Equipment Grounding Conductor in Parallel Raceways

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jclint07

Member
Location
south missouri
It has been a while since my last topic but I have an EGC issue I would like comments on, involving a subpanel being fed by parallel feeders.

A new 400A 120/240V, single phase service disconnect is installed outside on the building.
From there, 2 paralleled raceways (Stabiloy cable with (3) 250AL & (1) #2AL each) feed a 400A rated indoor sub panel, roughly 15 feet inside the building from the service disconnect.

My question is does the #2AL in EACH cable meet the requirement for the EGC size, being it is on a 400A main disconnect? I say no.
250.122(F) states that when multiple parallel cables are used, the EGC shall be run in PARALLEL also, in each raceway and sized per 250.122.
I am being told that they are in compliance because there IS an EGC in each raceway per 250.122(F) and that the circular mil area of both #2AL EGC meet the circular mil area of (1) #1AL which makes them in compliance, per Section 310.4(E). I have never come across such an install. In the past, each EGC in each parallel raceway/cable was always sized per table 250.122 regardless of the actual combined circular mil area of both EGC.
 

Smart $

Esteemed Member
Location
Ohio
You are correct.

The "theory" basis is a line-to-ground fault (just one of the line conductors) can be supplied current from both directions in parallel wiring. Therefore the grounding conductor must be sized for the OCPD rating per T250.122.

However, whoever decided on that as the "theory" basis did not account for the grounding conductor also being parallel, and handling the current in both directions also. The other side of that coin is an assumption that the grounding conductor could be compromised in one of the two directions available.
 
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MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
It has been a while since my last topic but I have an EGC issue I would like comments on, involving a subpanel being fed by parallel feeders.

A new 400A 120/240V, single phase service disconnect is installed outside on the building.
From there, 2 paralleled raceways (Stabiloy cable with (3) 250AL & (1) #2AL each) feed a 400A rated indoor sub panel, roughly 15 feet inside the building from the service disconnect.

My question is does the #2AL in EACH cable meet the requirement for the EGC size, being it is on a 400A main disconnect? I say no.
250.122(F) states that when multiple parallel cables are used, the EGC shall be run in PARALLEL also, in each raceway and sized per 250.122.
I am being told that they are in compliance because there IS an EGC in each raceway per 250.122(F) and that the circular mil area of both #2AL EGC meet the circular mil area of (1) #1AL which makes them in compliance, per Section 310.4(E). I have never come across such an install. In the past, each EGC in each parallel raceway/cable was always sized per table 250.122 regardless of the actual combined circular mil area of both EGC.
As a manufacturer of such a product I will tell you that when you purchase MC Feeder Cable you have to know that it is not generally set up to be used for parallel feeder applications. While it can be used as such, many times the manufacturer will need to know so that they can produce a cable with the correctly sized EGC. The language of 250.122(F) is very clear to us manufacturers....so the EGC in each cable would need to be in compliance with 250.122(F), thus 250.122 @ 400A is each cable shall have a 1 AWG AL.

It sounds like to me they are trying to use the last line in 250.122(A) as their explanation. But that "sectioned" is within the single multiconductor cable...not multiple, multiconductor cables.

Soares is a great resource for these things. In fact, the reason for the full sized EGC in each cable is the potential of a line to ground fault the current would feed the fault in multiple directions which would result in the EGC's (either one) having to carry the entire fault under the OCPD activates. Anyway, it would require special purchased MC Cable being produced for the intent.
 

sammyh

Inactive, Email Never Verified
Thanks for the replies. I am just making sure there is not an exception somewhere that I have never come across regarding parallel EGCs.

does 310.10 H 5 seem to account/explain this installation? p.s. I could not find this 310.4 E, you mentioned, in my 2011 nec? was this a 2008 reference?
 
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