×
Follow Us
Results 1 to 3 of 3

Acceptable reading for a new grounding system

    #1
  1. Join Date
    Jun 2017
    Posts
    4
    Reputation

    Acceptable reading for a new grounding system

    In a general industrial application, what kind of reading is acceptable for a new grounding system?


    5 ohms

    10 ohms

    15 ohms

    25 ohms

    I thought the correct answer was no greater that .5 Ohms

  2. #2
  3. Kalbi_Rob's Avatar
    Kalbi_Rob is offline Experienced Member Pro Subscriber
    Join Date
    Feb 2018
    Location
    Richmond, VA
    Posts
    169
    Reputation
    Quote Originally Posted by rmr660 View Post
    In a general industrial application, what kind of reading is acceptable for a new grounding system?


    5 ohms

    10 ohms

    15 ohms

    25 ohms

    I thought the correct answer was no greater that .5 Ohms
    2008 NEC:
    250.56 Resistance of Rod, Pipe, and Plate Electrodes
    A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(A)(4) through (A)(8). Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart.


    IEEE 142 (Green Book) 3.3.4.6:
    For satisfactory lightning protection, substation grounding network resistance must
    not exceed 5 ohm; for large stations, lower values are desirable.


    IEEE 142 (Green Book) 4.1.3:
    Resistances in the 1 ohm to 5 ohm range are generally found suitable for industrial plant substations and buildings and large commercial installations. Special grounding considerations for Arctic conditions will not be addressed, but additional information is available in Gill, and Beck and Yu.

    The 25 ohm value noted in the NEC applies to the maximum resistance for a single
    electrode consisting of a rod, pipe, or plate. If a higher resistance is obtained for a single
    electrode, a second electrode of any of the types specified in the NEC is required. This
    should not be interpreted to mean that 25 ohm is a satisfactory resistance value for a
    grounding system.


    So, for Industrial and Large Commercial Installations, ground resistance shall be less than 5 ohms, all other times less than 25 ohms. Any specification can call for lower resistances, but not more. Thus many Utilities will call for Substations to be less than 1 ohm or even 0.5 ohms.

  4. #3
  5. Kalbi_Rob's Avatar
    Kalbi_Rob is offline Experienced Member Pro Subscriber
    Join Date
    Feb 2018
    Location
    Richmond, VA
    Posts
    169
    Reputation
    Quote Originally Posted by Kalbi_Rob View Post
    2008 NEC:
    250.56 Resistance of Rod, Pipe, and Plate Electrodes
    A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(A)(4) through (A)(8). Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart.


    IEEE 142 (Green Book) 3.3.4.6:
    For satisfactory lightning protection, substation grounding network resistance must
    not exceed 5 ohm; for large stations, lower values are desirable.


    IEEE 142 (Green Book) 4.1.3:
    Resistances in the 1 ohm to 5 ohm range are generally found suitable for industrial plant substations and buildings and large commercial installations. Special grounding considerations for Arctic conditions will not be addressed, but additional information is available in Gill, and Beck and Yu.

    The 25 ohm value noted in the NEC applies to the maximum resistance for a single
    electrode consisting of a rod, pipe, or plate. If a higher resistance is obtained for a single
    electrode, a second electrode of any of the types specified in the NEC is required. This
    should not be interpreted to mean that 25 ohm is a satisfactory resistance value for a
    grounding system.


    So, for Industrial and Large Commercial Installations, ground resistance shall be less than 5 ohms, all other times less than 25 ohms. Any specification can call for lower resistances, but not more. Thus many Utilities will call for Substations to be less than 1 ohm or even 0.5 ohms.
    ANSI/BICSI 002: Data Center Design and Implementation Best Practices

    Recommends 5 Ohms Maximum, but recommends 3 Ohms for Class F2 & F3 Data Centers, and 1 Ohm for Class F4 Data Centers

Subscribe

Login or register to leave a reply!


Share this thread

Related Topics

  1. Doble Testing a Bushing: C2 reading higher than nameplate
    By Bob_Woodward in forum Electrical Testing Talk
    Replies: 8
    Last Post: April 2, 2020, 11:49 AM
  2. where does acceptable freq deviation come from?
    By madsenate in forum NETA Level 3 Exam
    Replies: 1
    Last Post: September 1, 2018, 03:38 PM
  3. Replies: 2
    Last Post: May 20, 2018, 08:15 AM
  4. Layering Arc Flash Clothing, Is It Acceptable?
    By SecondGen in forum Safety and Arc Flash Talk
    Replies: 1
    Last Post: May 20, 2018, 07:53 AM
  5. Contact resistance tester doesn't display any reading
    By lnides in forum Electrical Testing Talk
    Replies: 7
    Last Post: February 2, 2016, 11:53 PM

Tags for this Thread



Related Content


Follow us


Explore TestGuy


NETA Certification Training


NICET Electrical Power Testing


Help and Support