Thread: T250.102

1. T250.102

480/277 volt service
parallel 3 * 750mcm AL XHHW-2
per table 3*750= 2250mcm * 12.5% = 281.xx mcm

Main Bonding jumper needs to be 300mcm

POCO inspector said 4/0

What am I missing here?

Thanks for all the help.

tim

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I have never heard of a POCO inspector around here. I don't think you are missing anything. You need a 300 kcmil for your main bonding jumper.

3. I wonder if the power company guy is using the grounding electrode conductor table which is 250.66. T 250.102 was added more recently and the only change is at the bottom of the table 250.102 otherwise the two tables are identical.

4. Maybe he saying #4/0 copper. I didn't do the calculation so I'm guessing.

5. Originally Posted by Dennis Alwon
I wonder if the power company guy is using the grounding electrode conductor table which is 250.66. T 250.102 was added more recently and the only change is at the bottom of the table 250.102 otherwise the two tables are identical.

Forget this-- this table only goes to 3/0-- I misread the question.... Anyway I believe you are correct but what difference does it make. You will more than satisfy the power company with 300 kcm anyway.

Trevor does have a point about copper vs aluminum

6. Originally Posted by tshea
480/277 volt service
parallel 3 * 750mcm AL XHHW-2
per table 3*750= 2250mcm * 12.5% = 281.xx mcm

Main Bonding jumper needs to be 300mcm

POCO inspector said 4/0

What am I missing here?

Thanks for all the help.

tim
If 4/0 is all that is needed and you ran 300 - I don't see a problem, run 750 if you want.

7. Thanks!

I have some scrap 4/0 and 300mcm. Think I'll take both pieces with and whichever fits the lugs...

I'll use the 300mcm. Don't want to have the guy call me again.

Thanks again!

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