Don't use a $5 range outlet for EV charging • Hacker News Board

Re: Don't use a $5 range outlet for EV charging

#31

Post by Kirby64 » Sat, Jul 13, 2024, 2:49 PM UTC

quickthrowman wrote: post #30

Kirby64 wrote: post #29

Earlier quoted context omitted.

I can assure you this often has nothing to do with torque. The Leviton outlet lists a torque of 40 inch pounds. You can hand tighten much tighter than that relatively easy with a reasonable screw driver. There’s some instances of undertorqued outlets, sure, but that isn’t the predominant factor here. The crap outlets are the issue.

True, you can easily hand tighten to 40 inch pounds. After looking at some more evidence, I agree that it’s probably just a poorly designed receptacle, probably on par with a residential 5-15R which are made to a much lower standard than a comparable commercial 5-15R. It looks like Leviton may have discontinued the receptacle that lots of people had melt on them so that probably is the case.

The 279 outlet is just replaced by the 279-s00. I don’t think there’s much meaningful difference for Leviton outlets. It’s just similar to residential vs commercial ad you state.

Re: Don't use a $5 range outlet for EV charging

#32

Post by egberts1 » Sun, Jul 14, 2024, 7:05 PM UTC

quickthrowman wrote: post #28

Kirby64 wrote: post #15

Earlier quoted context omitted.

What's your math on this? I don't understand how you're getting to 37A. A 50 amp rated outlet (backed by a 50 amp rated breaker, and wire capable of handling 50 amps) is fully NEC compliant if you run it for 40 amps continuously (80% derating) or 50 amps temporarily (which NEC defines as a load expected to continue for 3 hours or more). EV chargers fall under the 80% derating. I'm not aware of any EV charger that use…

> What's your math on this? I don't understand how you're getting to 37A You have to derate conductors installed in ambient temperatures greater than 86F. I would definitely use NM-B 6/2G (or 6/2G MC cable) for a NEMA 14-50R in a garage, just to account for derating since you get to start at 75A for #6 rated for 90C. The first derating factor is .94 for ambient temps between 87-95F, .94 times 40A is 37.6A if you use…

Thanks! The further clarification and use of terminology is much needed here. Plus I needed that citation!

Re: Don't use a $5 range outlet for EV charging

#33

Post by egberts1 » Sun, Jul 14, 2024, 7:13 PM UTC

Kirby64 wrote: post #19

egberts1 wrote: post #17

Earlier quoted context omitted.

I did take liberty here in saying 37A-ish (40A is code) because that's what some national fire marshalls are reporting about hot garage and reuse of range-type wiring for new purpose of EV charging. It's the wire material and size issue in hot area.

But, if it supports 40A charging it'll charge at 40 amps unless you back off the charging rate (which nobody does, typically). You'd always assume 40 amps for circuit purposes.

See @quickthrowman's comment for detailed breakdown on high-temperature and copper wire.

Re: Don't use a $5 range outlet for EV charging

#34

Post by Kirby64 » Sun, Jul 14, 2024, 7:37 PM UTC

quickthrowman wrote: post #28

Kirby64 wrote: post #15

Earlier quoted context omitted.

What's your math on this? I don't understand how you're getting to 37A. A 50 amp rated outlet (backed by a 50 amp rated breaker, and wire capable of handling 50 amps) is fully NEC compliant if you run it for 40 amps continuously (80% derating) or 50 amps temporarily (which NEC defines as a load expected to continue for 3 hours or more). EV chargers fall under the 80% derating. I'm not aware of any EV charger that use…

> What's your math on this? I don't understand how you're getting to 37A You have to derate conductors installed in ambient temperatures greater than 86F. I would definitely use NM-B 6/2G (or 6/2G MC cable) for a NEMA 14-50R in a garage, just to account for derating since you get to start at 75A for #6 rated for 90C. The first derating factor is .94 for ambient temps between 87-95F, .94 times 40A is 37.6A if you use…

I’m not disputing that you have to derate conductors based on excess temperature according to NEC. I’m saying that no EVSE exists that will pull 37A. It’ll pull either 32A or 40A and needs wiring and a breaker backing it that either is 40 or 50 amp rated, respectively.

Also, Romex (NM-B) is always considered to be 60C rated, and you cannot assume 90C rated conductors (in the case of a properly rated 90C conductor like THHN) because the outlet and breaker must also be matched and capable of 90C. No 40-50A breaker I’m aware of is 90C rated. They’re typically 75C, and sometimes 60. Likewise, no NEMA 14-50 outlet I’ve ever seen is 90C rated. They’re all 75 or 60C. The crappy Leviton one mentioned in the article is 60C. That means everything is essentially treated as 60C for derating purposes besides derating factors for things like bundled conductors.

In comparison, Bryant and Hubbell outlets (the more expensive ones EV forums tend to recommend) are 75C rated, so you can usually use the 75C derating tables for everything, since breakers are THHN are typically capable of 75C. MC cable would also be 75C rated, as well.

Re: Don't use a $5 range outlet for EV charging

#35

Post by Kirby64 » Mon, Jul 15, 2024, 9:47 PM UTC

quickthrowman wrote: post #25

CaliforniaKarl wrote: post #13

> Even though the 14-50R outlet is technically a 50A outlet, when used as a kitchen range plug, they are often wired on a 40A circuit. This is permitted by the Canadian Electrical Code rule 26-744 5). I wonder if the US National Electric Code allows this.

Yes, but only for circuits with multiple outlets, an individual branch circuit must use a wiring device not less than the ampacity of the branch circuit. You are allowed to use 40A and 50A receptacles on a multi-outlet 40A circuit. You’re also allowed to use 15A and 20A receptacles on a multi-outlet 20A circuit. Table 210.21(B)(3) of the NEC https://up.codes/s/outlet-devices

You have it backwards. If you have a single receptacle on a branch circuit then the OCPD (breaker) must be sized at or under the receptacle. I.e., a 50 amp outlet can be backed with a 50 amp breaker or anything smaller. You could even have a 20 amp breaker (and 12 gauge wire) backing a 50 amp outlet, which is common for welding applications where peak currents are extremely high on arc start but continously are much lower. There's a specific carve out for welders as well, but it applies to any outlet.