
5. Close breaker.
Reverse sequence to restore service through line B.

Scheme 33
To prevent opening of guard B with motor circuit closed. TO OPERATOR
Starting switch normally closed. Key A-1 is held in starting switch

E
interlock. Guard B (or door) is locked closed by means of type D SWITCH A 1
(detachable) interlock.
L-O W
1. Open starting switch. A2
2. Turn key A-1 in L-O interlock on switch to lock open. Key A-1 is
now free. E
A-1
3. Insert key A-1 in L-C interlock (type D) on guard B and turn to
L-C
4. Open guard. Service person can remove key A-2 and hold
until the service is complete. Thereby ensuring that the key
sequence cannot be reversed until the guard is locked
closed again.
GUARD B
Scheme 34
To prevent opening of guard B for a pre-determined time after TIME DELAY KEY RELEASE UNIT
removal of power.
SIGNAL LIGHT
Starting switch normally closed. Key A-1 is held in starting switch A 2 A-1
interlock. Guard B (or door) is locked closed by means of type D
(detachable) interlock.
1. Open starting switch. TO OPERATOR

2. Turn key A-1 in L-O interlock on switch to lock open. Key A-1 is E
now free. SWITCH A 1
3. Insert key A-1 in time delay key release unit (type TDKRU) and
L-O W
rotate to start the time delay action. A3
4. Signal light energized and key A-2 can be removed after the
prescribed time elapses. Key A-1 is now held. E
A-2
5. Insert key A-2 in L-C interlock (type D) on guard B and turn to
unlock. Key A-2 is now held. L-C
6. Open guard. Service person can remove key A-3 and hold
until the service is complete. Thereby ensuring that the key
sequence cannot be reversed until the service is complete
and the guard is locked closed again. GUARD B

Scheme 35 Scheme 35A
To prevent paralleling of any sources while allowing switching of the
loads to alternate sources. To prevent closing the generator breaker when the main breaker is
closed.
A B GENERATOR A Generator
A-1
B-1
L-O
A1 A B B1 G B-1
E E
A G
A 1 A-1
C
L-O L-O
M N
Breaker A is closed to supply load M. Breaker B is closed to supply load

N. Tie-Breaker C and generator breaker G are locked open. Key A-1 is
held in the L-O interlock on breaker A. Key B-1 is held in the L-O
interlock on breaker B. Tie-Breaker C cannot be closed unless either
breaker A or B is locked open. Generator breaker G cannot be closed M
unless breaker B is locked open. Tie-Breaker C interlock has an
apartment lock and can be unlocked for operation with either key A-1
or B-1. Generator breaker G interlock can be unlocked for operation Breaker A is closed to supply load M. Key A-1 is held in the L-O interlock
with key B-1 only. on breaker A. Generator breaker G is locked open and cannot be
closed until breaker A is locked open.
To transfer load N to breaker A, proceed as follows:
1. Open breaker B. To transfer load M to the generator, proceed as follows:
2. Turn key B-1 in L-O interlock on breaker B to lock open. Key B- 1. Open breaker A.
1 is now free. 2. Turn key A-1 in L-O interlock on breaker A to lock
3. Insert Key B-1 in L-O interlock on tie-breaker C and turn to open. Key A-1 is now free.
unlock. Key B-1 is now held. 3. Insert key A-1 in L-O interlock on breaker G and turn
4. Close tie-breaker C. to unlock. Key A-1 is now held.
4. Close breaker G.
Reverse sequence to restore service through breaker B. Load M can
be supplied through breaker B in a similar manner. Reverse sequence to restore service through breaker A.
To transfer load N to the generator, proceed as follows:

1. Open breaker B.
1 is now free.
3. Insert key B-1 in L-O interlock on generator breaker G and
turn to unlock. Key B-1 is now held.
4. Close generator breaker G.
Reverse sequence to restore service through breaker B.
To transfer loads M and N to the generator, proceed as follows:

1. Open breaker A.
2. Turn key A-1 in L-O interlock on breaker A to lock open. Key
A-1 is now free.
3. Open breaker B.
1 is now free.
5. Insert key A-1 in L-O interlock on tie-breaker C and turn to
6. Close tie-breaker C.
7. Insert key B-1 in L-O interlock on generator breaker G and
turn to unlock. Key B-1 is now held.
8. Close generator breaker G.
Reverse sequence to restore service through breakers A and B.
A-1 Note: This symbol represents an interlock with an apartment

