Parallel run for small wires

C

Charlypt

Senior Member
Location
Florida
Occupation
Electrician
We need to feed an existing subpanel and increase its capacity from 60 to 100A. The feed comes through a 3/4" conduit, and there are spare conduits.

The code prohibits running parallel cables smaller than 1/0". I'm not entirely convinced by the reasons, but that's the rule.
We're trying to find a solution before running new conduits and wires.

There could be another solution if we find a third conduit coming out of the same panel based on 300.3(B)(1):
Exception: Conductors installed in nonmetallic raceways run underground shall be permitted to be arranged as isolated phase, neutral, and ground conductor installations. The raceway shall be installed in close proximity, and the isolated phase, neutral, and grounded conductor shall comply with 300.20(B).

I understand this means we can run:
  • phase A, in one conduit. Wire #3 AWG.
  • phase B, in another conduit. Wire #3 AWG.
  • Neutral and ground in the 3rd separated conduit, maybe.

Has anyone done something like this, and is there anything that would prevent me from doing it? I've seen installations like this for large service wires, but never for small ones.
 
curt swartz said:
Your proposed installation is not considered parallel conductors. You need to comply with 300.3(B).
Click to expand...
It's an exception. If not, explain your interpretation.
Check this out:

300.3(B) exception and 300.20(B)

It has always been my understanding of these two sections that, when running feeders in seprate conduits per phase (One conduit for A phase, one for B, etc.) that ANY ferrous metal in the system, including a simple locknut, negated the exception making it mandatory to put A-B-C-N in each...
forums.mikeholt.com
 
My question would be, if only increasing from 60 to 100, what are you adding to the Sub Panel that it wont already handle?

Jap>
 
The proposed installation is not parallel conductors. In order to run the phase and neutral conductors in separate conduits they would need to be in PVC. Typically this is done into open bottom switchboards.
 
infinity said:
The proposed installation is not parallel conductors. In order to run the phase and neutral conductors in separate conduits they would need to be in PVC. Typically this is done into open bottom switchboards.
Click to expand...
Nasty little thing called ferrous? heating.....
 
Charlypt said:
It's an exception. If not, explain your interpretation.
Check this out:

300.3(B) exception and 300.20(B)

It has always been my understanding of these two sections that, when running feeders in seprate conduits per phase (One conduit for A phase, one for B, etc.) that ANY ferrous metal in the system, including a simple locknut, negated the exception making it mandatory to put A-B-C-N in each...
forums.mikeholt.com
Click to expand...
Its an exception if you are installing parallel conductors which you are NOT.
 
infinity said:
The proposed installation is not parallel conductors. In order to run the phase and neutral conductors in separate conduits they would need to be in PVC. Typically this is done into open bottom switchboards.
Click to expand...
The underground pipes and fittings are PVC. You can use non-metallic or non-ferrous lock-nuts maybe.
 
If the conduit is all non-ferrous, and any entry to a ferrous enclosure is through a common non-ferrous window, what is proposed is allowed under 300.3(B)(3).

300.3(B)(1) is not relevant, as the proposed installation does not have any parallel conductors. 300.3(B)(1) Exception is redundant to 300.3(B)(3).

Cheers, Wayne
 
wwhitney said:
If the conduit is all non-ferrous, and any entry to a ferrous enclosure is through a common non-ferrous window, what is proposed is allowed under 300.3(B)(3).

300.3(B)(1) is not relevant, as the proposed installation does not have any parallel conductors. 300.3(B)(1) Exception is redundant to 300.3(B)(3).

Cheers, Wayne
Click to expand...
Okay, I think I understand now. There have to be several conductors of the same phase in each pipe, and one pipe per phase.
 
wwhitney said:
Yes, for 300.3(B)(1) Exception. But you can use 300.3(B)(3) for what you propose.

Cheers, Wayne
Click to expand...
They would still need to comply with the non-ferrous entry into the enclosures on each side.

With larger commercial panels this can be accomplished with notches or cutting out a section of the end wall and replacing it with a non ferrous section.

With residential grade load centers it not as easy to modify them.

You could install a underground hand hole (AKA Christy Box) or a surface mounted PVC box on the wall and bring a single raceway into the panel.
 
This sounds like both ungrounded conductors of single phase, wouldnt have considered this simply on the basis I want the ground wire and the N wire running with the ungrounded in same pipe cable or raceway. Sounds like,,, well we simply want to avoid running a new pipe which might be the easy way. Sometimes digging a ditch is easier too.
 
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