DIY install, help me be as code compliant as possible please

[wwhitney]

"Article 250.122(B) (Increased in Size): Where ungrounded conductors are increased in size..." does not appear to me to fit this situation, i.e. this circuit is new and therefore Table 250.122 (Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment) should apply.

If I understand correctly, you are suggesting that "increased in size" applies only to a rewiring situation, where you pull out one set of wires and put in another. That doesn't really make any sense from an electrical point of view--the adequacy or inadequacy of a given size EGC doesn't depend on what previous installation was there. I interpret "increased in size" to mean "larger than the minimum size for a given breaker and wire insulation type." I believe this to be the generally accepted understanding of that phrase as used in 250.122(B).

For more commentary on this or other NEC issues, see forums.mikeholt.com. If you google "250.122(B) site:mikeholt.com" you will find a number of threads supporting my interpretation above.

Cheers, Wayne

 

[MikeD]

wwhitney: I respectfully still disagree. I maintain that "increased in size" actually does mean "increased in size from the previous installation".

It makes sense to me that an electrician who did not do an original install, but who is reassured that the original install met code; when asked to do an upgrade due to, say, future increased load beyond the capacity of the original install, simply follows the proportionality calculation specified by 250.122(B) to get the required EGC size when increasing the other conductors' size. It may be that the original EGC is larger than what Table 250.122 would require for some good engineering reason known to the original installer, but not to the upgrading electrician (I'm speculating here), so if the upgrading electrician just used the table the new EGC could be inadequately small. I guess the upgrading electrician should also make sure that the calculated EGC size is at least as large as what Table 250.122 would require, in case a math error was made or the original EGC was, in fact, too small.

All of this makes much more sense if we are not talking about a cable (which we probably are for the OP), but the situation of individual wires run in some conduit. One would normally assume that a cable in a non-specialized situation (like we have here) has a code-compliant, adequately sized EGC -- even if the cable is over-sized for future expansion.

A couple search posts I found "at random" concerning Article 250.122(B), although not completely clear, IMHO have the above understanding of "increased in size".

Although the beginning of the "NEC 2011 Handbook" (disseminated by NFPA) reads: "The commentary and supplementary materials in this handbook are not a part of the NFPA Document and do not constitute Formal Interpretations of the NFPA (which can be obtained only through requests processed by the responsible technical committees in accordance with the published procedures of the NFPA).", the authors do have a close connection to the NFPA and try to be as accurate as possible -- not always easy, I expect. Nevertheless, did you find the book's comments I quoted from not conclusive enough? (I can quote more if it might be useful.)

I don't have access (aka a subscription) to all the documents on the http://www.nfpa.org" onclick="window.open(this.href);return false; website that probably would clear up this uncertainty one way or the other.

 

[QueenBee]

wwhitney: I respectfully still disagree. I maintain that "increased in size" actually does mean "increased in size from the previous installation".

It makes sense to me that an electrician who did not do an original install, but who is reassured that the original install met code; when asked to do an upgrade due to, say, future increased load beyond the capacity of the original install, simply follows the proportionality calculation specified by 250.122(B) to get the required EGC size when increasing the other conductors' size. It may be that the original EGC is larger than what Table 250.122 would require for some good engineering reason known to the original installer, but not to the upgrading electrician (I'm speculating here), so if the upgrading electrician just used the table the new EGC could be inadequately small. I guess the upgrading electrician should also make sure that the calculated EGC size is at least as large as what Table 250.122 would require, in case a math error was made or the original EGC was, in fact, too small.

Are you really being serious? You really think this rule only applies when a circuit is being replaced? Are you ignoring the idea that on long runs the resistince will increase hence a reason to increase the size of the wire to begin with and this is why the normally prescribed EGC might not be adequate? If recognize this is an issue than you must disagree that this rule is attempting to solve that issue because otherwise you would realize that this problem is in both new and upgraded circuits and the solution is the same in both.

I have not seen any of your sources that back up this idea, maybe you could reference them?

 

[MikeD]

QueenBee: Yes, I AM serious -- but I may be partially (or completely!) wrong in trying to interpret Article 250.122(B), I am willing to admit. No harm in being wrong, at least I'm trying to uncover its intended meaning, based on the text I'm relying on -- which is mainly from "NEC 2011 Handbook". I'm a little reluctant to quote at length from its commentary passages because of copyright (unlike its NEC passages which, so I have read, because they become law can legally be quoted after that occurs).

I am given the impression that "increased in size" can (at least sometimes) have the definition I suggested based on the "Calculation Example" given where an initial installation (I assume since they wrote "installed" -- past tense) using 250-kcmil copper conductors and a 4 AWG copper EGC has its conductors increased to 350 kcmil (it doesn't say why or when) -- with the "correct code" answer coming from 250.122(B) of 2 AWG copper EGC instead of a Table 250.122 look-up answer of 3 AWG copper.

