250.122(B) - increasing size of EGC

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royta

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I think I know the answer already, but I'm looking for reassurement. I'm installing two 20A circuits in a back yard. Due to length of runs, I will need to increase conductors of one of the circuits to #8. According to 250.122(B), I need to divide cmil of #8 by cmil of #12 and multiply the answer by the cmil of the minimum required EGC for a 20A circuit shown in Table 250.122. Great, I get to use #8 for my EGC for a darn 20A circuit.

I have two arguments of why this is crazy.
  1. The #12 EGC requirement for a 20A circuit is already super conservative, and I'm guessing this stems from 240.4(D). I'm wondering why there isn't an exception to 250.122(B) for 15, 20, and 30 amp circuits.
  2. I'll be running these circuits in EMT, and I don't even need to run an EGC according to 250.118(4). However, I like to run EGC's no matter what the conduit type, so because of that, I'm now required to bump the EGC to #8.
 
charlie b

charlie b

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You have it right, including the part about this being crazy.

But you want to know the real crazy part? Depending on what is on the other end of the circuit, you might be able to replace the 20 amp breaker with a 50 amp breaker, and then go back to using a #10 EGC! :roll:
 
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royta

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charlie b said:
You have it right, including the part about this being crazy.

But you want to know the real crazy part? Depending on what is on the other end of the circuit, you might be able to replace the 20 amp breaker with a 50 amp breaker, and then go back to using a #10 EGC! :roll:
Click to expand...

I'm looking forward to what others are doing in this situation. I'm certain this comes up often in the field.
 
infinity

infinity

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I agree with Charlie, you have it right even though it may seem wrong.:rolleyes:

Seems rather crazy that you can install this in EMT without an EGC but when you want to use an EGC it has to be #8 even though it's in parallel with the acceptable metal conduit as an EGC.
 
charlie b

charlie b

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charlie b said:
Depending on what is on the other end of the circuit, you might be able to replace the 20 amp breaker with a 50 amp breaker, and then go back to using a #10 EGC! :roll:
Click to expand...
From the "other related thread," I have learned that these circuits supply receptacle outlets. So you won't be able to use my suggestion of installing a 50 amp breaker. :cool:
 
R

royta

Senior Member
charlie b said:
From the "other related thread," I have learned that these circuits supply receptacle outlets. So you won't be able to use my suggestion of installing a 50 amp breaker. :cool:
Click to expand...

I know, but like you and infinity say, this is just a dumb requirement. By only running #12, I would still be better off than getting away with no EGC, as allowed by 250.118(4), but then I'd be violating the NEC.

Somebody needs to submit a change.
 
George Stolz

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Not to stray off topic, but I was just looking for 2008 proposals to this section, and came across this:
eek.gif



____________________________________________________________
5-281 Log #585 NEC-P05 Final Action: Reject
(250.122(B) Exception (New) )
____________________________________________________________
Submitter: Mr. ------------- Dept. of Transportation
Recommendation: Add exception to 250.122(B) and add FPN to the
exception
Exception: Street lighting, traffic signals, and similar outside branch circuits
not connected to building wiring, where each pole or standard is equipped with
a supplementary grounding electrode that provides effective grounding.
FPN: The effectiveness of supplementary grounding electrodes varies with
soil conditions.

Substantiation: The proposal provides for effective equipment grounding
at lower cost than the existing requirement. The proposal does not require
supplementary grounding electrodes but does waive the requirement for upsized
equipment grounding conductors where the supplementary grounding
electrodes are installed. Also, the proposal legalizes what some jurisdictions do
and will continue to do anyway.

Panel Meeting Action: Reject

Panel Statement: Supplementary grounding electrodes are not permitted
as equipment grounding conductors as indicated in 250.54 and 250.4. The
proposed FPN provides no functionality, clarity, or improvement in usability of
this section. The earth does not provide an effective ground-fault current path.

Number Eligible to Vote: 15
Ballot Results: Affirmative: 15
Click to expand...
Remind me not to touch any poles in Wisconsin!

Anyway, back to look for a similar proposal.

Edit:

I found a similar one, you have an uphill battle on your hands on this one, IMO:

____________________________________________________________
5-282 Log #1262 NEC-P05 Final Action: Reject
(250.122(B) Exception (New) )
____________________________________________________________
Submitter: Nicholas Alger, Modjeski and Masters Inc.

Recommendation: Add an exception to 250.122(B) as follows:
Exception: Equipment grounding conductors shall not be required to be
increased in size where analysis performed under engineering supervision
demonstrates that the impedance of the equipment grounding conductors
remains low enough to facilitate overcurrent protective device operation within
a time period which prevents damage to either the ungrounded conductors or
equipment grounding conductors under line-to-ground fault conditions.


Substantiation: 250.122(B), as currently written, requires an equipment
ground conductor (EGC) to be increased in size proportionately to the
ungrounded conductors irregardless of the reason for increasing the size of the
ungrounded conductors. This provides for a conservative approach to sizing the
EGC in cases where a detailed engineering analysis of the grounding system
under line-to-ground fault conditions is not performed. However, it also has the
undesirable effect of causing an EGC to be increased in size even if an analysis
of grounding system performance shows that this increase is unnecessary.
There are many reasons why a circuit designer may elect to increase the size
of ungrounded conductors. This change would permit the designer to undertake
an appropriate analysis to determine if the EGC should also be increased in
size instead of simply increasing it blindly. Stipulating that such an analysis
may be performed only under “engineering supervision” will prevent
unqualified persons from using this new exception as an excuse for undersizing
an EGC. There is already precedent in the code for allowing such analyses in
lieu of blind application of a rating or requirement (see 310.15(C)).

Panel Meeting Action: Reject
Panel Statement: The panel concludes that the prescriptive text is correct. See
panel action on Proposal 5-276 regarding ampacity adjustments.
Click to expand...
 
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