Wall charger installation at home - suggestions and recommendations? ⚡️⚡️

[Bobthebuilder352]

The round up rule is for sizing the breaker not the wire. If you had a 44A continuous load, you could use 55A wire with a 60A breaker. This install is a 48A continuous load, requiring 60A ampacity for the wire. That's the code.

The wires inside a romex cable, however, are 90C THHN wires. The code requirement to not exceed the 60C ampacity does seem a little arbitrary (though I'm sure it's there for good reason). The romex install will most likely be fine from a safety point of view, but it isn't technically up to code. And I second @ajdelange in wanting to make sure readers who may be pursuing their own installs are aware of the code. If somebody decides to do it anyways fully understanding the decision they're making, that doesn't bother me at all.

Yes, he should flip dip switch 3 to OFF if the wire gets too warm.

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[ajdelange]

The wires inside a romex cable, however, are 90C THHN wires.

I've seen that theory discussed but never verified. Why would anyone in his right mind put a 60° jacket on 90 ° wires ? Why does 6/3 NM-B cost $2.32/ft while 6/3 THHN costs $4.10. I am very skeptical.

The code requirement to not exceed the 60C ampacity does seem a little arbitrary (though I'm sure it's there for good reason).

The NEC is promulgated by the NFPA whose membership includes insurance companies. They are more interested in collecting premiums than paying claims so they ted to take a belt and suspenders approach to safety. I think the good reason you refer to is that someone used 60° wire at more than 55A and a fire resulted.

 

[ajdelange]

Yes, he should flip dip switch 3 to OFF if the wire gets too warm.

No. He should pull out the NM-B and replace it with THHN.
If he flips the dip switch the EVSE will now tell the truck it can only have 40A.

 

[timesinks]

I've seen that theory discussed but never verified. Why would anyone in his right mind put a 60° jacket on 90 ° wire? Why does 6/3 NM-B cost $2.32/ft while 6/3 THHN costs $4.10. I am very skeptical.

It's right in the spec sheet:

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) as specified in the National Electrical Code.

And for further evidence, the next time you strip off the outer jacket of some NM-B, take a peek at the markings on the inner wires. (This may vary by manufacturer because I swear I've taken cables apart before and found markings, but it seems like that is more likely the exception and not the rule.)

 

[Gshenderson]

It isn't whether you consider it broken or not. The problem is that the NFPA does. They think NM-B's ampacity is 55 A and you have installed it on a 60A circuit thus violating NEC. The risk to you is that in case of a fire (a fire from any cause) your insurance company, upon discovering the NEC violation, may refuse you coverage. Unlikely? Well we hope so but if you are willing to accept that risk then it isn't broken.

My reasons for bringing this up again are two. First, I wanted to make sure that you were aware (saw the previous post) that this installation is in violation. Second, I want to make sure that other readers are aware that No. 6 NM-B (Romex) should NOT be used on a 60A circuit.

Understood and I’m fully aware. I’ve seen quite a few EVSE’s wired this way on 60 amp circuits that were done by licensed electricians and passed permit inspection. I’m not in a high heat environment and the run is less than 10’ in oversized conduit. The probability of overheating this circuit to the point of failure due to the wire choice is as close to zero as it can get. But I appreciate your concern and insights.

 

[SANZC02]

I've seen that theory discussed but never verified. Why would anyone in his right mind put a 60° jacket on 90 ° wire? Why does 6/3 NM-B cost $2.32/ft while 6/3 THHN costs $4.10. I am very skeptical.
.

My understanding is it is derated to 55 amps because the wires do not have enough free air for cooling.

The individual wires inside are also not marked so code will not allow you to just strip the outer jacket and run through conduit.

 

[ajdelange]

It's right in the spec sheet:

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) as specified in the National Electrical Code.

[Edit] The following paragraph is not correct. See # 55 below.

What those words say is that you can use NM-B, rated at 60°C at 75 or 80°C (up to 90°C) as long as you follow the NEC rules for derating at the higher temperature. They do not say it is 90° rated wire. Again, use common sense.

Why does 90° rated cable cost twice as much as 60° cable?.

And for further evidence, the next time you strip off the outer jacket of some NM-B, take a peek at the markings on the inner wires.

Can't. There aren't any.

I've learned over many years that if a rumor can't pass the smell test it generally isn't true.

 

[timesinks]

What those words say is that you can use NM-B, rated at 60°C at 75 or 80°C (up to 90°C) as long as you follow the NEC rules for derating at the higher temperature. They do not say it is 90° rated wire. Again, use common sense. Why does 90° rated cable cost twice as much as 60° cable?.

First and foremost, because the code specifies as such. NEC 2020, Article 334 (Nonmetallic-Sheathed Cable: Types NM and NMC), Section 112 (Insulation):

The insulated power conductors shall be one of the types listed in Table 310.4(A) that are suitable for branch-circuit wiring or one that is identified for use in these cables. Conductor insulation shall be rated at 90°C (194°F).

So sure, it may not necessarily be THHN, though it must carry the same dry temperature rating of 90°C, which is the crux of this discussion. My speculation for why they use THHN specifically is they're already manufacturing it. The costs of running a separate line to make a slightly different component when you're already building a component that meets the specifications are probably not worth it.