On the other hand "increased in size" may also have meaning at initial installation time, judging from the following passage: "Where the ungrounded circuit conductors are increased in size to compensate for voltage drop or for any other reason related to proper circuit operation, 250.122(B) requires that the equipment grounding conductors be increased proportionately. Increases in ungrounded circuit conductor size for the purpose of ampacity adjustment, correction, or both are not required to be considered in applying the provisions of 250.122(B).".

Getting back to the OP, my interpretation of the entire text is that using 6/2 AWG on a 40a circuit breaker is NOT a code violation of 250.122(B) -- because it does not apply. Table 250.122 applies instead, since using 6 AWG instead of 8 AWG to provide for possible future EVSE enhancement does not relate to "voltage drop or for any other reason related to proper circuit operation". I do not know if the "NEC 2008 Handbook" (or even earlier editions) have essentially the same explanatory commentary as the 2011 edition. If it does, it is hard for me to see why (even though it doesn't "constitute Formal Interpretations of the NFPA") it wouldn't have been pointed out to the authors as being incorrect -- and corrected in the 2011 edition -- if it were wrong.

Thanks all for engaging in this issue! Any AHJs (electrical inspectors) out there who would like to comment?

 

[Ingineer]

I can't believe you haven't placed MikeD on your foe list (ignore). He is a troll and lives to start arguments, I've never known him to actually help anyone!

Sadly, I have to see his annoying FUD everytime you guys reply to him.

-Phil

 

[MikeD]

Ingineer: I was hoping you might add your $0.02 worth to this discussion. Like the OP I expect there are a number of people who haven't wired an EVSE yet, but due to the often high cost of just "pulling cable" from the circuit breaker box to the garage (or wherever) where the EVSE(s) are to be located, want to anticipate the possibility of a faster future EVSE by using 6/2 cable rather than 8/2 cable (which also actually conserves electricity a little (~.287 ohms less resistance per 1000 feet) due to reduced resistive losses -- not sure what that might translate to in percent less power used for, say, a 100' cable). They would like to be reassured there are no NEC code problems in doing so, if indeed that is the case. So I think it is an issue worth resolving for those people.

Edit update: I calculate that 100' of 8/2 AWG uses about 29W more power than 6/2 when charging at 30a -- is that about right?

 

[QueenBee]

QueenBee: Yes, I AM serious -- but I may be partially (or completely!) wrong in trying to interpret Article 250.122(B), I am willing to admit. No harm in being wrong, at least I'm trying to uncover its intended meaning, based on the text I'm relying on -- which is mainly from "NEC 2011 Handbook". I'm a little reluctant to quote at length from its commentary passages because of copyright (unlike its NEC passages which, so I have read, because they become law can legally be quoted after that occurs).

I am given the impression that "increased in size" can (at least sometimes) have the definition I suggested based on the "Calculation Example" given where an initial installation (I assume since they wrote "installed" -- past tense) using 250-kcmil copper conductors and a 4 AWG copper EGC has its conductors increased to 350 kcmil (it doesn't say why or when) -- with the "correct code" answer coming from 250.122(B) of 2 AWG copper EGC instead of a Table 250.122 look-up answer of 3 AWG copper.

On the other hand "increased in size" may also have meaning at initial installation time, judging from the following passage: "Where the ungrounded circuit conductors are increased in size to compensate for voltage drop or for any other reason related to proper circuit operation, 250.122(B) requires that the equipment grounding conductors be increased proportionately. Increases in ungrounded circuit conductor size for the purpose of ampacity adjustment, correction, or both are not required to be considered in applying the provisions of 250.122(B).".

Getting back to the OP, my interpretation of the entire text is that using 6/2 AWG on a 40a circuit breaker is NOT a code violation of 250.122(B) -- because it does not apply. Table 250.122 applies instead, since using 6 AWG instead of 8 AWG to provide for possible future EVSE enhancement does not relate to "voltage drop or for any other reason related to proper circuit operation". I do not know if the "NEC 2008 Handbook" (or even earlier editions) have essentially the same explanatory commentary as the 2011 edition. If it does, it is hard for me to see why (even though it doesn't "constitute Formal Interpretations of the NFPA") it wouldn't have been pointed out to the authors as being incorrect -- and corrected in the 2011 edition -- if it were wrong.

I think it would be completely absurd to think that 250.122(B) would only apply after the initial installation so I think we can put that to rest as there is no reason to think that and I don't see anything that even hints that would be the case.

I couldn't quickly find the 2008 handbook but the reading I did seemed to be based on 2008 so maybe this commentary clarification is new because this commentary was never brought up. 250.122(B) is the same in both 2008 and 2011. I have no idea why they would not just clarify 250.122(B) instead of leaving it so vague. The commentary definitely makes it clear and while it might not be a formal interpretation clearly if they interpret it this way it's likely that a AHJ would as well and if not initially you should be able to convince them using this.

Fair use will certainly allow me to copy this section from the 2011 NEC Handbook:

The general requirement for selecting the minimum size equipment grounding conductor is to select directly from Table 250.122 based on the rating or setting of the feeder or branch-circuit overcurrent protective device(s). Where the ungrounded circuit conductors are increased in size to compensate for voltage drop or for any other reason related to proper circuit operation, 250.122(B) requires that the equipment grounding conductors be increased proportionately. Increases in ungrounded circuit conductor size for the purpose of ampacity, adjustment, correction, or both are not required to be considered in applying the provisions of 250.122(B). In some cases, use of a conductor with a higher insulation temperature rating allows for compliance with ampacity adjustment and correction requirements without having to increase the circular mil area of the conductor.

Although I don't think 250.122(B) says this I would agree that upgrading the conductor size simply to allow for future expansion should not require a larger EGC because there is no technical reason when its simply to allow for future expansion and the handbook supports this. The OP shouldn't have any problems even if the AHJ realized that 250.122(B) might apply.

 

[MikeD]

QueenBee: I agree with your just previous post. Wwhitney? (and anyone else?)

 

[wwhitney]

Here's my two cents on 250.122(B):

This section is somewhat ambiguous and open to interpretation. What matters in the end is how your AHJ intreprets the text of the NEC. The NEC Handbook is not definitive, it only matters to the extent your AHJ may choose to use it in their interpretation. If your AHJ is flexible, you can land your NM 6/2 on a 40 amp breaker and pass inspection. If your AHJ is a stickler for some reason, they can fail you for it and cite 250.122(B). Since it is ambiguous, they get to interpret it.

Since the original poster asked about being "as code compliant as possible", and to avoid the risk of trouble with a stickler AHJ, I advise against landing NM 6/2 on a 40 amp breaker. If future expansion is your concern, I recommend using a conduit wiring method. This gives you the flexibility to upsize the wiring in the future if you get a bigger EVSE. Or if you want to install larger wiring now, you can upsize the EGC to comply with (a very strict interpretation of) 250.122(B).

Cheers, Wayne

 

[MikeD]

wwhitney: Could a person expect to be able to ask the local electrical inspector's office in advance whether or not they would approve 6/2 cable on a 40a breaker, and make the decision accordingly as to what wiring to use?

 

[wwhitney]

wwhitney: Could a person expect to be able to ask the local electrical inspector's office in advance whether or not they would approve 6/2 cable on a 40a breaker, and make the decision accordingly as to what wiring to use?

Sure, that may be worth a try. If the local electrical inspector is sufficiently knowledgeable and user friendly, you may even get a quick, definitive answer. But your experience may vary, and you may find it easier just to do things a different way that is unambiguously code compliant.

A cautionary note, though. In many jurisdictions, responsibility for code compliance falls on the permit holder, even after plans have been reviewed and a permit issued. If there is an error or code violation on the plans, and the plan reviewer misses it, but the inspector catches it later, the permit holder is still liable for fixing it. So make sure you talk to the right person who can make the final decision on how the jurisdiction interprets NEC as it applies to your situation.

Cheers, Wayne

 

[QueenBee]

If an AHJ tries to increase the EGC wire size on a 6/2 NM-B circuit because you increased the wire size for a 40 amp breaker than you tell him to pack sand and replace the 40 amp breaker with a 60 amp breaker and now the wire size is the standard for a 60 amp breaker (although the NM-B is only rated for 55 amps) and therefore this rule shouldn't apply. Then you ask him how their interpretation has made this installation safer.

The reality is if you just ask the electrical inspector a head of time you are going to get the right answer that 6/2 NM-B on a 40 amp circuit is going to be just fine.

 

[MikeD]

Just to try to "clarify" why a 60a circuit breaker is OK by NEC code for 6/2 copper NM-B wire with rated ampacity (from Article 310.15) of only 55a:
"NEC 2011 Article 240.4 (Protection of Conductors) Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G).
.
.
.
(B) (Overcurrent Devices Rated 800 Amperes or Less.) The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:
(1) The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads.
.
.
."

 

[wwhitney]

If an AHJ tries to increase the EGC wire size on a 6/2 NM-B circuit because you increased the wire size for a 40 amp breaker than you tell him to pack sand and replace the 40 amp breaker with a 60 amp breaker and now the wire size is the standard for a 60 amp breaker (although the NM-B is only rated for 55 amps) and therefore this rule shouldn't apply.

