Parallel feeds which are grouped together by phases

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riverjig87

riverjig87

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Minot, North Dakota, USA
I have searched this forum for a clear answer. I believe the inspector to be mistaken by NEC 300.20. and 300.20 (b)

We have (3) 4" chase nipples installed from a ferrous gutterway attached to a feeder section. Each set of phases is being ran through each chase. Example, 3- A phase conductors, 3- B phase conductors, and 3- C phase conductors through each chase nipple into the enclosure. There is no grounded conductor.

According to my understanding, this would violate 300.20 and cause induction due to the ferrous metal enclosure. The inspector seems think that it is not a violation since its only a chase nipple and its a short distance. I would love some clarification.

Everything I have seen through my search indicates nipples (which I understand these are) and PVC conduit. There is no clear cut answer.

Thanks for your help
 
Even ferrous lock nuts or the ferrous enclosure wall can cause excessive heating if the installation is an "isolated phase" installation.
 
This is the situation in question:

156tzbo.jpg


They are being fed from a CT can outside of an MCC. These are the feeders to the MCC main disconnect. Here is the CT can:



5x64g2.jpg
 
I agree. That's what I'm trying to point out. I think the justification is its "just" a chase nipple, according to the inspector

And its not following the NEC for rules on parallel conductors either.

Thanks for the help.
 
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riverjig87 said:
I did sir. 300.20 (B) spells it out pretty clear. The question was the short distance/penetration.
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I don't see where there is any exception in regard to distance.

riverjig87 said:
Wow. You are 100% right......
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I thought that also but it looked like some type of cable as opposed to individual conductors in which case it would be acceptable.
 
riverjig87 said:
I did sir. 300.20 (B) spells it out pretty clear. The question was the short distance/penetration.
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The nipple is much longer than the enclosure wall is thick...the rule says you have to cut slots in the enclosure wall if it is ferrous and you install the conductors like that, so it stands to reason that the nipples are not permitted. You could use aluminum nipples and lock nuts and cut slots between the holes and comply with the rule.
 
augie47 said:
I don't see where there is any exception in regard to distance.





I thought that also but it looked like some type of cable as opposed to individual conductors in which case it would be acceptable.
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There isn't. The original argument (if it can even be called that) was that I brought up that this installation violated NEC 300.20. It was told to me that the AHJ has already approved this installation because of it "only being chase nipples". I made the argument that whether or not it was chase nipples or 10" nipples, it was still a violation. The reason for the OP,in retrospect, was validation of my interpretation of a very clear code.





The wires on the bottom of that can are cable assemblies. However, the cables on the top are individual conductors. Re-identification of the gray wire to use as ungrounded violates 200.7 (C).
 
don_resqcapt19 said:
The nipple is much longer than the enclosure wall is thick...the rule says you have to cut slots in the enclosure wall if it is ferrous and you install the conductors like that, so it stands to reason that the nipples are not permitted. You could use aluminum nipples and lock nuts and cut slots between the holes and comply with the rule.
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At this point, its going to be easier to re-route the cables. Cutting a slot is going to be difficult.
 
riverjig87 said:
This is the situation in question:

156tzbo.jpg


They are being fed from a CT can outside of an MCC. These are the feeders to the MCC main disconnect. Here is the CT can:



5x64g2.jpg
Click to expand...
Top picture: the nipples provide equipment grounding between enclosures. If these are service conductors there needs to be a grounded conductor and bonding to the nipples though. But if I understand correctly this is a feeder circuit. Each raceway (even if just a short nipple) needs to have one conductor of each phase plus grounded conductor (if one is needed) to eliminate inductive effects on the raceway.

You could cut slots between each hole and use non metallic nipples - without steel locknuts- and then you effectively have a single hole in the ferrous material in which all conductors pass through - you then need a bonding jumper between enclosures to ensure continuity of the equipment grounding though.


bottom picture, I think you need to place all conductors in same raceway or add a third raceway with one "set" in each raceway. Though it is non metallic raceway and the consequences are in reality pretty minimal - that is not what is allowed by the wording of the code.

