T250.102

[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

 

[packersparky]

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.

 

[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.

 

[infinity]

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

 

[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

 

[kwired]

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.

 

[tshea]

Thanks!

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!