You'd need to use a 50 amp breaker, not a 60 amp breaker, as you can't install a 6-50 receptacle on a 60 amp breaker. That will work out OK unless the EVSE you are installing specifies a 40 amp breaker. I checked one, the Aerovironment EVSE-RS, and its manual does specify a 40 amp breaker. Of course, you could just pull a permit for a 6-50 receptacle and leave the EVSE out of it.

Then you ask him how their interpretation has made this installation safer.

It won't, but it is part of the NEC. Sometimes due to oversight, ambiguity, or corner cases, laws are stupid.

The reality is if you just ask the electrical inspector a head of time you are going to get the right answer that 6/2 NM-B on a 40 amp circuit is going to be just fine.

That may be true 95% of the time, but if you happen to be in the 5%, you need to be aware of this issue.

Cheers, Wayne

 

[MikeD]

wwhitney: Concerning your rebuttal to Queenbee, what is the flaw in my just previous post's reasoning quoting Article 240.4 in which I conclude 6/2 NM-B cable normally can be protected by a 60a breaker?

 

[QueenBee]

The reality is if you just ask the electrical inspector a head of time you are going to get the right answer that 6/2 NM-B on a 40 amp circuit is going to be just fine.

That may be true 95% of the time, but if you happen to be in the 5%, you need to be aware of this issue.

That's my point though, and any intelligent electrical inspector will recognize that applying 250.122(B) to this scenario is not a good idea.

Under the 5% of the time when you get a bad inspector then you put a 60 amp breaker on your 6-50 receptacle, then when they call you out on that, you hardwire it leaving the 60 amp breaker, and when they pull out the manual (I don't think any inspector of mine has ever read the datasheets a head of time or onsite, I would hope the plan reviewers looked things over though) and notice it specifies a 40 amp breaker you install a subpanel next to it with a 40 amp breaker in it and run #8 to the EVSE. Then you ask him how their interpretation has made this installation safer, better, etc.

I guess my point is more so don't live in fear of electrical inspector might pull out some random weird quirk in the electrical code to make your life harder. If what you are doing is better and safer than what might be strictly required you can stand tall knowing that you are on the right side of the issue and are not sacrificing the quality of your installation to meet the needs of 5% of electrical inspectors that are being lame.

Or you could just make your life easier all around and run #8

Now I wonder what the OP ends up doing

 

[wwhitney]

wwhitney: Concerning your rebuttal to Queenbee, what is the flaw in my just previous post's reasoning quoting Article 240.4 in which I conclude 6/2 NM-B cable normally can be protected by a 60a breaker?

There is no flaw in your reasoning. 6/2 NM cable has a base ampacity of 55 amps, and if the load is 55 amps or less, you may protect it with a 60 amp breaker, since 55 amps is not a standard breaker size. My only point was that you can't put a 50 amp receptacle on a 60 amp breaker, if you are wiring your EVSE with a plug.

Cheers, Wayne

 

[wwhitney]

Or you could just make your life easier all around and run #8

Agreed.

Cheers, Wayne

 

[QueenBee]

My only point was that you can't put a 50 amp receptacle on a 60 amp breaker, if you are wiring your EVSE with a plug.

That reminds me of a question I have. Any idea if receptacles are rated for 100% continous load at their rating or just 80%? I realize effectively they can only be used at 80% because of the 125% circuit breaker sizing rule.

 

[MikeD]

Here is a link to a lengthy "How to Size Wire for a Given Load" article by an NEC expert and former(?) electrical inspector that attempts to give some of the reasoning behind NEC rules on this subject: http://www.econline.com/Doc/Hartwell-on-the-Code-How-to-size-wire-for-a-g-0007" onclick="window.open(this.href);return false;

He writes "Twenty years ago selecting wire sizes was comparatively easy for any given load. You took the calculated load, increased it by 125% of its continuous portion, and picked the wire size from Table 310-16 and the overcurrent device from Sec. 240-6. That was essentially all anyone worried about. Today, however, the process is far more complicated. You have to factor in termination restrictions and NEC changes that partially divorce conductor load calculations from overcurrent device sizing requirements."
and
"This is not an easy process. Each time you select a wire size, you will frequently need to consider several principles simultaneously. Speaking as a member of the NEC Committee, every code making panel has to make a decision between a simple rule that is technically incorrect at its margins, and a technically correct rule that is perhaps too complicated. The rules for sizing continuously loaded conductors are perfect examples, being technically correct, and quite complicated.".

Perhaps there are other examples of available articles that some people reading this would like to contribute links to that attempt a similar methodical lay out of the steps involved in making electrical decisions -- anybody?