Question on a parallel conductors feeder

[mshields]

I have a single existing 4 inch conduit that I'd like to use for a 500A feeder (I want to avoid adding a parallel conduit). It appears to me that I can do this with 2 sets of 400kcmil compact copper conductors.

Given that I'll have 8 current carrying conductors, I'll derate to 70% which gives me a total ampacity (2 conductors) of 468A which allows me to use a 500A breaker.

Couple of questions:

1. I wouldn't ordinarily provide parallel conductors in the same conduit. Other than having to worry about derating, is there any code rule not permitting it.

2. I know they make compact Aluminum. Do they in fact make compact Copper? Is it readily available? If so, who makes it?

Thanks,

Mike

 

[ericsherman37]

1. I wouldn't ordinarily provide parallel conductors in the same conduit. Other than having to worry about derating, is there any code rule not permitting it.

I don't know what kind of conductors or conduit it is, but you might make sure your conduit fill will be compliant. If it's Schedule 40 PVC and 400 kcmil XHHW, for instance, you'd be maxed out at 8 conductors total.

2. I know they make compact Aluminum. Do they in fact make compact Copper? Is it readily available? If so, who makes it?

Not a clue. Google it?

 

[iwire]

I have a single existing 4 inch conduit that I'd like to use for a 500A feeder (I want to avoid adding a parallel conduit). It appears to me that I can do this with 2 sets of 400kcmil compact copper conductors.

Given that I'll have 8 current carrying conductors, I'll derate to 70% which gives me a total ampacity (2 conductors) of 468A which allows me to use a 500A breaker.

Yes but I bet you really only have 6 current carrying condutors which would bring your derating to 80% not 70%.

Couple of questions:

1. I wouldn't ordinarily provide parallel conductors in the same conduit. Other than having to worry about derating, is there any code rule not permitting it.

No, you can do that.

2. I know they make compact Aluminum. Do they in fact make compact Copper? Is it readily available? If so, who makes it?

I have never heard of compact copper.

 

[infinity]

Yes but I bet you really only have 6 current carrying condutors which would bring your derating to 80% not 70%.

That would be my assumption too.

 

[don_resqcapt19]

I know that compact copper conductors are available in 5kV cable, but not sure about 600 volt cable.

 

[jwjrw]

Yes but I bet you really only have 6 current carrying condutors which would bring your derating to 80% not 70%.

Is that because you are assuming he does not have a 4 wire 3 phase feeder supplying mainly non- linear loads or am I clueless again?

 

[infinity]

Is that because you are assuming he does not have a 4 wire 3 phase feeder supplying mainly non- linear loads or am I clueless again?

Yes, unless there is a rare loading condition a feeder will never have a non-linear load of more than 50%. Therefore the neutrals would not be considered a CCC for derating purposes.

 

[jwjrw]

Yes, unless there is a rare loading condition a feeder will never have a non-linear load of more than 50%. Therefore the neutrals would not be considered a CCC for derating purposes.

That was the first thing that popped in my head when I read Bobs post. Thanks!

 

[mshields]

6 CCC's

6 CCC's

That's huge (in terms of information). That will make the difference. Thanks,

Mike

 

[mshields]

where current carrying conductor is defined

where current carrying conductor is defined

Where in the NEC does it say that a conductor has to carry more than 50% of the rated load in order to be considered a current carrying conductor?

Thanks,

Mike

 

[don_resqcapt19]

Take a look at 310.15(B)(4)(c).

 

[kevin]

It is not required that you install install parallel neutral conductors if you have only one raceway. Assuming that you don't have more than 50% nonlinear loads, a load calculation for the neutral will probably result in a very small conductor size. None of that load will be required to be increased by 25% [215.2(A)(1)Ex No. 2]; but the minimum size of the neutral will be 2AWG Cu or 1/0 AWG Alum [215.2(A)(1) and 250.122].