Parallel Feeder in Cable Tray

[nhee2]

I have seen a number of posts regarding the fact that tray cable, when used for parallel runs for a large feeder, will likely not meet the EGC sizing requirements of 250.122(F) for a full sized EGC with each parallel set of conductors. How do most of you specify the conductor config in these situations? Parallel single conductors? Use the tray as the EGC? Ignore the requirement and use 'standard' tray cable? Something else?

 

[Carultch]

I have seen a number of posts regarding the fact that tray cable, when used for parallel runs for a large feeder, will likely not meet the EGC sizing requirements of 250.122(F) for a full sized EGC with each parallel set of conductors. How do most of you specify the conductor config in these situations? Parallel single conductors? Use the tray as the EGC? Ignore the requirement and use 'standard' tray cable? Something else?

I'm curious to know too.

My suggested strategy would be to run the required EGC as a separate conductor, in the same tray. Then tie the cables' factory EGCs to ground on exclusively one side, while wire nutting them to nothing on the opposite end. Any solution needs to be confirmed with your AHJ. If your AHJ requires them connected on both sides, and you do the above, it is simple enough to connect them. It is my understanding that no single EGC path in a parallel group of EGCs may be insufficiently sized, which is the case if you were to connect the factory EGC's to both ends, thus why I suggest the "no connect" on the opposite side.

 

[roger]

Usually I use single conductors due to the fact that specially built cables have a minimum order length.

Roger

 

[nhee2]

Usually I use single conductors due to the fact that specially built cables have a minimum order length.

Roger

Thanks.

Do you include single EGC in the tray? Paralleled single conductor EGCs? Use the tray as EGC?

 

[jap]

I'm curious to know too.

My suggested strategy would be to run the required EGC as a separate conductor, in the same tray. Then tie the cables' factory EGCs to ground on exclusively one side, while wire nutting them to nothing on the opposite end. Any solution needs to be confirmed with your AHJ. If your AHJ requires them connected on both sides, and you do the above, it is simple enough to connect them. It is my understanding that no single EGC path in a parallel group of EGCs may be insufficiently sized, which is the case if you were to connect the factory EGC's to both ends, thus why I suggest the "no connect" on the opposite side.

:?


JAP>

 

[roger]

Thanks.

Do you include single EGC in the tray? Paralleled single conductor EGCs? Use the tray as EGC?

Yes, a single EGC sized to the largest feeder or branch circuit in the tray.

Roger

 

[dkidd]

:?


JAP>

+1

 

[Carultch]

:?


JAP>

You'll have to ask a more specific question, if you'd like me to answer.

Do you know any better solution, when the manufactured cable doesn't have a large enough EGC, other than "do not use a manufactured cable"?

 

[iwire]

You'll have to ask a more specific question, if you'd like me to answer.

Do you know any better solution, when the manufactured cable doesn't have a large enough EGC, other than "do not use a manufactured cable"?

In my opinion there is no code compliant way to use the cable, your suggestion is a direct violtion of 300.3(B).

 

[texie]

I have seen a number of posts regarding the fact that tray cable, when used for parallel runs for a large feeder, will likely not meet the EGC sizing requirements of 250.122(F) for a full sized EGC with each parallel set of conductors. How do most of you specify the conductor config in these situations? Parallel single conductors? Use the tray as the EGC? Ignore the requirement and use 'standard' tray cable? Something else?

As you indicate, this has been a tough issue to deal with short of ordering special cable. It seems that the 2017 NEC now gives some relief. See 250.122(F)(2) which is new to accommodate this problem.
Not sure of your code year but maybe the AHJ would honor the 2017 language.

 

[nhee2]

Yes, a single EGC sized to the largest feeder or branch circuit in the tray.

Roger

Thanks, this is what I was intending to recommend for an installation we are looking at.

For installations that you encounter (but don't specify or install) do you frequently find that existing installations do not comply with 250.122F? I have encountered several proposed/existing installs recently where the requirement for full sized EGC was not followed.

 

[Carultch]

In my opinion there is no code compliant way to use the cable, your suggestion is a direct violtion of 300.3(B).

300.3(B) gives a list of all the wiring methods, when it says "all circuit conductors including the EGC must be contained in the same X". And it gives an "or" statement when it lists them, meaning they can be contained in any of the wiring methods listed.

