2014 change to 250.122(B)

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charlie b

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Seattle, WA
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Electrical Engineer
I like the 2014 change to 250.122(B), in which they defined the starting point for upsizing the ungrounded conductors. But I would like some opinions on the new wording. It says you upsize the EGC if the ungrounded conductors have been upsized ?from the minimum size that has sufficient ampacity for the intended installation.? Here is an example:

  • Four identical single phase, 208 volt circuits will be run in the same conduit.
  • The calculated load for each circuit is 46 amps (includes any consideration of continuous loads).
  • I will use a 50 amp, 2-pole breaker for each circuit.
  • The wire will be THHN copper.
  • Looking at table 310.15(B)(16), I see that #8 has an ampacity of 50 amps. However, I know I need to derate for having 8 CCCs in the same conduit.
  • I can use the 55 amp value from the 90C column, and multiply by 70%. That gives me an ampacity of only 38.5. This is not enough for my installation.
  • I next try #6. Derating its 90C value of 75 amps using the 70% factor, I get an ampacity of 52.5. So I decide to use that size wire.

QUESTION:
Do I now have to upsize the EGC from the #10 that would otherwise be appropriate for a 50 amp circuit?
 

bob

Senior Member
Location
Alabama
The requirement is that you start "from the minimum size that has sufficient capacity for the intended installation". Your example requires that you increase the conductor size to meet the minimum capacity and the breaker size remains the same. I would not think an increase on the EGC is necessary.
However, I am not sure if an increase in conductor size for VD would meet the requirement "sufficient capacity for the intended installation".
If so, the problem with this section would be solved.
 

jumper

Senior Member
I looked up the proposal to look at the reasoning for the change. I thought it might add to the discussion.

Here is the proposal:

___________________________________________________
5-199 Log #3077 NEC-P05
Final Action:
Accept in Principle
(250.122(B))
________________________________________________________________
Submitter:
Frederic P. Hartwell, Hartwell Electrical Services, Inc.
Recommendation:
Revise as follows:
(B) Increased in Size.
Where ungrounded conductors are increased in size
from the minimum size that has sufficient ampacity for the intended
installation, equipment grounding conductors, where installed, shall be
increased in size proportionately according to the circular mil area of the
ungrounded conductors.
Substantiation:
This proposal resubmits what would have been the text of the
2011 NEC had CMP 5 reported its action correctly on Proposal 5-290 in that
cycle and maintained that position. The inserted language is simple and clear. It
is pointless and technically incorrect to require an increase in the minimum size
of an equipment grounding conductor, which functions only for a short-time
event and can be insulated or bare, just because some condition of use requires
the ungrounded conductors to increase in size. Example D3(a) does not make
this increase, and it may be necessary to do so if this clarification is not made.
Panel Meeting Action: Accept in Principle
Revise the text of 250.122(B) to read as follows:
(B) Increased in Size.
Where ungrounded conductors are increased in size
from the minimum size that has sufficient ampacity for the intended
installation, wire type equipment grounding conductors, where installed, shall
be increased in size proportionately according to the circular mil area of the
ungrounded conductors.
Panel Statement:
The revised text incorporates the text from proposal 5-198.
Number Eligible to Vote: 16
Ballot Results:
Affirmative: 16
 

charlie b

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Location
Seattle, WA
Occupation
Electrical Engineer
However, I am not sure if an increase in conductor size for VD would meet the requirement "sufficient capacity for the intended installation".
If so, the problem with this section would be solved.
And I agree with both points. A conductor's ampacity does not change with the length of the run, or with the voltage that is available at the end of the run.

 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician

QUESTION:
Do I now have to upsize the EGC from the #10 that would otherwise be appropriate for a 50 amp circuit?

I say no and frequently use this as an example:

6_15_34_3_2.gif


In either case the EGC would be ths same size because you didn't "up-size" anything.
 

Smart $

Esteemed Member
Location
Ohio
No upsizing the EGC required for that scenario. You did not upsize your conductors to an ampacity greater than the minimum size required.

That said, I'd actually like to see the upsizing changed to being based on the maximum standard OCPD rating that could protect the upsized conductors. For example, say your proposed scenario required you to go with #2 THHN to compensate for voltage drop. Derating for CCC's: 130A ? 70% = 91A. The maximum standard OCPD rating that you could protect this conductor with is 100A. Per Table 250.122, you'd only have to run a #8 EGC... and not a #6.
 

bob

Senior Member
Location
Alabama
That said, I'd actually like to see the up sizing changed to being based on the maximum standard OCPD rating that could protect the up sized conductors. For example, say your proposed scenario required you to go with #2 THHN to compensate for voltage drop. Dratting for CCC's: 130A ? 70% = 91A. The maximum standard OCPD rating that you could protect this conductor with is 100A. Per Table 250.122, you'd only have to run a #8 EGC... and not a #6.