B-1 lock. An apartment lock is a single cylinder that will accept
two different keys - but only one key at a time.
Scheme 36
To prevent paralleling of any sources while allowing switching of the loads to alternate sources.
GENERATOR A B GENERATOR
A-1
B-1
H L-O
A-1 A1 A B B1 G B-1
M N
Breaker A is closed to supply load M. Breaker B is closed to supply Key A-1 is now free.
load N. Tie-Breaker C and generator breakers G and H are locked 3. Insert key A-1 in L-O interlock on generator breaker H
open. Key A-1 is held in the L-O interlock on breaker A. Key B-1 is and turn to unlock. Key A-1 is now held.
held in the L-O interlock on breaker B. Tie-Breaker C cannot be 4. Close generator breaker H.
closed unless either breaker A or breaker B is locked open. Generator Reverse sequence to restore service through breaker A.
breaker G cannot be closed unless breaker B is locked open. Load N can be transferred to generator G using the B-1 key in a similar
Generator breaker H cannot be closed unless breaker A is locked manner.
open. Tie-Breaker C interlock has an apartment lock and can be
unlocked for operation with either key A-1 or B-1. Generator G To transfer loads M and N to generator H, proceed as follows:
breaker interlock can be unlocked for operation with key B-1 only. 1. Open breaker A.
Generator H breaker interlock can be unlocked for operation with Key 2. Turn key A-1 in L-O interlock on breaker A to lock open.
A-1 only. Key A-1 is now free.
3. Open breaker B.
To transfer load N to breaker A, proceed as follows: 4. Turn key B-1 in L-O interlock on breaker B to lock open.
1. Open breaker B. Key B-1 is now free.
2. Turn key B-1 in L-O interlock on breaker B to lock open. 5. Insert key B-1 in L-O interlock on tie-breaker C and turn
Key B-1 is now free. to unlock. Key B-1 is now held.
3. Insert Key B-1 in L-O interlock on tie-breaker C and turn 6. Close tie-breaker C.
to unlock. Key B-1 is now held. 7. Insert key A-1 in L-O interlock on generator breaker H
4. Close tie-breaker C. and turn to unlock. Key A-1 is now held.
Reverse sequence to restore service through breaker B. Load M can 8. Close generator breaker H.
be supplied through breaker B in a similar manner. Reverse sequence to restore service through breakers A and B.
To transfer load M to generator H, proceed as follows: Loads M and N can be transferred to generator G in a similar manner.
1. Open breaker A. Open breakers A & B, then utilize the A-1 key to unlock tie-breaker C
2. Turn key A-1 in L-O interlock on breaker A to lock open. and utilize the B-1 key to unlock generator breaker G.
A-1
B-1
Scheme 37
To prevent closing ground switch B under load and to enable To gain access to capacitor bank enclosure, proceed as
access to the capacitor bank enclosure only after the follows:
capacitor bank has been grounded and discharged.
1. Open breaker A.
CAPACITOR BANK 2. Turn key A-1 in L-O interlock on breaker A to lock
ENCLOSURE
3. Insert key A-1 in L-O interlock on ground switch B and
turn to unlock. Close ground switch B. Key A-1 is now
ACCESS
#2
A E held.
A-3
4. Turn key A-2 in L-C interlock on ground switch B to
ACCESS L-C lock closed. Key A-2 is now free.
#1
5. Insert key A-2 in L-C interlock (Type M2D) on capacitor
E E E
B bank enclosure access door #1 and turn to unlock.
A1 A-1 A2 W
A3 Key A-2 is now held and key A-3 is now free.
L-O L-O L-C
A-2
E 6. Open access door #1 to enter capacitor bank
L-C
enclosure.
7. Insert key A-3 in L-C interlock (Type D) on access door
#2 and turn to unlock. Key A-3 is now held.
Capacitor bank scheme without time delay. 8. Open access door #2 to enter capacitor bank
enclosure.
Breaker A is closed. Ground switch B is locked open. All
capacitor bank enclosure doors are locked closed. Key A-1 is Reverse sequence to restore service.
held in L-O interlock on breaker A. Key A-2 is held in L-C
interlock on ground switch B. Key A-3 is held in L-C interlock
(Type M2D) on access door #1.
Scheme 38
To prevent closing ground switch B under load and to enable To gain access to capacitor bank enclosure, proceed as follows:
access to the capacitor bank enclosure only after the capacitor
bank has been grounded and discharged.
1. Open breaker A.
CAPACITOR BANK
2. Turn key A-1 in L-O interlock on breaker A to lock open.
ENCLOSURE Key A-1 is now free.
3. Insert Key A-1 in initiating lock on TDKRU. Turn key to start
ACCESS
time delay action.

#2
A E
A-4 4. Signal light energized and key A-2 can be removed
after the prescribed time period. Key A-1 is now held.
L-C
E E E
B ACCESS
#1 5. Insert key A-2 in L-O interlock on ground switch B and turn
A1 A-2 A3
to unlock. Close ground switch B. Key A-2 is now held.
L-O L-O L-C A4
W 6. Turn key A-3 in L-C interlock on ground switch B to lock
E
A-3 7. Insert key A-3 in L-C interlock (Type M2D) on capacitor
SIGNAL LIGHT L-C
bank enclosure access door #1 and turn to unlock. Key
A-3 is now held and key A-4 is now free.
A 2 A-1
TIME DELAY KEY RELEASE UNIT 8. Open access door #1 to enter capacitor bank
enclosure.
9. Insert key A-4 in L-C interlock (Type D) on access door #2
Capacitor bank scheme with time delay. and turn to unlock. Key A-4 is now held.
10. Open access door #2 to enter capacitor bank
Breaker A is closed. Ground switch B is locked open. All capacitor enclosure.
bank enclosure doors are locked closed. Key A-1 is held in L-O
interlock on breaker A. Key A-2 is held in Time Delay Key Release Reverse sequence to restore service.
Unit (TDKRU). Key A-3 is held in L-C interlock on ground switch B.
Key A-4 is held in L-C interlock (Type M2D) on access door #1.
Scheme 39 Scheme 40
To prevent improper maintenance bypass of Uninterruptible To prevent improper maintenance bypass of Uninterruptible
Power Supply. Power Supply.
SKRU
SKRU
KIRK
KIRK A1
A1 E
B-1
UPS SYSTEM MAINTENANCE UPS SYSTEM MAINTENANCE
OUTPUT
E BYPASS OUTPUT BYPASS
BREAKER BREAKER BREAKER BREAKER
(NC) (NO) (NC) A A1 A-1 B (NO)
A B1 A-1 B B-1 B1
W W
CRITICAL LOAD CRITICAL LOAD
Solenoid Key Release Unit (SKRU) shown with A-1 Key held Solenoid Key Release Unit (SKRU) shown with A-1 Key held
captive. UPS output breaker A is closed supplying the critical captive. UPS output breaker A is closed supplying the critical
load through the UPS. Key B-1 is held captive in the L-O load through the UPS. A second key A-1 is held captive in the
interlock on breaker A. Maintenance bypass breaker B cannot L-O interlock on breaker A. Key B-1 is held captive in L-O
be closed until the UPS is placed in bypass mode, sending a interlock on maintenance bypass breaker B. Maintenance
signal to the SKRU allowing release of key A-1. The SKRU has an bypass breaker B cannot be closed until the UPS is placed in
apartment lock that will accept either key A-1 or B-1. bypass mode, sending a signal to the SKRU allowing release of
SKRU key A-1.
To supply critical load through the maintenance bypass
breaker, proceed as follows: To supply critical load through the maintenance bypass
1. Place the UPS in bypass mode. breaker, proceed as follows:
2. Upon receipt of the proper signal, key A-1 in SKRU can 1. Place the UPS in bypass mode.
be turned changing status of SKRU internal contacts 2. Upon receipt of the proper signal, key A-1 in SKRU can
and releasing key A-1. be turned changing status of SKRU internal contacts
3. Insert key A-1 in L-O interlock on maintenance bypass and releasing key A-1.
breaker B and turn to unlock. 3. Insert key A-1 in L-O interlock on maintenance bypass
4. Close maintenance bypass breaker B. Key A-1 is now breaker B and turn to unlock.
held. 4. Close maintenance bypass breaker B. Key A-1 is now
5. Open UPS output breaker A. held. Key B-1 is now free.
6. Turn key B-1 in interlock on UPS output breaker A to 5. Open UPS output breaker A.
lock open. Key B-1 is now free. 6. Insert key B-1 in interlock on UPS output breaker A and
7. Insert key B-1 in SKRU and turn to return the SKRU turn to lock open. Key B-1 is now held. Key A-1 is now
internal contacts to the original position. Key B-1 is free.
now held in the SKRU. 7. Insert key A-1 in SKRU and turn returning the SKRU
internal contacts to the original position. Key A-1 is
Reverse sequence to restore equipment to original condition. now held in the SKRU.
Note: Refer to UPS manufacturer's operation and maintenance Reverse sequence to restore equipment to original condition.
manual for instructions regarding transferring the load to the
UPS maintenance bypass source. Persons not familiar with the Note: Refer to UPS manufacturer's operation and maintenance
operation of the UPS system should not attempt to change the manual for instructions regarding transferring the load to the
position the above devices. UPS maintenance bypass source. Persons not familiar with the
operation of the UPS system should not attempt to change the
position of the above devices.
A-1 Note: This symbol represents an interlock with an apartment
B-1 lock. An apartment lock is a single cylinder that will accept
two different keys - but only one key at a time.
Scheme 41
To prevent opening any access doors of an electrostatic precipitator until all power supplies are de-energized and properly grounded.
CONTROL CIRCUIT BREAKERS
E E
A1 A2 A2
L-O L-O L-C

