GEC size for 400 amp service

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Dennis Alwon

Dennis Alwon

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Did you read the notes
electrofelon said:
Now I am confused, why would you double it? I thought you were agreeing that you size it based on one set?
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Notes to 250.66

Notes:
1. If multiple sets of service-entrance conductors connect directly to a
service drop, set of overhead service conductors, set of underground
service conductors, or service lateral, 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.
2. Where there are no service-entrance conductors, the grounding
electrode conductor size shall be determined by the equivalent size of
the largest service-entrance conductor required for the load to be
served.
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Dennis Alwon

Dennis Alwon

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Rick 0920 said:
You do base it on one set. one 3/0 is 167,800 cm. 167,800 x 2 = 335,600 cm. T. 250.66 over 3/0 through 350 MCM requires a #2 GEC
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No you base it on one wire from each set so if you had one set at 3/0 and the other at 2/0 then you would add the cm for the 3/0 to the cm of the 2/0
 
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suemarkp

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But I think the 400 KCMIL in the mast trumps all of this. If you have an overhead service and condcctors from mast to meter to emergency disconnect to service disconnect and used different size conductors between some of the jumps, the GEC is sized based on the largest. The service disconnect breaker on the smallest. All of those conductore are service entrance conductors.
 
Dennis Alwon

Dennis Alwon

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suemarkp said:
But I think the 400 KCMIL in the mast trumps all of this. If you have an overhead service and condcctors from mast to meter to emergency disconnect to service disconnect and used different size conductors between some of the jumps, the GEC is sized based on the largest. The service disconnect breaker on the smallest. All of those conductore are service entrance conductors.
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That is correct. I thought we had 2 scenarios going on here
 
mopowr steve

mopowr steve

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jjhoward said:
Yes, each transfer sw has a 200 amp breaker.

I like the sounds of this, Steve. I will look for the same from MH docs. Where in the code is this supported?
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Ok guys,
I am just looking at my 2017 NEC Handbook next to my recliner.

If you have one, look at EXHIBIT 250.27. Although it shows a different size service mast conductor you can definitely see how the code is applied in relation to my response. Substitute the disconnects shown for service rated transfer switches in this thread and you get the jist.
 
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