parallel conductors in the same conduit

[mshields]

I was recently asked by a contractor if they could run parallel 4/0 instead of a single set of 500kcmil (for a 400A feeder). And he wants to put them all in the same pipe.

Assuming we can do that within the limitations of the 40% rule, how many ground conductors are required. Do you just need the one in accordance with 250.122.


Also, as we will have a neutral, do I have to derate for 8 current carrying conductors?


Thanks,

Mike

 

[Dennis Alwon]

One equipment grounding conductor and assuming 3 phase the neutrals probably don't count for de-rating. I assume the loads isn't mainly lighting

310.15(B)(5) Neutral Conductor.
(a) A neutral conductor that carries only the unbalanced
current from other conductors of the same circuit shall not be
required to be counted when applying the provisions of
310.15(B)(3)(a).

(b) In a 3-wire circuit consisting of two phase conductors
and the neutral conductor of a 4-wire, 3-phase, wye-connected
system, a common conductor carries approximately the same
current as the line-to-neutral load currents of the other
conductors and shall be counted when applying the provisions
of 310.15(B)(3)(a).

(c) On a 4-wire, 3-phase wye circuit where the major
portion of the load consists of nonlinear loads, harmonic
currents are present in the neutral conductor; the neutral
conductor shall therefore be considered a current-carrying
conductor

 

[petersonra]

I was recently asked by a contractor if they could run parallel 4/0 instead of a single set of 500kcmil (for a 400A feeder). And he wants to put them all in the same pipe.

Assuming we can do that within the limitations of the 40% rule, how many ground conductors are required. Do you just need the one in accordance with 250.122.


Also, as we will have a neutral, do I have to derate for 8 current carrying conductors?


Thanks,

Mike

ground conductors are selected according to the size of the OCPD protecting the circuit conductors. so yes, 250.122 is the appropriate criteria.

having said that, if you have upsized the conductors from the bare minimum required you have to upsize the EGC by a proportional amount. 4/0 isd about 212 kcm so (2) 4/0 is less than 500 kcm so no upsizing is needed.

if the neutral is considered a CCC, then you have to derate accordingly. see 310.15 (B) (5). It might not be considered a CCC.

 

[kingpb]

I was recently asked by a contractor if they could run parallel 4/0 instead of a single set of 500kcmil (for a 400A feeder). And he wants to put them all in the same pipe.

Assuming we can do that within the limitations of the 40% rule, how many ground conductors are required. Do you just need the one in accordance with 250.122.


Also, as we will have a neutral, do I have to derate for 8 current carrying conductors?


Thanks,

Mike

Out of curiosity, why does he want to do that?

 

[petersonra]

Out of curiosity, why does he want to do that?

perhaps because (2) 4/0 conductors are less copper than a single 500 kcm conductor and thus might be cheaper.

or maybe he just has 4/0 laying around he wants to use.

or maybe he already did it in 4/0 for some reason.

is it metal conduit? if so skip the EGC wire altogether.

 

[mshields]

Thank you gentlemen

Thank you gentlemen

As to why! As it turns out, he's just running through a couple of nipples from main to ATS to panel. He said the 4/0 will be easier to terminate.

 

[petersonra]

As to why! As it turns out, he's just running through a couple of nipples from main to ATS to panel. He said the 4/0 will be easier to terminate.

as good a reason as any. however, nipples are not conduit and IIRC, the so called derating for number of CCC is not required anyway.

 

[infinity]

As to why! As it turns out, he's just running through a couple of nipples from main to ATS to panel. He said the 4/0 will be easier to terminate.

If they're 24" or less there is no derating required and the fill goes up to 60% so a smaller raceway may be used.

 

[kingpb]

As to why! As it turns out, he's just running through a couple of nipples from main to ATS to panel. He said the 4/0 will be easier to terminate.

The no hassle for engineer answer is then I would say have him install it as designed.

The be the nice guy answer is; "sure, just don't ask for a CO".

 

[JoeStillman]

310.15(B)(3) Says that table 310.15(B)(3)(a) (over 3 conductors) derating does not apply for raceways under 24"

 

[petersonra]

310.15(B)(3) Says that table 310.15(B)(3)(a) (over 3 conductors) derating does not apply for raceways under 24"

several posters have already pointed that out.

 

[Coppersmith]

perhaps because (2) 4/0 conductors are less copper than a single 500 kcm conductor and thus might be cheaper.

or maybe he just has 4/0 laying around he wants to use.

or maybe he already did it in 4/0 for some reason.

is it metal conduit? if so skip the EGC wire altogether.

You forgot to mention 4/0 is way easier to bend than 500's.