TRANSFER PANEL
SINGLE SINGLE
G-1 G-2 G-3 G-4 INSERTION OF
T/R SWITCH T/R SWITCH
ALL GROUND
SWITCH KEYS
G-6 G-7 G-8 G-9 REQUIRED
E E TO RELEASE
HV A-1 HV A-2 ANY ACCESS
POSITION POSITION D1 D1 D1 DOOR KEYS.
L-C L-O
TR TR D1 D1 D1 D1
E
GROUND E
GROUND
G1 A1
POSITION POSITION D1 D1 D 1 ACCESS DOOR
L-C L-O KEYS NORMALLY

HELD IN
D1 D1 TRANSFER PANEL.
E E
D-1 D-1 D-1 ACCESS DOOR KEYS ARE
RETAINED WHEN DOOR/HATCH
L-C L-C L-C IS IN THE OPEN POSITION.
ACCESS DOORS
Precipitator scheme with single output transformer rectifiers.
All main breakers in ESP control room are closed to supply all transformer rectifiers. All A keys (A-1, A-2, A-3, etc.) are held in L-O interlocks on the
breakers. All transformer rectifiers are locked in the ON position. All G keys (G-1, G-2, etc.) are held in L-C interlocks on the ground position of the
transformer rectifiers. All access doors are locked closed and all access door keys are held in the transfer panel (key exchange box).
To open all access doors:

1. Open breaker A-1.
2. Turn key A-1 in L-O interlock to lock breaker in the open position. Key A-1 is now free.
3. Lock open all other breakers and free all A keys (A-2, A-3, A-4, etc.).
4. Insert all A keys in the L-C interlocks on the HV position of each TR. Turn A keys to unlock. All A keys are now held.
5. Rotate all TR handles to the ground position.
6. Turn all G keys (G-1, G-2, G-3, etc.) in L-C interlocks of each TR to lock all TR handles in the ground position. All G keys are now
free.
7. Insert all G keys in the transfer panel (key exchange box) and turn. All G keys are now held.
8. Turn and remove the D-1 keys from the transfer panel. Note: D-1 keys are secondary keys and cannot be removed until all
primary keys (G keys) are inserted and turned.
9. Insert the D-1 keys in each access door interlock and turn to unlock. The D-1 keys will remain held in each access door interlock
as long as the door is open.
To restore service, close and lock all access doors, return all D-1 keys to the transfer panel and reverse the above sequence.
The scheme above represents basic guidelines regarding the proper interlock sequence for an Electro-Static Precipitator. The equipment that
comprises an E.S.P., or Baghouse can vary depending upon the manufacturer and age of the equipment. Let us know your specific needs and we
will be glad to provide a free proposal without obligation.
Scheme 42
To allow operation of dual output transformer rectifiers with one field removed from service and to prevent opening any access doors of an
electrostatic precipitator until all power supplies are de-energized and properly grounded.
CONTROL CIRCUIT BREAKERS
E E
A1 A2 A3
E E
A1 A2 A3
L-O L-O L-C
TO
REENERGIZE
ONE SIDE
DUAL OUTPUT ONLY DUAL OUTPUT
T/R SWITCH T/R SWITCH TRANSFER PANEL
HV A-1
E E
TR2, TR3, Etc.
A-1 HV G-1 G-1 G-2 G-2
POSITION POSITION Similar to TR1 INSERTION OF
W ALL GROUND
L-C A1 L-C Supplied by breakers SWITCH KEYS
G-6 G-6 G-7
TR1 G-1
E
TR1 A-2, A-3, A-4, etc. G-7

REQUIRED
TO RELEASE
ANY ACCESS
GROUND E TRANSFER E
GROUND The quantity of TRs D1 D1 D1 DOOR KEYS.
G1 G1
POSITION POSITION will vary depending
L-C L-C upon your system.
D1 D1 D1 D1
ACCESS DOOR
D1 D1 D 1 KEYS NORMALLY
HELD IN
TRANSFER PANEL.
D1 D1
All
D 1 E D 1 E Access Additional
Doors
as
L-C L-C L-C Required
All ESP Access Doors, Hopper Doors, Etc.

