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minimum number of cables required to safely ground transformer

1. Junior Member
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Jul 2018
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minimum number of cables required to safely ground transformer

4/0 grounded cable is rated at 43kA for 15cycles. What is the minimum number of cables per phase required to safely ground a 2500kVA 5.75%Z transformer on the 480V side?

A-1
B-2
C-3
D-4

Looking for help on this. XFMR fault current is 52,297 on the 480V side assuming 3phase? my guess is 2 cables per phase.

480*1.732 = 831.36
2500000 / 831.36 = 3007.12
3007.12 / 0.0575 = 52297

2. Wouldn't you need to know some more information about the system (i.e. what is the upstream protective device and clearing time, etc.)?

Originally Posted by samair99
4/0 grounded cable is rated at 43kA for 15cycles. What is the minimum number of cables per phase required to safely ground a 2500kVA 5.75%Z transformer on the 480V side?

A-1
B-2
C-3
D-4

Looking for help on this. XFMR fault current is 52,297 on the 480V side assuming 3phase? my guess is 2 cables per phase.

480*1.732 = 831.36
2500000 / 831.36 = 3007.12
3007.12 / 0.0575 = 52297