Also there doesn't appear to be an equipment grounding conductor between the enclosures on each end of those PVC raceways. If it is service conductors then an EGC is not needed but the grounded service conductor is needed and would need to be bonded to each metallic enclosure.

Assuming the white conductors marked with yellow tape at the bottom are part of some cable assembly and would be permitted to be re-identified?

I have more concerns with the bonding then with the issues with parallel conductors, if this is the feeder to the building - there appears to not be a link to the equipment grounding conductor to the rest of the building that is run with the feeder.
 
kwired said:
Top picture: the nipples provide equipment grounding between enclosures. If these are service conductors there needs to be a grounded conductor and bonding to the nipples though. But if I understand correctly this is a feeder circuit. Each raceway (even if just a short nipple) needs to have one conductor of each phase plus grounded conductor (if one is needed) to eliminate inductive effects on the raceway.
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Gotta be careful that you use zinc/Al/stainless bonding bushings, and aluminum or stainless conduit, if doing an isophase installation.

Anything iron will have magnetization issues, including malleable iron bonding bushings, steel locknuts, and steel raceways. Is the steel enclosure still an issue?

Stainless has iron, but has other alloy components that cancel out most of its magnetism.
 
Carultch said:
Gotta be careful that you use zinc/Al/stainless bonding bushings, and aluminum or stainless conduit, if doing an isophase installation.
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Careful of what? Letting the inspector see it? :D

The following is the exception to 300.3(B)(1) that allows paralleled isolated phase installations.


Exception: Conductors installed in nonmetallic raceways
run underground shall be permitted to be arranged as isolated
phase installations. The raceways shall be installed in
close proximity, and the conductors shall comply with the
provisions of 300.20(B).
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iwire said:
Careful of what? Letting the inspector see it? :D

The following is the exception to 300.3(B)(1) that allows paralleled isolated phase installations.
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Even when using PVC, the steel locknut that is common to use with PVC, would have magnitization issues. So one would need to make sure to use plastic locknuts. I wasn't sure if it was non-ferrous, or non-metallic that matters.

The way I see the rules on isolated phase, it seems like it is a better practice just to avoid it all together.

Another example I've seen, is the DC equivalent of isophase. Isolated polarity installations. There is no magnetic heating that would occur, only a steady magnetic field in the conduit. I remember specifying a 1 1/4" conduit to take 6 DC conductors. It ended up getting built with two 1" conduits, and the positives in one, with negatives in the other.
 
Carultch said:
Even when using PVC, the steel locknut that is common to use with PVC, would have magnitization issues.
Click to expand...

I have personally installed three isolated phase services and have never used a lock nut or a metal bushing.

The rules of 300.20(B) would make you put a slot in those items unless they were non-ferrous

The way I see the rules on isolated phase, it seems like it is a better practice just to avoid it all together.
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There are some hoops to jump through but it has its uses.


Another example I've seen, is the DC equivalent of isophase. Isolated polarity installations. There is no magnetic heating that would occur, only a steady magnetic field in the conduit. I remember specifying a 1 1/4" conduit to take 6 DC conductors. It ended up getting built with two 1" conduits, and the positives in one, with negatives in the other.
Click to expand...


Unless it is in 690 I do not know of exception for DC, you would still be stuck complying with 300.3 and 300.20(B). (I understand DC does not cause he magnetic heating, I am just saying the NEC does not seem to account for that)

This picture was not one I worked on but one a coworker of mine had asked me about. I posted it on the net a few years ago so it is everywhere now.

This is pretty typical of the ones I have worked on and the advantage is that you do not have to chris cross all the conductors. A downside is now you have four CCCs in each raceway subject to derating.

Als_Isolated_Phase.JPG
 
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