ACCESS DOOR KEYS ARE RETAINED WHEN DOOR/HATCH IS IN THE OPEN POSITION.
Precipitator scheme with dual output transformer rectifiers.
breakers (note: one A key is held in a transfer block on each TR). All transformer rectifiers are locked in the ON position. All G keys (G-1, G-2, etc.) are
held in L-C interlocks on the ground position of the transformer rectifiers. All access doors are locked closed and all access door keys are held in the
transfer panel (key exchange box).
To ground one field of TR1, proceed as follows:

2. Turn key A-1 in L-O interlock to lock breaker in open position. Both A-1 keys are now free.
3. Insert one A-1 key in L-C interlock on HV position of the field to be removed from service. Turn key to unlock. Key A-1 is now held.
4. Rotate TR1 handle to ground position.
5. Turn key G-1 in L-C interlock locking the TR handle in the ground position. Key G-1 is now free.
6. Insert key G-1 in the transfer block and turn. Key G-1 is now held and key A-1 is free.
7. Insert key A-1 in L-O interlock on the breaker and turn to unlock. Both A-1 keys are now held.
8. Close breaker A-1.
Other fields can be removed from service in the same manner. Reverse sequence to restore service.

2. Turn key A-1 in L-O interlock to lock breaker in the open position. Both A-1 keys are now free.
4. Insert all A keys in the L-C interlocks on the HV position of each TR. Turn A keys to unlock. All A keys are now held.
6. Turn all G keys (G-1, G-2, G-3, etc.) in L-C interlocks of each TR to lock all TR handles in the ground position. All G keys are now free.
8. Turn and remove the D-1 keys from the transfer panel. Note: D-1 keys are secondary keys and cannot be removed until all primary keys (G
keys) are inserted and turned.
9. Insert the D-1 keys in each access door interlock and turn to unlock. The D-1 keys will remain held in each access door interlock as long as
the door is open.
The scheme above represents basic guidelines regarding the proper interlock sequence for an Electro-Static Precipitator. The equipment that comprises an E.S.P., or
Baghouse can vary depending upon the manufacturer and age of the equipment. Let us know your specific needs and we will be glad to provide a free proposal without
obligation.
Scheme 42A
E E E E
A 1 A 1 A 2
A 2
L-O K 1 W L-O K 2 W
K 1 W K 2 W
Transfer Transfer
E E
K 1 K 2
G 1 W G 2 W
Transfer Transfer
E E E E
K 1 K 1 K 2 K 2 TR3, TR4, etc. supplied
HV
Position TO
HV HV
Position
HV by breakers A-3, A-4, etc.
L-C L-C Position L-C L-C Position
REENERGIZE
ONE SIDE
ONLY Similar to A-1, A-2 at left.
TR1 TR1 TR2 TR2
E E E E The quantity of TR's will
G 1 G 1 G 2 G 2
vary depending upon
Ground
Position L-C L-C
Ground Ground
Position L-C L-C
Ground your system.
Position Position
All G Keys from TR's
Key Exchange Box on ESP Roof All ESP Access Doors, Hopper Doors, Etc.
Additional
G 1 G 1 G 2 G 2 G 3 G 3 G 4 as All G Keys must be
All
Required inserted before any D
D 1 E D 1 E Access
Additional
keys can be released. as
Doors Required
D 1 D 1 D 1 D 1 D 1 D 1 D 1
L-C L-C L-C
To Access Door Locks
breakers. All transformer rectifiers are locked in the ON position. All K keys (K-1, K-2, etc.) are held in transfer blocks. All G keys (G-1, G-2, etc.) are held
in L-C interlocks on the ground position of the transformer rectifiers. All access doors are locked closed and all access door keys are held in the
transfer panel (key exchange box).
To ground one field of TR1, proceed as follows:

2. Turn key A-1 in L-O interlock to lock breaker in open position. Key A-1 is now free.
3. Insert key A-1 in the three-cylinder transfer block and turn. Key A-1 is now held and both K-1 keys are free.
4. Insert one K-1 key in L-C interlock on HV position of the field to be removed from service. Turn key to unlock. Key K-1 is now held.
5. Rotate TR handle to ground position.
6. Turn key G-1 in L-C interlock locking the TR handle in the ground position. Key G-1 is now free.
7. Insert key G-1 in the two-cylinder transfer block and turn. Key G-1 is now held and key K-1 is now free. Insert key K-1 in the three cylinder
transfer block and turn. Both K-1 keys are now held and the A-1 key is free.
8. Insert key A-1 in L-O interlock on the breaker and turn to unlock. Key A-1 is now held.
9. Close breaker A-1.
Other fields can be removed from service in the same manner. Reverse sequence to restore service.

