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250.122 [B] #194781 06/22/10 11:44 AM
Joined: Nov 2007
Posts: 763
KJay Offline OP
How are you interpreting “equipment grounding conductors, where installed,” as stated in 250.122[B] when ungrounded conductors are upsized?
Do you consider this as meaning where an EGC is actually pulled in a raceway, or simply where any EGC is present, whether physically pulled or part of a listed cable assembly, such as SER?

It seems that this could possibly be interpreted either way and might allow using an upsized cable assembly containing an equipment-grounding conductor sized only per Table 250.122, as opposed to a raceway where the conductors are pulled and the EGC sized on the ratio of the circular mil area of the upsized ungrounded conductors.
What is your take on this?


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Re: 250.122 [B] [Re: KJay] #194783 06/22/10 12:37 PM
Joined: Jul 2004
Posts: 9,569
gfretwell Offline
In a cable, the EGC size gets bigger in proportion to the other conductors getting bigger so 250.122(B) is satisfied.
I assume that is built into the listing standard for all cables.
In the case of SE cable (TYLZ in the white book) it says

Based upon tests which have been made involving the maximum heating
that can be produced, an uninsulated conductor employed in a service
cable assembly is considered to have the same current-carrying capacity as
the insulated conductors even though it may be smaller in size.

Greg Fretwell
Re: 250.122 [B] [Re: gfretwell] #194784 06/22/10 02:58 PM
Joined: Nov 2007
Posts: 763
KJay Offline OP
Thank you Greg. Good find on the SE cable listing.
I had considered that the cables must have had this rule applied already, but now that I have thought this through a bit more, it appears that since Table 250.122 is based on overcurrent, not wire size, it wouldn’t have any relevance when over sizing conductors for things such as voltage drop calcs, being that the actual overcurrent protection would normally be lower than the maximum rating of the conductor.
Unfortunately, sometimes I’m not the sharpest tool in the shed.

Re: 250.122 [B] [Re: KJay] #194788 06/22/10 05:12 PM
Joined: Jul 2004
Posts: 9,569
gfretwell Offline
The white book is a great resource if you are curious about the listing on a particular product. Unfortunately it usually ends up making you want to actually see the listing standard and U/L charges big bucks for that.
I suppose that is why they give the White Book away for free. wink

Greg Fretwell


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