GEC sizing

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amptech

amptech

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Indiana
I know according to 250.66(A) and (B) that the largest GEC to a rod, pipe or plate is #6 copper or #4 alum and to a CEE it is #4 copper. Where does table 250.66 apply? Just connections to metal water pipe and building steel?
 
amptech said:
I know according to 250.66(A) and (B) that the largest GEC to a rod, pipe or plate is #6 copper or #4 alum and to a CEE it is #4 copper. Where does table 250.66 apply? Just connections to metal water pipe and building steel?
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You would use Table 250.66 for example if you run a GEC from the service to a water pipe or structural metal building and from that point to a rod, pipe or plate, that portion of the GEC between the service equip. and the water pipe must be a full-size conductor per Table 250.66. ie: 3/0 awg ungrounded copper conductor would need a #2awg GEC. Then from the water pipe to the rod would not be required to be larger than #4awg for CEE or 6awg for rod.
 
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Little Bill said:
You would use Table 250.66 for example if you run a GEC from the service to a water pipe or structural metal building and from that point to a rod, pipe or plate, that portion of the GEC between the service equip. and the water pipe must be a full-size conductor per Table 250.66. ie: 3/0 awg ungrounded copper conductor would need a #2awg GEC. Then from the water pipe to the rod would not be required to be larger than #4awg for CEE or 6awg for rod.
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I see no problem with the logic, but a couple of problems with the numbers.
A 3/0 cu service conductor grounding electrode conductor according to 250.66 could be as small as #4 cu and the ground rod exception allows a reduction to a #6.
 
augie47 said:
I see no problem with the logic, but a couple of problems with the numbers.
A 3/0 cu service conductor grounding electrode conductor according to 250.66 could be as small as #4 cu and the ground rod exception allows a reduction to a #6.
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Augie,
I agree with the numbers, I should have been more careful with that. But my point was to use the Table to size the full size GEC for the portion from the service to the first point, the water pipe in this example. I was looking at the 3/0-350 line instead of 2/0-3/0 when I posted. Thanks for keeping me straight.
 
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