4. Insert all A keys in their respective three-cylinder transfer blocks and turn. All A keys are now held and all K keys (K-1, K-2, K-3, etc.) are free.
5. Insert all K keys in the L-C interlocks on the HV position of each TR. Turn K keys to unlock. All K keys are now held.
7. Turn all G keys (G-1, G-2, G-3, etc.) in L-C interlocks of each TR to lock all TR handles in the ground position. All G keys are now free.
9. Turn and remove the D-1 keys from the transfer panel. Note: D-1 keys are secondary keys and cannot be removed until all primary keys (G
keys) are inserted and turned.
10. Insert the D-1 keys in each access door interlock to be opened and turn to unlock. The D-1 keys will remain held in each access door
interlock as long as the door is open.
The scheme above represents basic guidelines regarding the proper interlock sequence for an Electro-Static Precipitator. The equipment that comprises an E.S.P., or
Baghouse can vary depending upon the manufacturer and age of the equipment. Let us know your specific needs and we will be glad to provide a free proposal without
obligation.
Scheme 42B
Breaker in ESP Control Room Breaker in ESP Control Room Breaker in ESP Control Room
E E
A 1 A 2
L-O L-O L-O
TR1 TR2 Additional

A- 1 E A- 1 E A- 2 E A- 2 E as
A-3, A-4, Etc, TR's Required
HV HV
L-C L-C L-C Position L-C
Position
North
Splitter Switch
South North
Side
Splitter Switch South Similar to A-1, A-2
Side Side Side
Ground Ground
E E E E
N T
Position
S T N T
Position S T The quantity of TR's
E E E
will vary depending upon
G 1 G 1 E G 2 G 2
your system.
L-C L-C L-C L-C
All NT & ST Keys from TR's
E E E E Additional
G 1 G 2 G 3 G 4 as
Add'tl Add'tl Required
W W W W as as
A 1 A 2 A 3 A 4
Required Required
Transfer Transfer
Key Exchange Box on ESP Roof Key Exchange Box on ESP Roof Key Exchange Box on ESP Roof
North Chamber Key Exchange Box on ESP Roof South Chamber

Additional Additional
N T N T N T N T as S T S T S T S T as
Required Required
D N D N D N D N D S D S D S D S
All All
Additional
D N E D S E Access Access
as
To Access DN Door Locks To Access DS Door Locks Doors Doors
Required
DN DN
L-C L-C or
DS
or
DS
To Access Both Chambers (North & South). L-C L-C
breakers. All TR splitter switches are locked in the ON position. All G keys (G1, G2, etc), NT and ST keys are held in the L-C interlocks on the ground
position of the TR splitter switches. An additional A key for each main breaker is held in the transfer panel (key exchange box). All access doors are
locked closed and all access door keys (DN & DS) are held in the transfer panel.
To access both "North" and "South" chambers:

4. Insert all A keys in their respective L-C interlocks on the "South" side of each TR splitter switch and turn to unlock. All A keys are now held.
5. Rotate each TR "South" side splitter switch handle to the ground position.
6. Turn the ST key in each L-C interlock locking each switch handle in the ground position. All ST and "South" side G keys are now free.
7. Insert all "South" side G keys (G1, G2, etc.) into the transfer panel and turn to release all A keys. The G keys are now held.
8. Remove all A keys and insert each key in the respective L-C interlocks on the "North" side of each TR splitter switch and turn to unlock. All A keys
are now held.
9. Rotate each TR "North" side splitter switch handle to the ground position.
10.Turn the NT key in each L-C interlock locking each switch handle in the ground position. All NT and "North" side G keys are now free.
11.Insert all NT and ST keys in the transfer panel to release all DN and DS keys. Turn and remove the DN and DS keys from the transfer panel.
Note: DN and DS keys are secondary keys and cannot be removed until all primary keys (NT and ST keys) are inserted and turned.
12.Insert the DN and DS keys in each access door interlock to be opened and turn to unlock. The DN and DS keys will remain held in each access
door interlock as long as the door is open.
To restore service to both chambers, close and lock all access doors, return all DN and DS keys to the transfer panel and reverse the above
sequence.
Continued Next Page

Scheme 42B
E E
A 1 A 2
L-O L-O L-O
TR1 TR2
Additional
A- 1 E A- 1 E A- 2 E A- 2 E as
HV HV
L-C L-C L-C Position L-C
Position
North
Splitter Switch
South North
Side
Splitter Switch
South
Side
Similar to A-1, A-2
Side Side
Ground Ground
E E E E
N T
Position
S T N T
Position S T The quantity of TR's
E E E
will vary depending upon
G 1 G 1 E G 2 G 2
your system.
L-C L-C L-C L-C
All NT Keys from TR's
E E E E Additional
G 1 G 2 G 3 G 4 as
W W W W as as
A 1 A 2 A 3 A 4
Required Required
Transfer Transfer
North Chamber Key Exchange Box on ESP Roof South Chamber

Additional Additional
N T N T N T N T as S T S T S T S T as
Required Required
D N D N D N D N D S D S D S D S
All All Additional

D N E D N E Access Access as
To Access DN Door Locks Doors Doors
Required
L-C L-C D N D N
To Access the North Chamber. L-C L-C
To access the "North" chamber:

4. Insert all A keys in their respective L-C interlocks on the "North" side of each TR splitter switch. All A keys are now held.
5. Rotate each TR "North" side splitter switch handle to the ground position.
6. Turn the NT key in each L-C interlock locking each switch handle in the ground position. All NT and "North" side G keys are now free.
7. Insert all "North" side G keys (G1, G2, etc.) into the transfer panel and turn to release all A keys. The G keys are now held.
8. Insert all A keys in their respective L-O interlocks on each main breaker and turn to unlock. The A keys are now held.
9. Close all main breakers to energize the TR "South" fields.
10.Insert all NT keys in the transfer panel to release all DN keys. Turn and remove the DN keys from the transfer panel. Note: DN keys are secondary
keys and cannot be removed until all primary keys (NT keys) are inserted and turned.
11.Insert the DN keys in each access door interlock to be opened and turn to unlock. The DN keys will remain held in each access door interlock as
long as the door is open.
To restore service to the "North" chamber, close and lock all access doors, return all DN keys to the transfer panel and reverse the above sequence. The
"South" chamber can be accessed in the same manner.
Continued Next Page

