wire derating

[patl]

I am feeding a bank of meters with a 3ph 120/208 Y system source, the meters are 1ph 120/208, the AHJ is telling me I must derate the wires feeding the meter banks because there are 4 wires in the conduit he says the neutral must be counted as a current carrying conductor. Is this right?

 

[steve66]

Re: wire derating

The neutral is not counted as a current carrying conductor when it only carries the unbalance of the other conductros of the same circuit (unless the loads are mostly nonlinear.) 310.15(2)(B)(4)(a).

 

[don_resqcapt19]

Re: wire derating

If you are using two hots and the grounded conductor from a 208/120 wye system the grounded conductor is a current carrying conductor.
Don

 

[physis]

Re: wire derating

It's an interesting question. I don't do a lot of services so I'm curious too. Are they entrance conductors or feeders?

I'm looking at 310.1 Scope. and wondering if derating does or doesn't apply.

 

[pierre]

Re: wire derating

Sam
What would be the difference?

 

[physis]

Re: wire derating

I don't really know, that's why I'm curious too now.

I've never heard of derating service conductors.

Edit: I haven't found a code difference if that's what you mean.

[ April 29, 2005, 06:54 PM: Message edited by: physis ]

 

[pierre]

Re: wire derating

I think that most installers will rarely install a service entrance with more than 3 current carrying conductors in a raceway. Maybe that is why.

 

[iwire]

Re: wire derating

Derating certainly applies to service entrance conductors.

90.3 Code Arrangement.
This Code is divided into the introduction and nine chapters, as shown in Figure 90.3. Chapters 1, 2, 3, and 4 apply generally;

I have seen a number of times on this forum that people have talked about using two sets of 3/0 or 4/0 in a single raceway for a service.

That would be subject to an 80% derating.

 

[charlie]

Re: wire derating

I am feeding a bank of meters with a 3ph 120/208 Y system source

He has only 3 current carrying conductors. He is feeding a meter center and from there he is feeding two phases and the grounded conductor to each apartment. It is residential load so harmonics will not be a problem.