Parallel feeders and is corresponding Ground conductors 250.122 (c) and (f) and 310.10 (H) 1

JBUDA54 · Aug 31, 2016

We have multiple feeders from a piece of SWGR to multiple SWBDs. These feeders are 1600A’s each so we are running parallel feeders using a separately run #4/0 AWG Ground. The Contractor wrote an RFI in order to try a save the owner money and requested that we run a single ground cable for the multiple feeders and tap off the single ground into the SWBDs instead of running individual grounds back to the SWGR. His justification was that it met Article 250.122 (c). My initial thought was that this is something that can save money and seems to make sense in doing as such. I believe that further down in that article in 250.122 (f) for parallel feeders it points to article 310.10(h) and stipulates that the parallel feeder (phase, neutral, and ground) must adhere to 310.10 (h) (2) which says it must have the same length, consist of the same material, be the same size, have the same insulation, and be terminated in the same manner. This reads to me that the contractor’s suggestion is not allowed because the same length and circular mill, and being terminated in the same manner would not be satisfied.

Am I reading the code properly or is this not it’s intent?

dpc · Sep 27, 2016

Are these "parallel" feeders in multiple conduits? If so, you must run a separate full sized ground wire in each conduit. I'm not sure what you mean by "separately run" ground wire, but the ground wire must be in the same conduit as the phase conductors to be an effective ground return path. I'm too lazy to research the NEC for you, but if you're running these feeders in conduit, I'm pretty sure it requires each conduit to have its own equipment grounding conductor. Regardless of what the Code says, however, it is good engineering practice to put a ground wire in each conduit when there are multiple conduits in a feeder.

HCBFlash · Nov 20, 2016

Interesting.
I find myself "building per print", and questioning things less and less as the years pass, but I can say that only very, very rarely (if ever) do I recall having dealt with equipment grounding conductors of the same circular mils, length, etc., as the phase conductors in parallel feeders. These installations are all inspected by people whose lives revolve around the "NEC". I'm too lazy also to go digging through my books and references right now, but 310.10(h)(2) is certainly applicable in very specific instances only. I'm curious about what you found out and how your own application was resolved.

.

Me wrong? I'm just fine-tuning my sarcasm!

JBUDA54 · Nov 21, 2016

>>>HCBFlash (Electrical)20 Nov 16 18:41
>>>Interesting.
>>>I find myself "building per print", and questioning things less and less as the years pass, but I can say that only very, very rarely (if ever) do I >>>recall having dealt with equipment grounding conductors of the same circular mils, length, etc., as the phase conductors in parallel feeders. These >>>installations are all inspected by people whose lives revolve around the "NEC". I'm too lazy also to go digging through my books and references right >>>now, but 310.10(h)(2) is certainly applicable in very specific instances only. I'm curious about what you found out and how your >>>own application was resolved.

Everytime you have to run feeders above the ampacity of a single conductor cable you run into this situation which in my industrial line of work is very often. I have never been asked by a contractor to splice the grounding conductors on major feeders but on the surface it seems to be something that could be a cost savings approach as long as the NEC allowed it. The direction I gave was for the contractor to route vertical trays into the switchboard instead of conduit as to allow the single EGC in the tray versus having to run the EGC in each of the set of conductors in order to satisfy the NEC 310.10(h)(2).

Thanks dpc and HCBFlash for taking the time in providing me your thoughts on the matter!

dpc · Nov 23, 2016

Just to clarify, by "full-sized" ground conductor, I mean each ground conductor in each conduit must be sized per applicable NEC table (Article 250) as it was the only ground wire. I did not mean to imply that the ground wire had to be equal in size to the phase conductors. It may be, but it is sized per Article 250 for the total circuit rating.

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Parallel feeders and is corresponding Ground conductors 250.122 (c) and (f) and 310.10 (H) 1

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