Scheme 42B
E E
A 1 A 2
L-O L-O L-O
TR1 TR2
Additional
A- 1 E A- 1 E A- 2 E A- 2 E as
HV HV
L-C L-C L-C L-C
Position Position
North
Splitter Switch
South North
Side
Splitter Switch
South
Side
Similar to A-1, A-2
Side Side
Ground Ground
E E E E
N T Position S T N T Position S T The quantity of TR's will
E E E
vary depending upon
G 1 G 1 E G 2 G 2
your system.
L-C L-C L-C L-C
E E E E Additional
G 1 G 2 G 3 G 4 as
W W W W as as
A 1 A 2 A 3 A 4
Required Required
Transfer Transfer
To Remove One Field from Service
To remove the TR1 "North" field from service, proceed as follows:

2. Turn key A-1 in L-O interlock to lock breaker in open position. Key A-1 is now free.
3. Insert key A-1 in the L-C interlock on the "North" side TR1 splitter switch. Turn the key to unlock splitter switch handle. Key A-1 is now held.
4. Rotate the TR1 "North" side splitter switch handle to the ground position.
5. Turn the NT key in the L-C interlock locking the switch handle in the ground position. The NT and G1 keys are now free.
6. Insert and turn the G1 key into the transfer panel to release the A-1 key. The G1 key is now held.
7. Insert the A-1 key in the L-O interlock on the main breaker and turn to unlock. Key A-1 is now held.
8. Close breaker A-1 to energize the TR1 "South" field.
To remove the TR1 "South" field from service and reenergize the TR1 "North" field, proceed as follows:
2. Turn key A-1 in the L-O interlock to lock breaker in the open position. Key A-1 is now free.
3. Insert key A-1 in the L-C interlock on the TR1 "South" side splitter switch. Turn the key to unlock the splitter switch handle. Key A-1 is now held.
4. Rotate the TR1 "South" side splitter switch handle to the ground position.
5. Turn the ST key in the L-C interlock locking the switch handle in the ground position. The ST and G1 keys are now free.
6. Insert the G1 key in the L-C interlock on the ground position of the TR1 "North" side splitter switch and turn the NT key to unlock. The NT and G1 keys
are now held.
7. Rotate the TR1 "North" side splitter switch handle to the ON position.
8. Turn the A-1 key in the L-C interlock on the TR1 "North" side splitter switch to lock the handle in the ON position. The A-1 key is now free.
9. Insert the A-1 key in the L-O interlock on the main breaker and turn to unlock. Key A-1 is now held.
10.Close breaker A-1 to energize the TR1 "North" field.
Other TR fields can be removed from service in the same manner. Reverse sequence to reenergize each field.
The scheme above represents basic guidelines regarding the proper interlock sequence for an Electro-Static Precipitator. The equipment that comprises
an E.S.P., or Baghouse can vary depending upon the manufacturer and age of the equipment. Let us know your specific needs and we will be glad to
provide a free proposal without obligation.
Scheme 43
To prevent opening any rectifier enclosure door while the Breaker A is normally closed. Key A-1 is held in the L-O interlock on
rectifier is operating. breaker A. Keys A-2, A-3, and A-4 are held in L-C interlock (Type
M2D) on rectifier enclosure access doors #1, #2 and #3
respectively. All rectifier enclosure access doors are locked closed.
A A 1
E W
A 2
W
A 3
W
A 4
To gain access to the rectifier enclosure, proceed as follows:
L-O
E
A-1
E
A-2
E
A-3 1. Open Breaker A.
Rectifier L-C L-C L-C
2. Turn key A-1 to lock the breaker in the open position. Key A-1
Transformer
is now free.
3. Insert key A-1 in L-C interlock (Type M2D) on access door #1
Door 1 Door 2 Door 3
and turn to unlock.
4. Open access door #1 to enter the rectifier enclosure. Key A-1
Door 4
E
is now held and key A-2 is free.
A-4
5. Insert key A-2 in L-C interlock (Type M2D) on access door #2
L-C
and turn to unlock.
Rectifier 6. Open access door #2. Key A-2 is now held and key A-3 is free.
Enclosure 7. Insert key A-3 in L-C interlock (Type M2D) on access door #3
To
Neg Bus
and turn to unlock.
8. Open access door #3. Key A-3 is now held and key A-4 is free.
To
DC Swgr 9. Insert key A-4 in L-C interlock (Type D) on access door #4 and
turn to unlock.
10. Open access door #4. Key A-4 is now held.
Simple rectifier scheme with daisy chained door lock Reverse sequence to restore service.
arrangement. Any quantity of rectifier access doors can be
accommodated. Note: As an additional precaution, the Type D and M2D door
interlocks can be supplied with auxiliary contacts wired to the
breaker trip circuit.
Scheme 43A
To prevent opening any rectifier enclosure door while the Breaker A is normally closed. Key A-1 is held in the L-O interlock on
rectifier is operating. breaker A and supervisory key S-1 is retained by a supervisor. All A-
S 1 Supervisory 2 keys are held in the transfer interlock. All rectifier enclosure
Key E W W W W
access doors are locked closed.
Transfer
W A-1 A 2 A 2 A 2 A 2
S-1
A
E
A 1
L-O
To gain access to the rectifier enclosure, proceed as follows:
Rectifier
Transformer 1. Open Breaker A.
2. Insert supervisory key S-1 into L-O interlock on Breaker A and
turn key A-1 to lock the breaker in the open position. Key S-1 is
L-C
L-C
L-C
A-2 A-2 A-2

