250.122(B) Increased in Size

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Dennis Alwon

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Does 250.122(B) mean you only have to increase the egc if there is voltage drop? This is 2014 Nec change.


250. 122 (B) means anytime you increase the size of your ungrounded conductors then you must increase the equipment grounding conductor proportionally no matter what the reason for the increase in conductor size may be
 

Carultch

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Location
Massachusetts
Does 250.122(B) mean you only have to increase the egc if there is voltage drop? This is 2014 Nec change.

If you increase the current carrying wires because of conditions of use alone (sunlight, bundling, etc), then you do not need to increase the EGC for 250.122(B). NEC2014 now clarifies this with a phrase that says ?from the minimum size that has sufficient ampacity for the intended installation.?

If you increase the size of the current-carrying wires because of voltage drop, then you do need to increase the EGC per 250.122(B). Your starting point for doing this, is the minimum local size of wire that you could install, if length and voltage drop were not a factor. Conditions of use and terminations must remain a factor.

If you increase the size of the current-carrying wires because you are planning surplus ampacity for future use, then you would also need to increase the size of the EGC per 250.122(B).

If you increase the size of the current-carrying wires because you have extra wire of a larger size than necessary, left over from a previous job, then you would also need to increase the size of the EGC per 250.122(B).
 
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Carultch

Senior Member
Location
Massachusetts
That article has been there for a long time they just added some wording to help where you start from.

In the case of parallel sets, it gets a little more interesting. How does one determine what counts as ?the minimum size that has sufficient ampacity for the intended installation??

Example: A 400A feeder with 320A continuous load, that you upsize from 1 set of 600 to 2 sets of 400 in separate conduits. Or did I upsize it from 2 sets of #3/0 to 2 sets of 400?
 

electricg

Member
Location
wa
250. 122 (B) means anytime you increase the size of your ungrounded conductors then you must increase the equipment grounding conductor proportionally no matter what the reason for the increase in conductor size may be

It cannot be for any and every reason, the extra language has changed that.
 

Smart $

Esteemed Member
Location
Ohio
It cannot be for any and every reason, the extra language has changed that.
It can be and is.

However, you and Dennis are exhibiting different premises of determination.

Here's how to look at it...

If Code permits you to use a smaller conductor, without changing wiring method or other conductor characteristics, your conductor is "increased in size".
 

Smart $

Esteemed Member
Location
Ohio
In the case of parallel sets, it gets a little more interesting. How does one determine what counts as ?the minimum size that has sufficient ampacity for the intended installation??

Example: A 400A feeder with 320A continuous load, that you upsize from 1 set of 600 to 2 sets of 400 in separate conduits. Or did I upsize it from 2 sets of #3/0 to 2 sets of 400?
As noted in my other post, you base it on conductor size without changing wiring method or other conductor characteristics.

In the example used, you base the increase in size to 2 sets of 400kcmil on the smallest permitted by Code using 2 sets, which is 3/0 barring other conditions of use not mentioned.
 

sandsnow

Senior Member
It can be and is.

However, you and Dennis are exhibiting different premises of determination.

Here's how to look at it...

If Code permits you to use a smaller conductor, without changing wiring method or other conductor characteristics, your conductor is "increased in size".

That is a good way to look at it.
 
The NEC? Handbook has an excellent example since the '96 cycle that opened my eyes to this misconceived requirement.
If a 20 amp circuit is increased to #6 (typically for parking lot or street lighting), a #6 Equipment Grounding Conductor (EGC) is required.
The misconception would be that a #10 EGC is misinterpreted as being required as a #6 would normally be put on a 60 amp overcurrent device, improperly sizing the EGC to the normal overcurrent protection device (OCPD) for the #6 circuit conductor being placed on a 20 amp OCPD.
What does not get understood, is that you have to have the conductor sized properly to get the current back to the source so as to get the OCPD to operate properly during a fault event. If the return is too small, it will be more of a load than a fault, thusly, not allowing the OCPD to operate properly.
I highly recommend viewers of this response to review the handbook example for other situations as the misconception is an incorrect interpretation of this requirement.
Please note, nothing in this reply is said about, or intended to talk about voltage drop. Further, the energy conservation codes, at least the Florida Code, requires voltage drop considerations.
 

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Smart $

Esteemed Member
Location
Ohio
....
The misconception would be that a #10 EGC is misinterpreted as being required as a #6 would normally be put on a 60 amp overcurrent device, improperly sizing the EGC to the normal overcurrent protection device (OCPD) for the #6 circuit conductor being placed on a 20 amp OCPD.
What does not get understood, is that you have to have the conductor sized properly to get the current back to the source so as to get the OCPD to operate properly during a fault event. If the return is too small, it will be more of a load than a fault, thusly, not allowing the OCPD to operate properly.
....
While I agree that is what Code requires, think about the justification for other than voltage drop considerations. Using your example, if you place that #6 circuit on a 60A breaker, you'd only need a #10 EGC... but you put it on a 20A breaker and you now need a #6 EGC. That contradicts all logic and the physics behind conductor protection.

Another consideration is that Code has historically avoided any voltage drop requirement for circuit conductors. Requiring an upsized EGC for voltage drop considerations is a contradiction in terms. What if I design my circuit conductors for 10% drop (e.g. circuit conductors only upsized a little). This circuit should actually require a larger EGC than one designed for 3% drop (circuit conductors upsized quite likely a bit more).

Then consider there is no "credit" applied for using a metal wiring method (e.g. RMC) which qualifies as an EGC by itself. A regular sized EGC and RMC together will have lower combined resistance than an upsized EGC by itself in most cases.
 

Carultch

Senior Member
Location
Massachusetts
As noted in my other post, you base it on conductor size without changing wiring method or other conductor characteristics.

In the example used, you base the increase in size to 2 sets of 400kcmil on the smallest permitted by Code using 2 sets, which is 3/0 barring other conditions of use not mentioned.

It would be interesting to see how this applies to an installation of parallel sets, whereby when you calculate the minimum local size at that number of parallel sets ends up being smaller than #1/0.


For instance, a 400A feeder upsized to 4 sets of 300 kcmil. We're talking about a REALLY long feeder, here. In this example, 400A at 4 sets = #2. Four sets of #2 theoretically has the ampacity of 400A, but isn't permitted by the NEC. I suppose the "floor" of your starting point would be "N sets of 1/0", where N is the number of parallel sets in your installation.
 

Smart $

Esteemed Member
Location
Ohio
It would be interesting to see how this applies to an installation of parallel sets, whereby when you calculate the minimum local size at that number of parallel sets ends up being smaller than #1/0.


For instance, a 400A feeder upsized to 4 sets of 300 kcmil. We're talking about a REALLY long feeder, here. In this example, 400A at 4 sets = #2. Four sets of #2 theoretically has the ampacity of 400A, but isn't permitted by the NEC. I suppose the "floor" of your starting point would be "N sets of 1/0", where N is the number of parallel sets in your installation.
You mean 4 sets of #3 is the basic size for 400A.

Upsizing to 4 sets of 300kcmil is a pretty big jump. I'm tempted to say step up-down transformers would likely be used... but that's on the design side rather than a matter of Code compliance

EGC required for 400A is #3 also. So same size as minimum. Upsized to 4 sets at 300kcmil, you'd be required to size both circuit conductors and EGC's at 300kcmil.

I believe we have to use the hypothetical minimum set size as a basis. We can't use the 1/0 as the basis because that requirement is not an adjustment or correction for ampacity. Let's say you ran 4 parallel sets but not for voltage drop. You'd have to use 1/0. Should the 1/0 be considered an "increased in size"? I say yes.
 
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