And you see this in the spec sheets, calling out the use of 90°C wire but saying it must be installed according to the 60°C column. This is exactly what the code says too.

Can't. There aren't any.

Sorry for my error, you're absolutely right on that point. I swear I've taken cables apart before and seen inner markings, but neither scrap of romex I had in my garage just now has them. Clearly I was misremembering my prior experience.

I've learned over many years that if a rumor can't pass the smell test it generally isn't true.

I feel like I've provided ample evidence with product spec sheets and now the actual code citations. If you still think it's just a "rumor" that the inner wire insulation is rated to 90°C, I'm not sure I'm going to be able to convince you otherwise.

 

[timesinks]

They do not say it is 90° rated wire. Again, use common sense. Why does 90° rated cable cost twice as much as 60° cable?.

Thinking specifically about your point about cost difference... We (laymen) as well as electricians and inspectors commonly refer to THHN, but in reality what we're usually buying and installing is multi-rated wire that is THHN, THWN, THWN-2, plus an assortment of other abbreviations. The most notable point here for residential installs is THWN-2 is rated 90°C wet whereas plain old THHN is only suitable for dry locations (and THWN without the -2 is only rated 75°C when installed in wet locations).

This post on the Mike Holt forum (electricians and others in that industry geeking out over technical code stuff) is from somebody who contacted Southwire and asked. They were told that Southwire uses wire "listed as THHN only" in their Romex cables (with the additional caveat that it's not listed to take apart and use as THHN for other purposes and is intended for use only in the assembled cable). THHN is rated for 90°C dry and is not suitable for use in wet locations. It's still 90°C wire for the purposes of an indoor (garage) installation. But that limitation (not being multi-rated as THWN-2 + others) could help explain the cost delta between buying Romex vs "THHN" a la carte.

 

[ajdelange]

So sure, it may not necessarily be THHN, though it must carry the same dry temperature rating of 90°C, which is the crux of this discussion.

If you still think it's just a "rumor" that the inner wire insulation is rated to 90°C, I'm not sure I'm going to be able to convince you otherwise.

I'm not sure I'm convinced of anything yet but I'll tell you what I think and I think we're pretty much in agreement though you certainly had me confused there for a bit.

I found rhis in the SIMpull Spec

"Conductor insulation is 90°C-rated polyvinyl chloride (PVC), nylon jacketed.*

This would be in accordance with Art. 334.112 and sounds like the description of THHN for sure but there are 21 90° rated cable types listed in Table 310.4(A) that satisfy the requirement of Art, 314.112.

I also found this in the Spec...

"...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) as specified in the National Electrical Code"

...and, probably puzzled by the ramblings in the Mike Holt forums was confused as to what it meant though once the light came on it is clear enough (I think). The relevant article is 334.80 which says, in my interpretation, that you can use 90° ratings to do derating calculations as long as, when all is said and done, you do not push more than the ampacity of a 60° rated conductor through the wire. and, according to Table 310.16A that's 55A. The fact that NB-B is not listed in the 60° column header in that table bothered me for quite a while but then I realized that that doesn't matter and that this is THE 60° rating for No. 6 copper wire period. Yesterday I had myself convinced that I hadn't a clue as to what the ampacity of #6 NM-B is (though Ugly's says 55A) but today I am convinced Ugly's is right.

Bottom line: It is my opinion that using NM-B on a 60A circuit is a code violation even though the individual conductors have 90° insulation (of that I am convinced but I am not convinced, as many of the forums say, that they are THHN or any other particular type).

Also part of the bottom line: The more I know the more I know I don't know. This exercise has been a good reminder of that.

 

[ajdelange]

This post on the Mike Holt forum

That quote says that the wires are "listed" as THHN only". I doubt they are "listed" as THHN as you cannot take them out of the jacket and use them in an appliction that requires THHN. I think the spec for Southwire's Romex says what they are:

"Copper conductors are annealed (soft) copper. Stranded
conductors are compressed stranded. Conductor insulation is 90°C-rated polyvinyl
chloride (PVC), nylon jacketed."

These conductors might indeed have been pulled off the company's THHN production line but they aren't THHN. Sounds silly but it is what it is.

 

[TheIglu]

I really do appreciate deep dive discussions like this.

Now where is a good place to buy 6/3 MC for reasonable money?

 

[ajdelange]

I’ve seen quite a few EVSE’s wired this way on 60 amp circuits that were done by licensed electricians and passed permit inspection.

Should the unthinkable happen the owners of those EVSE can sue the electrician.

 

[timesinks]

Bottom line: It is my opinion that using NM-B on a 60A circuit is a code violation even though the individual conductors have 90° insulation (of that I am convinced but I am not convinced, as many of the forums say, that they are THHN or any other particular type).

Then we've found common ground

 

[psklenar]

I'm having my charger installed by the same electricians who installed my standby generator, transfer switch and load shedder a year & a half ago. ...

Actually, they are here as I type this and they found a way to fish the cable from the utility room to the garage (40' away) thru the basement's finished ceiling without having to cut any drywall (other than the small hole punched thru to the garage) or running conduit outside as I had expected!

Successfully and cleanly installed (with about 45' of 4 gauge in case those discussing wire are curious)! Now I just need my truck.

pat----

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