triplex parallel feeders for 4.16 kv cables in cable tray do you size the grounds
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Table 250.122, full size, based on OCPD rating (not the load).
However, you have the option to install just one full size EGC as a single conductor... and there is also the possibility that the tray itself will qualify as the EGC.
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- Location
- Illinois
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- retired electrician
If the installation uses a cable or cable assembly and not single conductors, do we have that option?
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- Placerville, CA, USA
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- Retired PV System Designer
Interesting. So if you have a 12 wire cable and use the conductors in parallel to make four parallels of one three wire circuit, you can add a single full sized EGC in the cable? Or could it also be separate in the tray?
The way I read it, if the circuit is paralleled within the same raceway or cable, it would have to be a single conductor within the raceway or cable, even if this raceway or cable is installed in cable tray. Then, regarding cable, we also have 250.122(A) second paragraph which says the EGC can be sectioned in a multiconductor cable... so does that mean we can parallel conductors to form the 'single' EGC...??? Seems to say yes to me!
- Location
- Illinois
- Occupation
- retired electrician
How does that modify 300.3(B)?
- Location
- Massachusetts
A cable is treated differently than conductors.
The key is the parallel conductors are in more than one cable, and also in a cable tray. If the cables were not in cable tray, then each cable would be required to contain a full-size EGC.
What adds complexity to this is when the tray does not extend to the enclosure where the cable (not its conductors) is terminated. Say you drop these cables out of the tray in conduit chase, because the enclosure is some distance away. The EGCs would have to be in the cables... but if the tray extended all the way to the enclosure, a single EGC would be compliant.
I know how you guys are reading it. I know it may take several to many passes to see it. Distinguish the difference is between 250.122(F) first and second sentence. You guys are assuming the parallel conductors in the tray are single conductors... but if you think about it, those single conductors are actually required to be recognized as single conductor cables... and I think you may be able to make the link from there...
- Location
- Illinois
- Occupation
- retired electrician
I read your first post on this issue as saying that you could use a single EGC where you have cables installed in the cable tray. It is my opinion that you can only do that where you install single conductors in the tray. Where cables are installed each cable must have an EGC as part of the cable and that EGC must be sized to comply with 250.122(F).
As far as single conductor cables, I have never really understood the how the code uses the terms cables and conductors, but it is my opinion that a single conductor should never be a cable. A cable should be an assembly of two or more conductors.
Well I'll never be able to convince you if this is your viewpoint.
- Location
- Illinois
- Occupation
- retired electrician
This question has been debated a number of times with no clear result. Maybe it is time that the terms actually be defined in the code. There are a number of code sections where knowing what the code actually means by those two terms is critical to the application of the section.Well I'll never be able to convince you if this is your viewpoint.
Getting back to the question in this thread, if you have installed multi-conductor cables in parallel in the cable tray, 300.3(B) combined with 250.122(F) will require a full size EGC in each of the multi-conductor cables.
Seems like you want the last word on the matter... :roll:
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