downsizing the neutral in a parallel run

[tim89s]

I am installing an 800 amp panel. Calculated load is 750 amps. I plan on running two 3" conduits with 500 kcmil in each of them. Only 200 amps of the 800 amp panel will be using a neutral. The rest of the loads are stricly 3 phase. I was told by my project manager that you can take 125% of the 200 amps and size your neutral according to that. 1.25 x 200 = 250 amps. Since I am running parallel would I install 125 amp rated wire in each conduit? He didn't tell me what code section he got that from, I am interested to know. Any help would be great

Thanks Tim

 

[Dennis Alwon]

I don't know where he got it from either. Look at 250.24(C)(1)& (2)

 

[S'mise]

I bet he was confusing it with the 12.5% rule in 250.24C(1)

 

[don_resqcapt19]

is this the service or a feeder? It makes a difference what rules apply, but in this case the result would be the same....a 1/0 grounded conductor in each raceway.

 

[tim89s]

It is a feeder. Don can you please give me the code section that states I can run a 1/0 neutral. I believe 250.24c is talking about service entrance.

 

[tryinghard]

I think 250.24(C)(1) for service and 250.30(A)(3)(b) from XFMR feeder & such.

But notice 310.10(H), basically even though there?s only 200A neutral load this parallel has to be at least 1/0

 

[Dennis Alwon]

The grounded conductor of a feeder can be as small as the EGC but no smaller. For the service no smaller than the GEC unless the service conductors are over 1100 kcm

 

[don_resqcapt19]

The code rules that would apply to a feeder grounded conductor are 220.61 and 215.2(A)(2). You need to use the larger of the two. Also the rules for parallel conductors apply.

 

[Dennis Alwon]

The code rules that would apply to a feeder grounded conductor are 220.61 and 215.2(A)(2). You need to use the larger of the two. Also the rules for parallel conductors apply.

Thanks Don I forgot to state the code article.

 

[tim89s]

Thank you all very much for info
Tim