now held and key A-1 is free.
E E E
3. Insert key A-1 in transfer interlock and turn. Key A-1 is now held
Door 1 Door 2 Door 3 and A-2 keys are free.
E
4. Insert A-2 keys in the L-C interlocks (Type D) on rectifier access
Door 4 A-2 doors.
L-C 5. Open the rectifier access doors to enter the rectifier
enclosure. The A-2 keys are held in each door interlock as
Rectifier
long as the door is open.
Enclosure
To
Neg Bus To
DC Swgr Reverse sequence to restore service.
Simple rectifier scheme allowing doors to be opened in any

order. Supervisory key required for initial operation of breaker
interlock. Any quantity of rectifier access doors can be Note: As an additional precaution, the Type D door interlocks can
accommodated. be supplied with auxiliary contacts wired to the breaker trip circuit.
Scheme 44 Scheme 45
To prevent opening any rectifier enclosure door while the rectifier is
To prevent opening any rectifier enclosure door while the operating and to prevent opening the negative disconnect switch
rectifier is operating. under load.
E E
A 2 A-2
E E
A 2 A-2 L-O
W
D 1
A
L-O Load Break Switch In E
W Rectifier Transformer
D 1
A A- 1
E Primary Circuit D 1
W D-1
Load Break Switch In E
L-C
Rectifier Transformer
E W D-1 L-C
A- 1 Primary Circuit D 1 Rectifier W
Transformer
D 1 Rectifier
Door Lock
L-C
L-C
Rectifier W W
Transformer
D 1 Rectifier D 1 E
Door Lock
Rectifier D-1
W
W N 1
D 1 L-C
E
Rectifier D-1 Transfer
Rectifier
Transfer Door Lock
L-C
E
Rectifier
Door Lock D-1
Rectifier
Rectifier Doors
Doors L-C
E N Neg Disc
Rectifier
Switch Door Lock
D-1 E
N-1
L-C
L-C E
Rectifier
D-1
Door Lock
To L-C
Neg Bus
E
E B A 1
Rectifier
Door Lock
D-1 DC Main Typical Rectifier

Breaker L-O Door Interlocks
A 1
E B L-C
To
(Variable Qty)
DC Main Neg Bus

Rectifier
L-O Breaker Door Lock To DC Feeder
Breakers
Typical Rectifier
To DC Feeder Door Interlocks
(Variable Qty)
Breakers Rectifier with incoming load break switch, DC output breaker and
negative disconnect switch. Any quantity of rectifier access doors
can be accommodated.
Rectifier with DC output breaker. Any quantity of rectifier
access doors can be accommodated.
Load break switch A, DC main breaker B and negative disconnect
Load break switch A and DC main breaker B are normally switch N are normally closed. Key A-1 is held in the L-O interlock
closed. Key A-1 is held in the L-O interlock on breaker B. Key A- on breaker B. Key A-2 is held in the L-O interlock on load break
2 is held in the L-O interlock on load break switch A. All D-1 switch A. Key N-1 and all D-1 keys are held in the transfer interlock.
keys are held in the transfer interlock. All rectifier enclosure All rectifier enclosure access doors are locked closed.
access doors are locked closed.
1. Open breaker B.
1. Open breaker B. 2. Turn key A-1 to lock the breaker in the open position. Key A-1
2. Turn key A-1 to lock the breaker in the open position. Key is now free.
A-1 is now free. 3. Insert key A-1 in L-C interlock on load break switch A and turn
3. Insert key A-1 in L-C interlock on load break switch A and to unlock.
turn to unlock. 4. Open load break switch A. Key A-1 is now held.
4. Open load break switch A. Key A-1 is now held. 5. Turn key A-2 in L-O interlock on load break switch A to lock the
5. Turn key A-2 in L-O interlock on load break switch A and load break switch in the open position. Key A-2 is now free.
6. Insert key A-2 in the transfer interlock and turn. Key A-2 is now
turn to lock the load break switch in the open position.
held. All D-1 keys and key N-1 are now free.
7. Insert D-1 keys in the L-C interlocks (Type D) on rectifier access
6. Insert key A-2 in the transfer interlock and turn. Key A-2 is
doors.
now held and D-1 keys are free. 8. Open the rectifier access doors to enter the rectifier
7. Insert D-1 keys in the L-C interlocks (Type D) on rectifier enclosure. The D-1 keys are held in each door interlock as
access doors. long as the door is open.
8. Open the rectifier access doors to enter the rectifier 9. Insert key N-1 in L-C interlock on the negative disconnect
enclosure. The D-1 keys are held in each door interlock as switch N and turn to unlock.
long as the door is open. 10. Open negative disconnect switch N. Key N-1 is now held.
Reverse sequence to restore service. Reverse sequence to restore service.

Scheme 45A
To prevent opening any rectifier enclosure door while the Incoming breaker A, DC main breaker B and negative
rectifier is operating and to prevent opening the negative disconnect switch N are normally closed. Key A-1 is held in
disconnect switch under load. the L-O interlock on breaker A. Key A-2 is held in the L-O
interlock on breaker B. Key N-1 and all D-1 keys are held in the
transfer interlock. All rectifier enclosure access doors are
locked closed.
E
A-1
E
A-2
A 1
E A Incoming
Breaker
1. Open breaker A.
W E
D 1 D-1
L-O
2. Turn key A-1 in L-O interlock on breaker A to lock the
L-C
Rectifier W breaker in the open position. Key A-1 is now free.
Transformer
D 1
Rectifier
Door Lock
W 3. Open breaker B.
D 1
E
Rectifier
D-1
D 1
W 4. Turn key A-2 in L-O interlock on breaker B to lock the
L-C
breaker in the open position. Key A-2 is now free.
W
Rectifier
N 1 Door Lock
Transfer
5. Insert keys A-1 and A-2 in the transfer interlock and turn.
E Keys A-1 and A-2 are now held. All D-1 keys and key N-1
D-1 are now free.
L-C
Rectifier
N Neg Disc Doors
Rectifier
6. Insert D-1 keys in the L-C interlocks (Type D) on rectifier
Switch Door Lock
E access doors.
N-1
E
L-C
D-1 7. Open the rectifier access doors to enter the rectifier
L-C enclosure. The D-1 keys are held in each door interlock
as long as the door is open.
E Rectifier
B A 2
Door Lock
DC Main
8. Insert key N-1 in L-C interlock on the negative disconnect
Typical Rectifier
To Breaker L-O Door Interlocks switch N and turn to unlock.
Neg Bus (Variable Qty)
9. Open negative disconnect switch N. Key N-1 is now held.

