NEC 250.66 Transformer Grounding Bar

[bcnj]

I am on a project where we are installing appx. 10 30kva-65kva transformers fed from one distribution panel. All transformers GEC will be tied into a single Grounding Bar that goes to building steel. Am I correct in saying the GEC sizing to the ground at should be the sum of all 10 GEC's to the transformers?


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[iwire]

Am I correct in saying the GEC sizing to the ground at should be the sum of all 10 GEC's to the transformers?

The common GEC will have to be 3/0.

 

[iwire]

See 250.30(A)(4).

 

[infinity]

I agree with Bob #3/0 is the minimum and the maximum required for a common grounding electrode that serves more than one transformer.

 

[jumper]

I think the applicable NEC section is 250.30(A)(6)(a)(1) and it would be a 3/0 CU or a 250kcmil AL.

Bob and Rob were quicker.

 

[iwire]

I think the applicable NEC section is 250.30(A)(6)(a)(1) and it would be a 3/0 CU or a 250kcmil AL.

Bob and Rob were quicker.

My code cite was from the 2008, yours may be more accurate.

 

[bcnj]

So even if I had 100 30kva transformers it will still be a 3/0?

I am thinking it 250.66 Note#1 is applicable.

Notes:
1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.


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[jumper]

So even if I had 100 30kva transformers it will still be a 3/0?

I am thinking it 250.66 Note#1 is applicable.

Notes:
1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.


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You would still end up with a 3/0

 

[augie47]

So even if I had 100 30kva transformers it will still be a 3/0?

I am thinking it 250.66 Note#1 is applicable.

Notes:
1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.


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Not applicable:

Is these transformers are fed from a distribution panel the secondaries would not be service conductors.
Note 1 applies to parallel condcutors (connected together at both ends)

 

[bcnj]

You are getting the size of the EGC based off of table 250.66. The table is labeled for service conductors.

Also, in theory, can someone argue that there is or is no limit to the amount you can place in a 3/0 wire?


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[don_resqcapt19]

You are getting the size of the EGC based off of table 250.66. The table is labeled for service conductors.

Also, in theory, can someone argue that there is or is no limit to the amount you can place in a 3/0 wire?


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ECGs are never sized using Table 250.66.

 

[bcnj]

May I ask what you are using if not that table??


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[iwire]

Also, in theory, can someone argue that there is or is no limit to the amount you can place in a 3/0 wire?

There is no case at all where the NEC requires more than a 3/0 GEC.

 

[infinity]

There is no case at all where the NEC requires more than a 3/0 GEC.

Which means that requiring no larger than #3/0 common grounding electrodes makes perfect sense.

 

[bcnj]

Except 250.66 Note 1

Notes:
1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.



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[bcnj]

Add the Circular Mils for each GEC and make sure your main GEC is equal or greater.


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[Smart $]

Except 250.66 Note 1

Notes:
1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.

You cannot exceed "Over 1100" or "Over 1750". :huh:

 

[jumper]

Add the Circular Mils for each GEC and make sure your main GEC is equal or greater.


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No.No.No.

That note says add up your hot conductors of each phase to size for a GEC.

The max being a 3/0.