# Service conductor sizing



## Adam12 (May 28, 2008)

We have an 800 amp main switch gear on our job. I was looking at the single line diagram and feeder schedule. I looked up the note regarding the service conductors and all it said was the POCO's name.

I noticed table 310-16 only covers up to 430 amps. 

Is 800 amps out of reach for the NEC?

I am asking because I was trying to size the cold water bond to compare to the plans.


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## Dennis Alwon (May 9, 2009)

Adam you would have to base the water pipe bond on the size of the service conductors. Thus for 800 amps you probably have a parallel set of either copper or aluminum conductors.

You would have to add the cir mil of the conductors. Thus if you had a pair of 600 kcm conductors you would double it and get 1200 cir mil. If you had parallel 500kcm you would use 1000 cir mil. Then go to T. 250.66


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## Dennis Alwon (May 9, 2009)

You would be safe to run a 3/0 copper conductor since you never need a bond bigger than that.


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## william1978 (Sep 21, 2008)

I agree with the 3/0.


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## Adam12 (May 28, 2008)

Dennis Alwon said:


> Adam you would have to base the water pipe bond on the size of the service conductors. Thus for 800 amps you probably have a parallel set of either copper or aluminum conductors.
> 
> You would have to add the cir mil of the conductors. Thus if you had a pair of 600 kcm conductors you would double it and get 1200 cir mil. If you had parallel 500kcm you would use 1000 cir mil. Then go to T. 250.66


Thanks Dennis. I understand how to size the CW bond I just wanted to compare my calculation to the Engineer's and yes they are in parallel.



Dennis Alwon said:


> You would be safe to run a 3/0 copper conductor since you never need a bond bigger than that.


The plan calls for a 3/0. 

I didn't know that, why is that?


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## Dennis Alwon (May 9, 2009)

Adam12 said:


> Thanks Dennis.


 You're welcome



> The plan calls for a 3/0.
> I didn't know that, why is that?


I don't know why you never need more than 3/0. I guess they figure that is plenty big to bond anything thst needs bonding. Sorta like why we only need a #6 to a ground rod-- the rod is only as functional as a #6 copper conductor.


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## Adam12 (May 28, 2008)

Dennis Alwon said:


> You're welcome
> 
> 
> 
> I don't know why you never need more than 3/0. I guess they figure that is plenty big to bond anything thst needs bonding. Sorta like why we only need a #6 to a ground rod-- the rod is only as functional as a #6 copper conductor.


 
And you never need more than a #4 to a UFER.

250.66 bottoms out @ a 3/0

Thanks again :thumbsup:


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