To DC Feeder
Breakers
Rectifier with incoming breaker, DC output breaker and

negative disconnect switch. Any quantity of rectifier access Reverse sequence to restore service.
doors can be accommodated.
Kirk Key Interlock Company has been manufacturing trapped key interlocks and interlocking
systems since 1932. Since then, our interlocks have been instrumental in protecting personnel
and equipment and continue to be an important part of process safety worldwide. Kirk Key
products include mechanical and electro-mechanical interlocks, access interlocks, transfer blocks
and panels, cam locks, and our newest product line, Eagle Series valve interlocks. Our interlocks
are offered in standard duty, medium duty, and heavy duty series; each series offering an
increased level of durability.
Proper application of KIRK interlocks guarantees that a sequential pattern is followed for each
step of a prescribed sequence. KIRK key interlock systems are designed and configured to each
users requirements and revolve around a key or keys that an operator must use at each step in
the sequence.
Most manufacturers provide trapped key interlock provisions on their equipment. With Kirk
Key's wide range of components, it is possible to quickly design and supply an interlock system
that is custom designed to your specific physical requirements. If you need one key, one lock, or
an entire system, Kirk Key is ready to help.
Trapped key interlocking is accepted by standards, safety, and insurance authorities throughout
the world as the most reliable and cost effective way of guarding against operator error and
hazardous energy. If you are concerned about preserving safety throughout your sequential
operations, let Kirk Key Interlock Company fulfill your process safety needs with a customized
trapped key interlocking system for your project or operation.
For more information concerning any schemes in this book, or for help in configuring a custom
interlock system, please contact any one of our Inside Technical Sales Representatives.
Global Headquarters | 9048 Meridian Circle NW, North Canton, OH 44720

Phone 234.209.9301 | Fax 330.497.4400 | Toll Free 800.438.2442
sales@kirkkey.com
www.kirkkey.com

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APPLICATION SCHEME BOOK

Global Headquarters | 9048 Meridian Circle NW, North Canton, OH 44720

Interlock with key held.

Transfer interlock, Type T. Interlock with

Key released after time delay.

KIRK Key Interchange number

Interlock with Initiating key

Grounding Switch with Main Switch

Isolating Switches and Breaker

Isolating Switches and Breaker or Regulator with By-Pass Switch

Prevent Paralleling of Lines

Table of Contents Continued Next Page

Motor or Machinery Guard

Motor or Machinery Guard with Time Delay

Breakers and Generators

Capacitor Bank Access

Uninterrupted Power Sources

Table of Contents Continued Next Page

1. Obtain key A-2 from supervisor.

Reverse sequence to restore service.

L-O-C L-O Scheme 4

Reverse sequence to restore service. Reverse sequence to restore service.

NOTE: Electrical circuit is equivalent of Scheme 6.

L-O E L-O E L-O

Reverse sequence to restore service.

Reverse sequence to restore service.

Disconnects A and B are normally closed. Regulator is normally in

1. Operate regulator to neutral position.

Reverse sequence to restore service.

To transfer load from line A to line B:

To transfer load N to breaker A:

Reverse sequence to restore service.

M N Load M can be supplied through breaker B in a similar manner.

L-O-C L-O L-O L-O-C

L-O-C L-O-C A-2 A-4

Disconnect switches D and E and breakers A and B are closed. Breaker M N

To transfer load M from Breaker A to breaker B:

To transfer load M and N from breaker A and B to breaker C:

E F G 1. Close tie-breaker E as above.

M N P R To open rear access doors K-7, K-8 and K-9

D A-1 E A-2 F A-3 1. Close breaker D as per steps 1 to 4 above.

C D L-O A-1 A1 A-4 A-3 L-O

L-O A-1 A1 A-4 A-3 L-O

L-O L-O L-O

Under normal conditions breakers A and B are closed, disconnects C and

Reverse sequence to restore service. To isolate breaker B for servicing,

A1 C D B1 To isolate breaker C for servicing, proceed as follows:

Reverse sequence to restore service.

Breaker, fuse compartment door and interrupter are shown in closed

To service breaker, proceed as follows:

Reverse sequence to restore service.

Reverse sequence to restore service through interrupter A.

1. Proceed from normal positions with operations as in 1

Breaker and interrupter are shown in closed position, connected to line A 1

To transfer interrupter from line B to line A:

Reverse sequence to restore service through line B.

To prevent opening of guard B with motor circuit closed. TO OPERATOR

Starting switch normally closed. Key A-1 is held in starting switch

1. Open starting switch. TO OPERATOR

Reverse sequence to restore service.

Breaker A is closed to supply load M. Breaker B is closed to supply load

To transfer load N to the generator, proceed as follows:

Reverse sequence to restore service through breaker B.

To transfer loads M and N to the generator, proceed as follows:

Reverse sequence to restore service through breakers A and B.

A-1 Note: This symbol represents an interlock with an apartment

time delay action.

CRITICAL LOAD CRITICAL LOAD

CONTROL CIRCUIT BREAKERS

L-O L-O L-C

L-C L-O KEYS NORMALLY

To open all access doors:

TR1 A-2, A-3, A-4, etc. G-7

All ESP Access Doors, Hopper Doors, Etc.

Precipitator scheme with dual output transformer rectifiers.

To ground one field of TR1, proceed as follows: