Laundry list of proposed changes to the 2017 NEC

[hcdavis3]

The National Electrical Code (NFPA 70) is a "model" code. States are welcome to adopt whatever they want. Both your state (Massachusetts) and mine (Oregon) have adopted the 2017 NEC (which is where this requirement was added), but with amendments.

Massachusetts Electrical Code

Here is your states amendments:

https://www.mass.gov/files/documents/2017/12/14/2017.pdf

I don't see any amendments in section 625, so I presume 625.54 is in force. This is a prime example of how many AHJ's (Authorities Having Jurisdiction) are unaware of this requirement (perhaps to your benefit).

It is squirreled away in the EV charging section, not in the "general" sections that would apply to everything like an RV plug.

It really chaps me that they sought to add it for EV charging but not for RV connections. It is not like folks don't plug in RV's at RV parks *every* day and often in the rain... Presumably they can more easily get away with requiring this really expensive breaker because they assume people with EV's have lots of money. To require it for RV parks would be extremely expensive and likely not politically tenable.

I would love to see some actual injury statistics on this... Is it an issue that actually needed solving?

View attachment 402022
View attachment 402023

Awesome man. Thanks very much.

 

[doghousePVD]

Boy, I'm just a complete layman, but I wish that any plug that ends in -50 be capable of 50 peak and 40 continuous amps. That I now have knowledge that, while engaging a code-approved outlet, I could plug in a 14-50 plug and draw well over the rated amperage terrifies me.

You should not be terrified. If you draw 50 amps on a 40 amp breaker, it will trip. So what? The current Tesla portable chargers only draw 32 amps anyway.

Tripping is annoying, but certainly not terrifying. Reset the breaker, and lower the charging rate in the car.

 

[F14Scott]

As I understand it, breakers trip from heat, like the kind of heat that would set a wall on fire.

Murphy's law of technology is that a $400 TV will blow to protect a $.10 fuse. Thus, I want the breaker to be the last resort, not the nominal.

 

[woodguyatl]

Dang I might be in violation then. I installed it two years ago and have yet to get a permit and have it inspected. I was going to do some other electrical work and get it covered under the same permit. I’m just a horrible procrastinator. I don’t do much without a sense of urgency. I’ll look into seeing what a GFCI breaker would cost.

Just because it is code doesn’t mean it is a good idea. At this point let it ride. It is very unlikely an inspector will both know the code and notice yours is not GFCI protected unless they are specifically asked to inspect it and, if they are like inspectors here in Atlanta, they will still get it wrong.

 

[WilliamG]

Yeah, in case you are interested, here is the math behind this:

Table 310.15(B)(16) tells us that 8 AWG Copper wire is good for 40 amps at a 60c insulation rating. If you are allowed to use the 90c insulation rating (which I think all NM cable and THHN/THWN sold today is good to 90c) then it is good for 55 amps.

Since 334.80 limits us to using the 60c rating for overall capacity, you can't do over a 40a circuit, HOWEVER, you are still able to use the 90c rating for temperature derating and derating due to many conductors in a conduit.

So assuming your using NM cable and it does not run through the same holes in studs as other wires (in some situations you may have to derate for that), or assuming you are using THHN/THWN in conduit and you don't have more than three "current carrying conductors", then we don't need to derate for any of that. I am also assuming the run is not like super long and that we might want to derate for voltage drop due to distance (though this is NOT a requirement - only a recommendation).

Then basically we get to use that entire 15 amp delta between the 40 amp cap on the rating due to the 60c limitation and the actual 90c insulation rating, as potential for temperature derating.

So looking at table 310.15(B)(2)(a) for 90c rated copper, we can have an ambient temperature of 131 degrees Fahrenheit and only have to use a derating of 0.76. So that times 55 equals 41.8 amps. The next step up goes to 140 degrees, but it is a 0.71 multiplier which is only 39.05 amps.

Your solution is absolutely safe and I applaud the abundance of caution. Though I probably would have stuck with the 14-50 since it is code compliant. I then might have set the car down to 24 amps to add that extra margin of safety. That way you have the full 32 amps easily available if you need to charge faster once in a while. ;-)

Bump for an interesting thread. I have a question which is a tad off topic, but still related to EV charging and thus would be relevant for the Tesla mobile charger, too.

If you have a 40A breaker, a Siemens 30A L2 charger (Versicharge) for a 2019 VW eGolf, is #10/3 NM-B acceptable or not? I’ve got one electrician telling me yes it’s fine, and another telling me it’s not fine and that it should be #8 for this circuit.

Here’s the manual for the L2 charger:

https://images.homedepot-static.com/catalog/pdfImages/c2/c2bc7b8f-0ac5-4476-8d78-d221c7f47349.pdf

Just trying to get clarification here. A good explanation would go a long way to resolving this. Thanks, guys.

 

[Sophias_dad]

Bump for an interesting thread. I have a question which is a tad off topic, but still related to EV charging and thus would be relevant for the Tesla mobile charger, too.

If you have a 40A breaker, a Siemens 30A L2 charger (Versicharge) for a 2019 VW eGolf, is #10/3 NM-B acceptable or not? I’ve got one electrician telling me yes it’s fine, and another telling me it’s not fine and that it should be #8 for this circuit.

Here’s the manual for the L2 charger:

https://images.homedepot-static.com/catalog/pdfImages/c2/c2bc7b8f-0ac5-4476-8d78-d221c7f47349.pdf

Just trying to get clarification here. A good explanation would go a long way to resolving this. Thanks, guys.

That's a hard NO, for at least two reasons....

page 7 of the manual says "Use 6-8 AWG, 75C copper wire to connect to supply circuit" (ya, nm-b is supposed to only use the 60c rating, but I'll give that a pass)...

EV loads are considered continuous because they are expected to run for more than three hours. As a result, you are required to oversize the breaker AND the wire by 25%, so rather than planning for a 30 amp load, you should really be planning for a 37.5 amp load. I guess that 10AWG would 'work' if you were planning to use the 90C rating(THHN in conduit et. al), but the versicharge manual says 6-8. The cost to put all that 10AWG in conduit would most likely be greater than to just use the right #8 in NM-B. You don't say how long the run is, so maybe my numbers are off. If its a longer run, I'd even consider going to 6AWG just for the efficiency increase.

Another thing to consider for installation... with 6-2 and 8-3 NMB(and bigger) you can avoid drilling holes in all your joists and just go direct, stapling the wire to the (usually bottom) edge of the joist instead. This might make your wire run shorter, or installation easier, although you could argue that drilling a hole and threading wire through it might be easier than nailing on a floor joist overhead. You really only need a staple every 3-4 joists though, so at that point stapling becomes faster/easier.

 

[WilliamG]

That's a hard NO, for at least two reasons....

page 7 of the manual says "Use 6-8 AWG, 75C copper wire to connect to supply circuit" (ya, nm-b is supposed to only use the 60c rating, but I'll give that a pass)...

EV loads are considered continuous because they are expected to run for more than three hours. As a result, you are required to oversize the breaker AND the wire by 25%, so rather than planning for a 30 amp load, you should really be planning for a 37.5 amp load. I guess that 10AWG would 'work' if you were planning to use the 90C rating(THHN in conduit et. al), but the versicharge manual says 6-8. The cost to put all that 10AWG in conduit would most likely be greater than to just use the right #8 in NM-B. You don't say how long the run is, so maybe my numbers are off. If its a longer run, I'd even consider going to 6AWG just for the efficiency increase.

Another thing to consider for installation... with 6-2 and 8-3 NMB(and bigger) you can avoid drilling holes in all your joists and just go direct, stapling the wire to the (usually bottom) edge of the joist instead. This might make your wire run shorter, or installation easier, although you could argue that drilling a hole and threading wire through it might be easier than nailing on a floor joist overhead. You really only need a staple every 3-4 joists though, so at that point stapling becomes faster/easier.

Thank you for the reply. I guess I’m confused even further! NM-B is only supposed to use the 60C rating? The electrician who is doing it insists it’s fine because it’s 90C rated. The #10/3 wiring currently that was put in is just going through holes drilled in the joists of an old garage with no drywall ceiling. There’s no conduit, - just the wire in its jacket or whatever that is called. It’s around a 15-foot run.

Here are some of the things he said to me via text:

“I heard that you believe that the ampacity of the circuit breaker exceeds the allowable current (expressed in Amps) for the wire. Now usually this would be true given the breaker is rated for 40 degrees Celsius and the conductor was rated at 90 degrees Celsius which would put you in a 75-degree column under THHN which is the conductor type of the NMB. However if you look at code reference to 240.4(B) it clearly states the exception for the rule. That would be if the ampacity (the FLA [FULL LOAD AMPERES] on the equipment nameplate) rating of the equipment does not exceed that of the rated conductor then you are allowed up to 600% overcurrent protection because of startup ampacity which ranges anywhere from 200%-400% for approximately .05 seconds which concludes as to why they allow you to do this. The FLA on the given equipment is 30amps. Also based on 27 years of experience I will guarantee that if you put an amp meter on the phase it will never go to 30 except on start up. Typically it'll probably run at approximately 70 to 75% of the name plate rating in the worst conditions. OR I can call up a Seattle DPD electrical inspection and let them tell you exactly what I just did. Homeowners and DYI'ers tend to get a sense that they know something that really they do not. I'm a WA ST Master Electrician and I would hope that I knew what I was talking about.”

I told him about the manual saying 6-8 AWG and having spoken to a different electrician. He replied:

“Your electrician doesn't know the code well enough then. The FLA on the charger is 30amps at 100% there is a selector switch that can operate it at 25% values ranging from 25% to 100%. It doesn't matter if the breaker or the overcurrent protection is upsized on a piece of dedicated equipment with the ampacity not rated higher than the full and ampacity of the conductors.”

And then:

“If #10 isn't rated for a continuous 30 amp load then I'm going to retire in the electrical field and become a plumber. Basically what I'm trying to tell you is is they come up with these formulas based on the most extreme usage you can imagine. With that being said, number 10 can handle that 30 amp load all day all night forever and if I'm not mistaken# 10 can handle up to a hundred amps. The actual ampacities are based on the insulation of the said conductor. You should have read the manual that I got with the charger.”

So there you go. Not sure what to even say anymore.

 

[Sophias_dad]

So there you go. Not sure what to even say anymore.

Say goodbye to the electrician, and report him to whatever authority you can....

NM-B is only allowed to carry 30A....... even at the 90C rating it can only go to 40A. He's gonna get someone killed with statements like 100A.

Ampacity Charts - Cerrowire

NM-B can only be used at the 60C rating......have him look at 334.80 of the NEC

https://www.mysouthwire.com/medias/...duct-specifications/h77/hfc/8854083698718.pdf

"Southwire® Romex ® Brand SIMpull® NM-B (nonmetallic-sheathed) cable may be used for both exposed and concealed work in normally dry locations at temperatures not to exceed 90°C (with ampacity limited to that for 60°C conductors)"

His FLA statements are crap. He's might be thinking you are installing a motor'ed item, but an EV charger takes full load all the time(after the first minute ramping up).

Worse than his FLA statements, he doesn't know about the 25% upsizing...

https://www.pge.com/includes/docs/pdfs/about/environment/pge/electricvehicles/ev5pt3.pdf

https://www.ecmweb.com/national-electrical-code/code-basics/article/20897937/ev-charging-systems

"Because these loads are continuous, it follows that overcurrent protection for supplying electric vehicle supply equipment must have a rating of not less than 125% of the maximum load of the electric vehicle supply equipment [625.21]. For that same reason, the conductors must also be sized no less than 125% of the continuous loads based on the terminal temperature rating ampacities, as listed in Table 310.15(B)(16), before any ampacity adjustment [110.14(C)(1) and 210.19(A)(1)]."

Call him on his DPD inspection, do it for him. He could and should have his license suspended. He probably should get some retraining. He's relying on what he remembers from what he learned 27 years ago, and at the rate he's going, he's gonna start burning houses down.

He is correct that on motor'ed items, its sometimes okay to put a bigger-than-conductor-ampacity breaker on, usually done to avoid startup current induced trips. EV's are not remotely like that.

 

[WilliamG]

Say goodbye to the electrician, and report him to whatever authority you can....

NM-B is only allowed to carry 30A....... even at the 90C rating it can only go to 40A. He's gonna get someone killed with statements like 100A.

Ampacity Charts - Cerrowire

NM-B can only be used at the 60C rating......have him look at 334.80 of the NEC

https://www.mysouthwire.com/medias/...duct-specifications/h77/hfc/8854083698718.pdf

"Southwire® Romex ® Brand SIMpull® NM-B (nonmetallic-sheathed) cable may be used for both exposed and concealed work in normally dry locations at temperatures not to exceed 90°C (with ampacity limited to that for 60°C conductors)"

His FLA statements are crap. He's might be thinking you are installing a motor'ed item, but an EV charger takes full load all the time(after the first minute ramping up).

Worse than his FLA statements, he doesn't know about the 25% upsizing...

https://www.pge.com/includes/docs/pdfs/about/environment/pge/electricvehicles/ev5pt3.pdf

https://www.ecmweb.com/national-electrical-code/code-basics/article/20897937/ev-charging-systems

"Because these loads are continuous, it follows that overcurrent protection for supplying electric vehicle supply equipment must have a rating of not less than 125% of the maximum load of the electric vehicle supply equipment [625.21]. For that same reason, the conductors must also be sized no less than 125% of the continuous loads based on the terminal temperature rating ampacities, as listed in Table 310.15(B)(16), before any ampacity adjustment [110.14(C)(1) and 210.19(A)(1)]."

Call him on his DPD inspection, do it for him. He could and should have his license suspended. He probably should get some retraining. He's relying on what he remembers from what he learned 27 years ago, and at the rate he's going, he's gonna start burning houses down.

He is correct that on motor'ed items, its sometimes okay to put a bigger-than-conductor-ampacity breaker on, usually done to avoid startup current induced trips. EV's are not remotely like that.

Thank you for that. My electrician who installed my Tesla charger was saying very similar things, so I’ll convey this information and hopefully it’ll help. I’m not an expert in this field, neither have I claimed to be, so the more info out there the better!

 

[GPinzone]

What if you get a 14-50 outlet for a welder instead of an EV? Will that pass inspection?

 

[Sophias_dad]

What if you get a 14-50 outlet for a welder instead of an EV? Will that pass inspection?

Need a little more data.... if that 14-50 is connected to a 40 amp breaker with 10 gauge NM-B wire, then no. 10 AWG NMB will only carry 30 amps(continuous or not). If it were 8 gauge, yes its allowed, but is likely to cause nuisance trips if used with an EV at more than 32 amps or so..... it might get to 40 even, if the breaker is in a nice cool basement and the nearby breakers aren't heavily used.

'Inspection' is also a bit of a loose term. I imagine there are some inspectors who are sticklers, and some who let things slide to some degree.

 

[Runt8]

Need a little more data.... if that 14-50 is connected to a 40 amp breaker with 10 gauge NM-B wire, then no. 10 AWG NMB will only carry 30 amps(continuous or not). If it were 8 gauge, yes its allowed, but is likely to cause nuisance trips if used with an EV at more than 32 amps or so..... it might get to 40 even, if the breaker is in a nice cool basement and the nearby breakers aren't heavily used.

'Inspection' is also a bit of a loose term. I imagine there are some inspectors who are sticklers, and some who let things slide to some degree.

Wouldn’t it be against code to install a 40 amp breaker on wire sized for 30 amps?

 

[Feathermerchan]

Yup.

 

[Sophias_dad]

Wouldn’t it be against code to install a 40 amp breaker on wire sized for 30 amps?

Yes and no.... if the thing you are trying to drive is a well known big motored and hardwired device, it is sometimes expected(and even required) to install an unexpectedly large circuit breaker to cover the startup current. The installation manual should be very specific about the wire ampacity and circuit breaker expectations if the device in this category. The usual case for this in a residential setting is the compressor of an air conditioner.

I don't think this is allowed on circuits with outlets at all, even a single-outlet dedicated circuit.