Upsizing EGC with conductor size?

[Npstewart]

I will concede that this is the one thing that always confused me. It made me wonder why 250.122(B) was ever put into the code. Changing from #12 to #10 phase conductors will reduce the overall circuit impedance, increase the available fault current, and cause the OCPD to respond more rapidly. Why then, do we need to reduce the fault circuit impedance even further by using a #10 EGC?

This is speculation, but perhaps this was put into the code to account for future. If someone sees a #10 they wont think twice about changing the circuit breaker from 20A to 30A for a different load in order to re-use the branch circuit, and having a #12 EGC likely wouldn't stop them.

 

[jaggedben]

.. Nevertheless, getting back to Charlie's Rule, "The words are what the words are."

Yes, let's get back to the words of the code, namely the definition of a Qualified Person, which most certainly does not require an engineering degree in all cases. And the words of the exception, which does not require written permission.

I have already given my opinion on the qualifications needed to take advantage of the exception.

 

[LarryFine]

This is speculation, but perhaps this was put into the code to account for future. If someone sees a #10 they wont think twice about changing the circuit breaker from 20A to 30A for a different load in order to re-use the branch circuit, and having a #12 EGC likely wouldn't stop them.

Which is what I said way back in post #15.

 

[Npstewart]

Which is what I said way back in post #15.

I didn’t see it, but you’ve got a good head on your shoulders. Genius.


Sent from my iPhone using Tapatalk

 

[charlie b]

Do I understand this correctly? If a licensed journeyman or contractor electrician does a calculation and writes it down, and signs it with their name and license number, it can't be an "official document" simply because it's not signed by a licensed PE?

You are not understanding the point I'm trying to make. I believe an electrician, regardless of experience, does not have the qualifications needed to confirm that the resistances, inductive reactances, circuit lengths, conduit materials, and the details of the voltage source are sufficient to provide an effective ground fault pathso as to skip uosizing tge EGC.. Most PE EEs don't either.

 

[LarryFine]

I didn’t see it, but you’ve got a good head on your shoulders. Genius.

Flattery will get you everywhere.

 

[charlie b]

As a licensed PE, could you simply add your signature and seal to the document, and then it becomes an official document? I understand you probably don't want to do that without charging for the servIce.

As a licensed PE, I would be fined and perhaps lose my license for doing that. And it's not about being paid. If I cannot declare that, "This work was done by me or under my supervision," I am not allowed to seal and sign the document

 

[jaggedben]

This is speculation, but perhaps this was put into the code to account for future. If someone sees a #10 they wont think twice about changing the circuit breaker from 20A to 30A for a different load in order to re-use the branch circuit, and having a #12 EGC likely wouldn't stop them.

You should always think twice about changing the OCPD on a circuit. If someone only looks at the wire size on the OCPD, then in my opinion that person is *not* a qualified person. Just my opinion. ;-)

 

[charlie b]

Yes, let's get back to the words of the code, namely the definition of a Qualified Person, which most certainly does not require an engineering degree in all cases. And the words of the exception, which does not require written permission.

You need to be qualified for the task at hand. You might be qualified to perform general residential wiring, but not to work with HVAC, medium voltage, or overhead wiring. Demonstrating that the ground fault path is sufficient to cause the OCPD to act quickly enough does not, in my opinion, fall within the qualifications of an electrician.

If you upsize the EGC per the code requirements, you can be sure it will be OK. If instead you wish to not upsize the EGC per the exception, you will need something more than the invalid "begging the question" concept I described in post #35.

 

[jaggedben]

You are not understanding the point I'm trying to make. I believe an electrician, regardless of experience, does not have the qualifications needed to confirm that the resistances, inductive reactances, circuit lengths, conduit materials, and the details of the voltage source are sufficient to provide an effective ground fault pathso as to skip uosizing tge EGC.. Most PE EEs don't either.

So going back to some of the above discussion with Wayne, please explain how any of those things make a difference if, say, the circuit length is less than 100ft, the conductors are not in the kcmil range, and the voltage is 1000V or less.

A big part of the problem here is that 250.122(B) only excepts ampacity calculations from the reasons for upsizing, while there are other legitimate reasons to do so that shouldn't affect the table. A big one is terminal wire size specs. I might have a very legitimate reason to run a 50A OCPD circuit to a piece of a equipment (say, a common 125A subpanel) whose lugs are specified for minimum 4awg. But I'm supposed to upsize my EGC from a #10 to a #6 because the circuit conductors were upsized two regular sizes? Even though if the #4s were used at their full amapcity I'd only need a #8? And anyone who knows ohms law understands that it makes no damn difference to whether the breaker will trip?

Downsizing the breaker on an existing circuit, as Strathead mentioned above, is also a big one (something I do not infrequently for article 705 reasons). There is no way that lowering the rating of the OCPD on a previously compliant circuit can ever make the situation more dangerous. I think that's true at just about any length and voltage. Do you disagree?

 

[jaggedben]

You need to be qualified for the task at hand. You might be qualified to perform general residential wiring, but not to work with HVAC, medium voltage, or overhead wiring...

...

I completely agree. Which is to say, the qualifications needed depend on the context and in many situations do not rise to needing an engineering degree.

 

[LarryFine]

Not every fault is a bolted fault. Some may result in a relatively long duration.

 

[wwhitney]

I believe an electrician, regardless of experience, does not have the qualifications needed to confirm that the resistances, inductive reactances, circuit lengths, conduit materials, and the details of the voltage source are sufficient to provide an effective ground fault path.

Agreed.

Fortunately, electricians don't have to do this calculation from scratch. The scenarios in which an electrician would reasonably invoke 250.122(B) exception are of the form "Scenario A involving a minimum size EGC obviously provides an effective ground fault path. My installation differs from Scenario A only in ways that will decrease the ground fault impedance. Therefore it provides an effective ground fault path."

Cheers, Wayne

 

[charlie b]

So going back to some of the above discussion with Wayne, please explain how any of those things make a difference if, say, the circuit length is less than 100ft, the conductors are not in the kcmil range, and the voltage is 1000V or less.

There is no way that lowering the rating of the OCPD on a previously compliant circuit can ever make the situation more dangerous. I think that's true at just about any length and voltage. Do you disagree?

To the first, I say, "no difference." To the second, I say, "I agree."

But they can't write code articles in the style of, "i before e, except after c, or when sounding like a as in neighbor or weigh." They can't compose a rule that says anything like, "upsize the EGC except for 20 amp circuits shorter than 100 feet, or 30 amp circuits shorter than 150 feet, or (fill in as many except-for items as you wish)."

Bottom line: In order for the code to be capable of being followed and enforced, it will sometimes be inconvenient.

 

[jaggedben]

Not every fault is a bolted fault. Some may result in a relatively long duration.

In which case, all else being equal, larger circuit conductors with the same OCPD and EGC will trip faster, if there's any difference. By themselves, the larger circuit conductors only make the situation safer. This is why this code section is so backwards.

The only reason an EGC needs to be upsized is voltage drop. This code section used to say that, and it should go back to saying that, and leave it up to the AHJ to determine if the true reason for larger conductors was voltage drop. Or perhaps the code should invoke the length of the circuit. But it should not sweep up all the other possible legitimate reasons that conductors end up larger than 310 requires.

 

[jaggedben]

To the first, I say, "no difference." To the second, I say, "I agree."

Thank you.

But they can't write code articles in the style of, "i before e, except after c, or when sounding like a as in neighbor or weigh." They can't compose a rule that says anything like, "upsize the EGC except for 20 amp circuits shorter than 100 feet, or 30 amp circuits shorter than 150 feet, or (fill in as many except-for items as you wish)."

Bottom line: In order for the code to be capable of being followed and enforced, it will sometimes be inconvenient.

This code section used to apply only to conductors upsized for voltage drop, and it should go back to saying that, and leave it up to the AHJ to determine if the true reason for larger conductors was voltage drop. They could leave the exception in but change it to 'engineering supervision' to recognize what you've been saying.

 

[Strathead]

Strathead, I welcome all opinions and cherish everyone's right to disagree. I also honor and respect the knowledge and experience it takes a person to become a Journeyman or Master Electrician. I would never question such a person's qualifications to design and install electrical equipment. But those qualifications are not the same as would be needed to ascertain that an effective ground fault return path exists even if you don't upsize the EGC. See my post #14 for my reasoning.

The science of logical reasoning (OK, I recall this from a college course I took 50 years ago) includes several "classical" invalid arguments. One goes something like this:
Person 1 - "What needs to be done here is XXX."
Person 2 - "Can you prove that?"
Person 1 - "This is my area of expertise. I am fully qualified to make this call. Trust me."

It may turn out that Person 1 is right. But the proof totally failed to prove anything. This type of invalid reasoning is called, "begging the question." This is what comes to my mind when I read statements along the lines of, "I am qualified enough to know I don't have to upsize my ground." How would a reviewer know who made the call not to upsize? How would a reviewer know that person's qualifications? A PE has the privilege (and indeed the duty) to declare to the world (by sealing and signing design documents) that, "This work was done by me or under my supervision." Is that needed, in order to take advantage of the exception under discussion here? I think so. You and others have disagreed.

Bottom line: If I am performing a plan review, or perhaps an on-site inspection of an installation in progress, and I see a 20 amp circuit with #10 phase and neutral conductors and a #12 EGC, and if there is no written justification for not using a #10 EGC, then I will cite this as a code violation.

Did you read my examples? I have read through the subsequent quotes. I agree with you in the narrow scope you are addressing, however, in my first example, if you are the engineer, are you telling me you couldn't make that call? If I were the owner and we were talking about the money coming out of my pocket I would be unsatisfied with your service. There is NO JUSTIFICATION to change that ground, and to the best of my understanding, that is exactly the type of situation the code change was put in place for.

 

[tortuga]

If you guys are interested in some historical context the modern Table 250.122 came from a UL proposal in the 1969 NEC. However our friends up north in Canada never adopted this and to this day use smaller EGC's, Here is their version of 250.122 (table 16):

 

[charlie b]

This code section used to apply only to conductors upsized for voltage drop, and it should go back to saying that, and leave it up to the AHJ to determine if the true reason for larger conductors was voltage drop.

They changed it because installers "cheated" the system by saying such things as, "It wasn't for voltage drop, it was just the only wire I had in the truck."

 

[charlie b]

Did you read my examples? I have read through the subsequent quotes. I agree with you in the narrow scope you are addressing, however, in my first example, if you are the engineer, are you telling me you couldn't make that call?

I did read your examples. For the first example, I also consider myself qualified enough to recognize that the situation was ridiculous. I strongly believe that not upsizing the EGC when the breaker was dialed down to 150 amps would not create a safety hazard. It would, however, create an undesirable opportunity for confusion (e.g., Who made this decision? Did he make an error? Why did he do that? Is this really code-compliant? Do we need to fix this?).

Could I make that call? Yes. Would I make that call? No, at least not without leaving something on the record as justification that future reviewers could evaluate for themselves. And that "something" would have to be stronger than, "Trust me, I know what I am doing."