What I suggest would still put them in the same "parent wiring method" (i.e. cable tray), albeit not inside the same "child wiring method" (i.e. cable). This was the conclusion the last time we had this discussion on this forum, and it had been accepted by the AHJ in question. Obviously they won't all accept it. I know it is a stretch to see the words this way.

 

[iwire]

What I suggest would still put them in the same "parent wiring method" (i.e. cable tray), albeit not inside the same "child wiring method" (i.e. cable). This was the conclusion the last time we had this discussion on this forum. I know it is a stretch.

I do not see the harm in using the cable, but IMO more than a stretch for the AHJ to allow it.

This same issue hits us all the time with SER for large temps and sometimes with MC for large feeders.

336.2 Definition.
Power and Control Tray Cable, Type TC. A factory assembly
of two or more insulated conductors, with or without
associated bare or covered grounding conductors, under
a nonmetallic jacket.

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
shall be contained within the same raceway, auxiliary
gutter, cable tray, cablebus assembly, trench, cable, or
cord, unless otherwise permitted in accordance with
300.3(B)(1) through (B)(4).

Of course there is this

(3) Nonferrous Wiring Methods. Conductors in wiring
methods with a nonmetallic or other nonmagnetic sheath,
where run in different raceways, auxiliary gutters, cable
trays, trenches, cables, or cords, shall comply with the provisions
of 300.20(B). Conductors in single-conductor Type
MI cable with a nonmagnetic sheath shall comply with the
provisions of 332.31. Conductors of single-conductor Type
MC cable with a nonmagnetic sheath shall comply with the
provisions of 330.31, 330.116, and 300.20(B).

But it does not apply to a single cable tray.


Its a real road block when trying to do things quickly.

Perhaps buy a tray cable with an extra, full size conductor and strip it bare / tape it green at each termination?

 

[jap]

300.3(B) gives a list of all the wiring methods, when it says "all circuit conductors including the EGC must be contained in the same X". And it gives an "or" statement when it lists them, meaning they can be contained in any of the wiring methods listed.

What I suggest would still put them in the same "parent wiring method" (i.e. cable tray), albeit not inside the same "child wiring method" (i.e. cable). This was the conclusion the last time we had this discussion on this forum, and it had been accepted by the AHJ in question. Obviously they won't all accept it. I know it is a stretch to see the words this way.

Then tie the cables' factory EGCs to ground on exclusively one side, while wire nutting them to nothing on the opposite end. Any solution needs to be confirmed with your AHJ. If your AHJ requires them connected on both sides, and you do the above, it is simple enough to connect them. It is my understanding that no single EGC path in a parallel group of EGCs may be insufficiently sized, which is the case if you were to connect the factory EGC's to both ends, thus why I suggest the "no connect" on the opposite side.

 

[jap]

Disregard my last post.

It was a misfire.

JAP>

 

[electrofelon]

I would just add that the EGC in a cable is often big enough for several parallel runs, so dont just assume its a deal breaker. I used to think that cables were pretty much out for parallel runs or upsizing for VD, but its actually often not. Just a few examples: Say I want an 800 amp feeder, I could use 4 parallel 250-X SER, which has a 3/0 ground, which meets the requirement.
Say I am going up to 1/0 from #6 for VD. I would need a #2, which is what is in 1/0 SER. I certainly am not saying it always works, but it may be fine more often than you think.

 

[nhee2]

As you indicate, this has been a tough issue to deal with short of ordering special cable. It seems that the 2017 NEC now gives some relief. See 250.122(F)(2) which is new to accommodate this problem.
Not sure of your code year but maybe the AHJ would honor the 2017 language.

Thanks for pointing out the revised code section. This installation is 2014 NEC, however I think the 2017 changes may be acceptable.

2017 250.122(F)(2) (b) looks like it is allowing for all multiconductor cable EGC's to be connected in parallel with a single, full size EGC run with the cables. And 250.122(F)(2)(d) says that the multiconductor cable EGCs do not have to be full sized.

250.122(F)(2)(c) looks like I could use the tray as my EGC.

Does this sound correct?

For installations where we transition from tray to multiple conduits and into the equipment - Is the new section allowing me to use the conduit as my EGC? Requiring me to run a full size EGC in this section? It is not clear to me.