# Sizing a supply side or main bond with parallel conductors



## jar546 (Jul 29, 2019)

When you have to size a supply side bonding jumper as required in NEC 250.102, you would use Table 250.102(C)(1) which is based on the size of the largest ungrounded conductor.  The table is easy to use.  For example, if the largest ungrounded conductor entering the enclosure is 250MCM then you would need a 2awg copper bond wire.  If you had parallel conductors, such as 3 sets of 250MCM then you would add them together, 250x3=750MCM and the bond size would be a 2/0 copper.

BUT, what if you had a 400A service with 2 sets of 3/0 copper.  How would you do the math?


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## jar546 (Jul 30, 2019)

Any takers?  I'd like to get a discussion going.  Whenever I just post the answer, there is no discussion and the thread dies.


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## LCBob (Jul 30, 2019)

Maybe start at Table 8 of Chapter 9 and find that #3/0 wire is 167800 circular mils, times two is 335600 circular mils.
Now back to table 250.102(C)(1) and find that the supply side bonding jumper needs to be #2 copper or #1/0 aluminum.


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## jar546 (Jul 31, 2019)

LCBob said:


> Maybe start at Table 8 of Chapter 9 and find that #3/0 wire is 167800 circular mils, times two is 335600 circular mils.
> Now back to table 250.102(C)(1) and find that the supply side bonding jumper needs to be #2 copper or #1/0 aluminum.



Thank you for taking the time to correctly answer and explain how to do it.  This is what helps the forum to grow and become a great source of information.  You are correct.


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## LCBob (Aug 2, 2019)

Thank you, I enjoy the opportunity to add to the discussion.


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