# 3 Phase Question re same phase in conduit......



## conclavicus (Jul 25, 2016)

This is 4 parallel runs of 250 kcmil from A to B. Is it ok to run all the same conductors of a phase in same separate conduit. The four conduits are 3" PVC and about 4" apart.


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## Helmut (May 7, 2014)

conclavicus said:


> This is 4 parallel runs of 250 kcmil from A to B. Is it ok to run all the same conductors of a phase in same separate conduit. The four conduits are 3" PVC and about 4" apart.


I think it is commonly done to make it easier to terminate the wires inside switchgear. However, you still need to run a ground in each conduit.


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## Southeast Power (Jan 18, 2009)

conclavicus said:


> This is 4 parallel runs of 250 kcmil from A to B. Is it ok to run all the same conductors of a phase in same separate conduit. The four conduits are 3" PVC and about 4" apart.


I've seen that done with larger wire with a sawsall cut between the knockout entries. I can't say that I have ever considered doing it even with open bottom fed gear. 
I don't know why but, we just don't see that and when we do, it looks like someone screwed up real bad.

I don't know the application but, I would think smaller conductors would be flexible enough to bend anyway you needed them to.


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## Barjack (Mar 28, 2010)

I don't know if I'd do it, but it is legal.



> *300.3 Conductors.
> (B) Conductors of the Same Circuit.* All conductors of
> the same circuit and, where used, the grounded conductor
> and all equipment grounding conductors and bonding conductors
> ...


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## wildleg (Apr 12, 2009)

I would never do that, you are just asking for trouble with inductive heating at the entry points to the cabinets, so unless that is completely a non issue, then, as others have said, it's legal as long as the precautions are in place.


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## philipdybel (Feb 29, 2016)

*Compliant And Atypical*



Barjack said:


> > *300.3 Conductors.
> > (B) Conductors of the Same Circuit. ....
> > (1) Paralleled Installations. ....
> > *Exception: Conductors installed in nonmetallic raceways
> > ...


Concur with Bar. And as he quoted, 300.20(B) is how you minimize the inductive effect. Like Sun said, "a sawsall cut between the knockout entries" achieves that.

So it is NEC legal -- just a bit "atypical".

If it were my job, I'd print out a hard copy of these two code sections to show my boss, Client, and AHJ -- and probably discuss with him/them beforehand. "Just in case" they have the same question about this method (and they probably will).


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## ponyboy (Nov 18, 2012)

I've done it with 4 run parallel and 8 run parallel sets and I'll probably do it again anytime it lends itself as an option. The times we've done it have been some of the smoothest terminating projects I've ever experienced.


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## conclavicus (Jul 25, 2016)

Entering cabinet from bottom. I can cut rectangle around the four entry point knockouts such that no metal is closer that 2" from any of the 4 PVC conduits. This approach makes for very neat wiring with no crossing over of wires. 

One should NOT fear it since the code went to a lot of trouble to specifically allow it. The concern for inductive heating in this case is overstated IMHO.

Do I really need a bushing to terminate conduit entering bottom of cabinet. 300.16(B) seems to leave it optional and does not mandate it as I read it.


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## philipdybel (Feb 29, 2016)

*Trying To Clarify*

From how you describe it, you have a "cabinet" these conductors & raceways (PVC) go to.

(We know 300.10 states the general idea: "raceways ... shall be mechanically secured to boxes, fittings, cabinets, and other enclosures.")

300.16(B) lets you use a bushing only -- when your raceways terminate in "free air" such as the open bottom of a switchboard, or near "unenclosed control equipment or similar".

Does your "cabinet" sit directly on the ground or concrete? Based on what I've understood so far, I'm thinking no...

If not, if you've got "open air" between the ground and the bottom of your enclosure, 300.16(B) doesn't pertain...

In that case, again 300.20(B) gives you 2 options. The first is to punch 4 x 3" holes in the bottom, make a sawzall cut between the holes on their centerline, glue on your MA's and connect the PVC's to the cabinet. Mechanically secure, no open wires, no induction issue.

