Parallel conductors

[101010]

Can you parallel two sets of 350's in one 4" and still put under a 600 amp breaker? 120/ 208
v wye. That would be 560 amps after derating right?

 

[shamsdebout]

I would say yes you can per 240.4(B), but how did you get your derated ampacity though?

 

[101010]

350x350x80%=560 I should also say this is from the secondary of a transformer

 

[chris kennedy]

I should also say this is from the secondary of a transformer

Did you look at 240.21(C)?

 

[infinity]

You'll need a minimum of 600 amps worth of conductors not less. As Chris posted read the last sentence in that section.

 

[101010]

So this would have to be in two seperate pipes Right? How about a trough?

 

[infinity]

You have several options, one conduit and larger conductors or two conduits with the 350's or one wireway with the 350's.

 

[101010]

I am looking at 240.21c . My secondaries might be less the 10 ft long . If they are not is this ok?

 

[101010]

If I do a wireway(trough) does that change when I change over to greenfield to enter the transformer?

 

[don_resqcapt19]

I am looking at 240.21c . My secondaries might be less the 10 ft long . If they are not is this ok?

Still not ok...the conductors must have an ampacity equal to or greater than the rating of the OCPD. 240.4(B) does not apply to these conductors.

(C) Transformer Secondary Conductors. A set of conductors feeding a single load, or each set of conductors feeding separate loads, shall be permitted to be connected to a transformer secondary, without overcurrent protection at the secondary, as specified in 240.21(C)(1) through (C)(6). The provisions of 240.4(B) shall not be permitted for transformer secondary conductors.

 

[Pierre C Belarge]

Still not ok...the conductors must have an ampacity equal to or greater than the rating of the OCPD. 240.4(B) does not apply to these conductors.

Don
Why would 2 sets of 350 kcmil not work for this installation to a 600A overcurrent device?

 

[eprice]

Don
Why would 2 sets of 350 kcmil not work for this installation to a 600A overcurrent device?

Not to answer for Don, but the OP is asking about putting those two sets in one conduit. With the derating required for 6 current carrying conductors, two sets of 350s have an ampacity of 560 amps. The OP also states that these are the secondary of a transformer. As pointed out, 240.21(C) does not allow the use of 240.4(B) to round up to the next OCP rating.

 

[augie47]

If I do a wireway(trough) does that change when I change over to greenfield to enter the transformer?

Only if your raceway for the paralleled conductors is less than 24".
Since, as Charlie noted, you have to have full ampacity rating for transformer secondary conductors, if you do anything that derates your conductors beyond 14% you would be in violation.
(Assuming 350 THHN 300/350 =.86 =301 amps)