In Charlie's example, he only needs a 50 amp breaker. If he needed to increase the size to #2 for VD, there is no need to change the EGC from #10 to #8 unless there is some reason #10 does not provide an adequate low impedance path to trip the breaker.
 

Smart $

Esteemed Member
Location
Ohio
In Charlie's example, he only needs a 50 amp breaker. If he needed to increase the size to #2 for VD, there is no need to change the EGC from #10 to #8 unless there is some reason #10 does not provide an adequate low impedance path to trip the breaker.
I realize that... my proposal was a compromise (#8), between no upsizing (#10) and current requirement (#6).
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
The absurdity of 250.122(B)......
Inspector: "your EGC of #6 on this circuit with a 110 breaker is too small because you used 3/0 conductors".
Electrician: "OK, I'll change the breaker to a 200. Now I'm compliant".
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The absurdity of 250.122(B)......
Inspector: "your EGC of #6 on this circuit with a 110 breaker is too small because you used 3/0 conductors".
Electrician: "OK, I'll change the breaker to a 200. Now I'm compliant".
"And I will put a 110A breaker at the other end to satisfy the OCPD requirement on the connected load...."

(Interesting scenario: If a tap rule lets you use a smaller conductor than the feeder breaker, would the EGC upsize then take effect if you did not use the smallest conductor that the tap rule would allow?)
 

Smart $

Esteemed Member
Location
Ohio
...
(Interesting scenario: If a tap rule lets you use a smaller conductor than the feeder breaker, would the EGC upsize then take effect if you did not use the smallest conductor that the tap rule would allow?)
With taps you have to use a full size feeder EGC for the tap conductor EGC... but not larger than the tap conductor. So it wouldn't affect a tap.
 

Smart $

Esteemed Member
Location
Ohio
The absurdity of 250.122(B)......
Inspector: "your EGC of #6 on this circuit with a 110 breaker is too small because you used 3/0 conductors".
Electrician: "OK, I'll change the breaker to a 200. Now I'm compliant".
Another reason for the 'compromise'... when you do cross OCPD rating thresholds. Your example does not cross a threshold.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
"And I will put a 110A breaker at the other end to satisfy the OCPD requirement on the connected load...."

(Interesting scenario: If a tap rule lets you use a smaller conductor than the feeder breaker, would the EGC upsize then take effect if you did not use the smallest conductor that the tap rule would allow?)

Yes, you are correct if it is a branch circuit. But I was thinking of, say a panelboard that has a 200 amp rating.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Table 250.122 just needs to be replaced with a table that works like Table 250.66. You would look at the ungrounded conductor size and read the table to find the EGC.

Of course we would need some language to cover things like tap circuit and circuits with conductors that are connected in parallel.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
Interesting scenario: If a tap rule lets you use a smaller conductor than the feeder breaker, would the EGC upsize then take effect if you did not use the smallest conductor that the tap rule would allow?
Troublemaker! :happyyes: Actually, the answer is no. The tap rules allow us to use smaller conductors, but they do not reestablish the ampacity of the smaller conductors. The thing that triggers a larger EGC is using an ungrounded conductor that has a higher ampacity than is required for the installation.

 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Troublemaker! :happyyes: Actually, the answer is no. The tap rules allow us to use smaller conductors, but they do not reestablish the ampacity of the smaller conductors. The thing that triggers a larger EGC is using an ungrounded conductor that has a higher ampacity than is required for the installation.

But what I am saying is that if I choose not to take advantage of the tap rule, I would then be using a larger conductor and ampacity than "required". The EGC upsize provision thus forces us to figure out what combination of rules results in the lowest possible required ampacity for a given configuration.
 

Smart $

Esteemed Member
Location
Ohio
Table 250.122 just needs to be replaced with a table that works like Table 250.66. You would look at the ungrounded conductor size and read the table to find the EGC.

Of course we would need some language to cover things like tap circuit and circuits with conductors that are connected in parallel.
Just change the left column heading...

Conductor Ampacity*
15
20
...
...
5000
6000
*After application of adjustment and correction factors.
 
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