Sizing Conductors

[horses]

I have a meterbank on the back of a new retail space. It has a 1600A 3P main disconnect. Normally the power company supplies/install the secondary conductors from the transformer. In this case the power company has required us to supply them. The engineer on the job said that he wanted (4) parallel runs of 500mcm copper. According to article 240-3b the conductors need to be rated equal to or greater than the 1600A overcurrent device. With that being said I believe there should be (4) parallel runs of (4) 600mcm copper conductors to satisfy the code. Your opinion on this matter would be greatly appreciated.

Thanks

 

[charlie b]

I agree with you. It is possible to use four sets of 500s, but only if (1) The calculated load is under 1,520 amps, and (2) You set the overcurrent device to trip at 1,520 amps. I don't think it likely that you will be able to prove #1, which puts you back to four sets of 600s.

 

[kingpb]

Check the main device and ascertain if it can be set to a lower value, if not, send the engineer an RFI that says: "The 1600A protective device does not have the capability to set it at 1520A, which would be required for the 4 x 500Kcmil conductors per phase that are specified."

Proposed resolution, " Should I change the main to an adjustable breaker capable of setting it at 1520A, or should I increase the cable size?"

When you get your answer, then send in your change order! Make it reasonable, but don't forget your legitimate 25% mark-up for overhead and profit.:grin:

 

[infinity]

If you don't want to wrestle with 600's you could use (5) sets of 400's.

 

[horses]

Thanks for the input!

 

[petersonra]

it might be more profitable to install what the engineer asked for and than fix it later.

 

[winnie]

Is it possible that even though these conductors are being supplied by the customer/EC, that they are still to be sized under POCO rules rather than the NEC?

-Jon

 

[charlie b]

Yes that is possible. Perhaps Don can offer a few thoughts?

 

[don_resqcapt19]

Charlie,
It appears that these conductors are on the line side of the sevice point and under the exclusive control of the utility and as such are outside of the scope of the NEC. In my opinion, just the fact that the EC is providing and installing them does not change anything.
Don