(The second option is an "insulating wall" on the bottom of the cabinet, which it doesn't have & you would have to fabricate onto the cabinet. Even after your time & expense doing this, some AHJ's will tell you to pay for an ETL to get a UL listing or equivalent on your as-modified cabinet.)

Unless I'm missing something here, the consensus is 300.20(B) Option (1)...


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## MechanicalDVR (Dec 29, 2007)

Just because you can doesn't mean you should.


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## ponyboy (Nov 18, 2012)

MechanicalDVR said:


> Just because you can doesn't mean you should.




Are you implying there's something wrong with using a method that is explicitly allowed by the nec? I can think of a lot of reasons why you would but almost none of why you shouldn't


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## philipdybel (Feb 29, 2016)

*What?*

Wait -- who is implying, what is wrong, and exactly which method?

I'm so confused...


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## ponyboy (Nov 18, 2012)

philipdybel said:


> Wait -- who is implying, what is wrong, and exactly which method?
> 
> I'm so confused...




I thought mechs statement in post 10 inferred that it wasn't a good idea to utilize the 300.3(B)(1) exception. But I wasn't sure


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## Brain John (Jul 15, 2016)

I have seen it done many times and when completed properly it works fine and simplifies tying in parallel feeders.

But when done improperly it leads to a real problem. I have posted IR pictures of excessive heating due to induction from this type of installation


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## philipdybel (Feb 29, 2016)

*What Do The Cameras Say?*

Hi Brain, you wrote:



Brain John said:


> I have seen it done many times and when completed properly it works fine and simplifies tying in parallel feeders.
> 
> But when done improperly it leads to a real problem. I have posted IR pictures of excessive heating due to induction from this type of installation


Regarding the aforementioned install we're discussing here -- the sawzall cut between the holes -- based on your experience, do you imagine this might be an inductive heating issue?

Even if it is NEC compliant, which it seems to be...

Please illuminate us non-IR_camera electricians & let us know what you've found, we want to prevent any such issues...


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## Brain John (Jul 15, 2016)

Philly, When slots are cut the issue of inductive heating was corrected same as when conductors were run in the top nipple of a side by side double panel and the neural through a nipple in the bottom of the panels, cut a slot and inductive heating issue resolved or use a non-ferrous plate for knockouts and take both conduits into the same plate.


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## philipdybel (Feb 29, 2016)

*Thank You*



Brain John said:


> When slots are cut the issue of inductive heating was corrected...


In other words: following 300.20(B)(1) here does not create an inductive heating problem.

Thanks Brain...


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## Big John (May 23, 2010)

Surprised to see some of you guys knocking this.

Yeah, it has the potential to cause problems if done wrong, but that's true of a lot of installs, no reason to write them off.

Done right this makes termination beautiful and about 1000% easier. I would do every large parallel run as segregated phases if I could.


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## conclavicus (Jul 25, 2016)

Big John said:


> Surprised to see some of you guys knocking this.
> 
> Yeah, it has the potential to cause problems if done wrong, but that's true of a lot of installs, no reason to write them off.
> 
> Done right this makes termination beautiful and about 1000% easier. I would do every large parallel run as segregated phases if I could.


This is the answer I was hoping to hear. In fact with this approach I would state that any possibility of wiring error is greatly reduced and inspection is greatly facilitated.


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## telsa (May 22, 2015)

Inspections are best facilitated with donuts and coffee.

Any seasoned hand knows* that.*


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## Southeast Power (Jan 18, 2009)

conclavicus said:


> This is 4 parallel runs of 250 kcmil from A to B. Is it ok to run all the same conductors of a phase in same separate conduit. The four conduits are 3" PVC and about 4" apart.


Im sure this is for your 1000amp service.
With small conductors like that, I would have them put up quadplexed on 4 separate reels. Also, I would size it for aluminum. Much more user friendly; especially for a small shop.


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## Tonedeaf (Nov 26, 2012)

I would run the phase A-B-C-N in one conduit per grouping. When A B C and N are ran together the magnetic fields around the conductors cancel each other out.

When they are separated they fields don't cancel and you get magnetic circuits with any Ferrous metals near by including the conduit they are ran in. This causes inductive heating.


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