Parallel sets, Conductor bundling, and the 24 inch & less exception

[Carultch]

I understand that parallel feeder sets have to be routed under conditions that would give each set an identical resistance. Same length, same conditions of use, same conduit, same terminations, etc. 310.10(H).

I have a situation where I have two parallel 4" conduits to work with, and I have to tap 800A of wire onto a 3-set single phase 1200A feeder. They penetrate a substantial wall, which I'd rather not add in another penetration.

One potential solution is to use 3 sets of 300 kcmil, and send two sets in one of the conduits, with the remaining set in the third. Like I said, conduits are less than 24", so the following would ordinarily apply in any other situation: 310.15(B)(2)(a) Exception No. 3: Derating factors shall not apply to conductors in nipples having a length not exceeding 600 mm (24 in.)

Sets 1 and 2 in the first conduit still have the same ampacity adjustment factor due to bundling as set 3 in the second conduit. I.e. no ampacity adjustment, due to the length. But it doesn't exactly "feel right".

Other solutions:
1. Isolated "phase" installation. Black phase in pipe 1, red phase in pipe 2. Distribute the non-current-carrying neutral however it may fit, and a ground in each. It is PVC conduit.
1. 8-terminal tap connectors, for 3 wires in / 3 wires out / 2 wires tapped.

 

[iwire]

I
One potential solution is to use 3 sets of 300 kcmil, and send two sets in one of the conduits, with the remaining set in the third. Like I said, conduits are less than 24", so the following would ordinarily apply in any other situation: 310.15(B)(2)(a) Exception No. 3: Derating factors shall not apply to conductors in nipples having a length not exceeding 600 mm (24 in.)

Sets 1 and 2 in the first conduit still have the same ampacity adjustment factor due to bundling as set 3 in the second conduit. I.e. no ampacity adjustment, due to the length. But it doesn't exactly "feel right".

That is not right and a violation of the rules for parallel conductors. 24" and derating don't enter into it.

Other solutions:
1. Isolated "phase" installation. Black phase in pipe 1, red phase in pipe

Unless it is underground that is a violation.

2. Distribute the non-current-carrying neutral however it may fit, and a ground in each. It is PVC conduit.

[/QUOTE]

I don't get this one but 300.3(B) will likely be an issue.

8-terminal tap connectors, for 3 wires in / 3 wires out / 2 wires tapped.

Bingo, IMO this is one of the few ways you can do this and it is how a I made a 400 and 800 amp tap from a 1,200 amp feeder.

 

[Smart $]

I agree with Bob (iwire) on 2 sets in one, 1 set in the other conduit. [310.10(H)(3).

I don't agree with Bob that isophase is limited to underground... but only if you comply with both 300.3(B)(1) & (3)... which amounts to complying with 310.10(H)(3), using a non-metallic wiring method and complying with 300.20(B)... but you will not be able to comply if you have three sets of 3 conductors each.

What I see as the best way is to run either 2 or 4 sets divided between the 2 conduits. If the 1200A wire is 3 sets, 2 sets of the same size (600kcmil...?) should be capable of 800A, but you can use 4 sets (250kcmil...?) to reduce the wire size [not sure where you are getting this 310.15(B)(2)(a) Exception No. 3, but 310.15(A)(2) Exception may apply].

 

[Carultch]

but you will not be able to comply if you have three sets of 3 conductors each.

Well, I'd have 3 sets of A-phase conductors, and 3 sets of B-phase conductors. No C-phase because it is a single phase system.

The neutral I suppose needs its own conduit for isolated phase installations in single phase systems. Can't distribute a no-current neutral among the other two. I try to avoid isolated phase whenever possible.

What I see as the best way is to run either 2 or 4 sets divided between the 2 conduits. If the 1200A wire is 3 sets, 2 sets of the same size (600kcmil...?) should be capable of 800A, but you can use 4 sets (250kcmil...?) to reduce the wire size

It's only a few feet anyway. It's going through a 2 ft conduit, and the rest is just bending room within the equipment.

It would need to be 2 sets of 600, 4 sets of 4/0, or 6 sets of 1/0. An even number of sets, as we've discussed. Makes perfect sense.

Too many sets complicates the tap connector size.

not sure where you are getting this 310.15(B)(2)(a) Exception No. 3, but 310.15(A)(2) Exception may apply].

I don't have a code book, so maybe I looked it up wrong. I was trying to find the 2 foot nipple rule.

 

[Smart $]

Well, I'd have 3 sets of A-phase conductors, and 3 sets of B-phase conductors. No C-phase because it is a single phase system.

The neutral I suppose needs its own conduit for isolated phase installations in single phase systems. Can't distribute a no-current neutral among the other two. I try to avoid isolated phase whenever possible.

As I said, 3 sets of 3 conductors will not apportion equally in 2 conduits.

I don't have a code book, so maybe I looked it up wrong. I was trying to find the 2 foot nipple rule.

310.15(B)(3)(a)(2)

3/0 will work for 4 sets if you don't have to correct for high ambient.

 

[iwire]

I don't agree with Bob that isophase is limited to underground...

Sure would be glad to hear why

 

[GoldDigger]

Sure would be glad to hear why

Not relevant to the OP's problem, but MI cable comes to mind.

 

[don_resqcapt19]

Sure would be glad to hear why

The wording in 300.3(B)(3) clearly permits isolated phase installations in any location. I don't see any need for the exception to 300.3(B)(1) to exist, and I don't see how that specific permission to use an isolated phase installation underground would act to prohibit what is permitted by 300.3(B)(3).
Note that the CMP does not agree with me, but I don't see how you can apply the words any other way.

 

[Smart $]

Sure would be glad to hear why

Already answered...

The wording in 300.3(B)(3) clearly permits isolated phase installations in any location. I don't see any need for the exception to 300.3(B)(1) to exist, and I don't see how that specific permission to use an isolated phase installation underground would act to prohibit what is permitted by 300.3(B)(3).
Note that the CMP does not agree with me, but I don't see how you can apply the words any other way.

 

[don_resqcapt19]

I have no idea why CMP3 does not understand that 300.3(B)(3) permits an isolated phase installation in any location. Note that the panel comment did not really address my substantiation. If they did not agree with the substantiation, they should have told me that 300.3(B)(3) does not apply in all locations.

3-11 Log #2229 NEC-P03 Final Action: Reject
(300.3(B)(1) Exception)
____________________________________________________________
Submitter: Donald A. Ganiere, Ottawa, IL
Recommendation: Delete the following:
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).

Substantiation: The exception is not required. Such installations are permitted by 300.3(B)(3) in all locations, not just underground locations.

Panel Meeting Action: Reject

Panel Statement: This exception is necessary to permit installations where nonmetallic raceways are installed in close proximity with all of Phase A in one raceway, all of Phase B in another raceway, all of Phase C in another, and all the grounded conductors in another raceway. Where this is useful is between underground manholes so the phase conductors can exit the raceways and be easily racked within the manhole, taking up less space, and making it easier to do testing and maintenance on the installation. This would not be permissible without this exception.
Number Eligible to Vote: 13
Ballot Results: Affirmative: 13

 

[iwire]

The wording in 300.3(B)(3) clearly permits isolated phase installations in any location.

Under certain conditions I have to agree with you.

Note that the CMP does not agree with me, but I don't see how you can apply the words any other way.

Because they feel the rules for parallel conductors take precedent and IMO so will most inspectors.

It may not be correct but it is IMO the reality of the situation.

Already answered...

10/4

I have no idea why CMP3 does not understand that 300.3(B)(3) permits an isolated phase installation in any location.

I think they look at that section as applying only to non-parallel instantiations due to the specific rules for parallel conductors. I also believe that right or wrong most inspectors will see it the way the CMP sees it.

I do not think you or Smart$ are doing Carultch any favors by presenting this option as a sure thing. At the very least that option should be prefaced by 'Talk to the AHJ before spending a dime'.

 

[iwire]

Not relevant to the OP's problem, but MI cable comes to mind.

I am not following you. :huh:

 

[Smart $]

...
I think they look at that section as applying only to non-parallel instantiations due to the specific rules for parallel conductors. I also believe that right or wrong most inspectors will see it the way the CMP sees it.

I do not think you or Smart$ are doing Carultch any favors by presenting this option as a sure thing. At the very least that option should be prefaced by 'Talk to the AHJ before spending a dime'.

You said it... but then again, it is your opinion. :blink:

FWIW, I did point out that he must be in compliance with both 300.3(B)(1) & (3)... which amounts to being compliant with both the parallel rule and the non-ferrous rules. Also pointed out there is no way such would be compliant with 3 sets of 3 circuit conductors divvied up into 2 conduits.

 

[iwire]

You said it... but then again, it is your opinion. :blink:

I don't know what you are trying to say or imply.

 

[Smart $]

I don't know what you are trying to say or imply.

On that remark, I was referring to the underlined portion of quote.

 

[GoldDigger]

I am not following you. :huh:

Just thinking that MI is usually single conductor not requiring a raceway and therefore "intrinsically" isophase.

 

[Smart $]

Just thinking that MI is usually single conductor not requiring a raceway and therefore "intrinsically" isophase.

I don't believe it's an option in this case. I gather there's already two PVC conduits in place going from enclosure to enclosure.

Also, to use MI-MS cable would require completely new enclosure penetrations and would be quite difficult (read impossible without moving enclosures) installing in the most direct route if <= 24" between enclosures.