L 14-50 EV receptacle

[gene6]

It's a regulatory difference, not a physics difference. So for identical installs with #8 Cu on a 50A breaker and a 75C rated receptacle, one THWN-2 and one NM, while the latter install is an NEC violation, it's no more likely to burn up at the receptacle in the manner under discussion.

Now if the receptacle is marked for 60C terminations only, that means that the thermal design was relying there being a #6 Cu conductor, so using #8 certainly could contribute to the problems depicted.

Cheers, Wayne

Say you have two EV chargers and two identical EV's. If I have 100' of #8 NM cable going across a attic on then down to one EV charger and also a run of 3/4 EMT with #8 THHN right next to the NM for the other one why then is the NM cable limited to 40 amps and the THHN in conduit have a ampacity of 50? I am no engineer but I'd imagine the THHN in conduit can dissipate more heat than wires in a NM cable.
Before LED lighting i'd see the same thing with incandescent lighting, you'd open up a heavily used light fixture and the conductors from NM cable would crumble to dust where actual THHN would not.
I'd be surprised to learn the plastic insulation used in NM cable is the same quality as THHN.

 

[don_resqcapt19]

While not saying this is the case with EVs, I have seen a number of molded plug ends where it appears the heat was generated at the point of connection between the cord and the plug blades within the molded end, and that heat also damaged the receptacle

 

[wwhitney]

Say you have two EV chargers and two identical EV's. If I have 100' of #8 NM cable going across a attic on then down to one EV charger and also a run of 3/4 EMT with #8 THHN right next to the NM for the other one why then is the NM cable limited to 40 amps and the THHN in conduit have a ampacity of 50?

For non-technical reasons only, e.g. bias against NM cable. UL Standard 719 for NM cable gives two options in section 4.4 for the insulation; to paraphrase loosely 4.4(a) says "same as THHN but no labeling" and (b) says "something else that performs the same."

I am no engineer but I'd imagine the THHN in conduit can dissipate more heat than wires in a NM cable.

Well, the main difference is the metal conduit in the first case, vs the overall plastic jacket in the second case. Not sure which would be a larger impediment to heat dissipation, but neither of them presents an impediment greater than what the NEC already accounts for.

Cheers, Wayne

 

[LarryFine]

I'd be surprised to learn the plastic insulation used in NM cable is the same quality as THHN.

There's a huge difference between NM from 50-60 years ago and that of today.

 

[g-and-h_electric]

I am going throw in my 2 cents......

Wasnt the 14-50, originally designed as a "range" receptacle? If so, ranges arent generally unplugged very often, nor used at full capacity for long periods ( over say 4 hours) frequently. If an EVSE is used with one and plugged and unplugged regularly, I think we are potentially seeing the receptacle contacts loosening from this. (Havent we all seen loose receptacles of the 5-15 variety the get loose from a lot of use?)

Does anyone know if the manufacturers have done a long term contact tension test? I do agree that the Hubbell Bryant receptacles have a larger contact area, and definitely better lugs.

 

[don_resqcapt19]

Say you have two EV chargers and two identical EV's. If I have 100' of #8 NM cable going across a attic on then down to one EV charger and also a run of 3/4 EMT with #8 THHN right next to the NM for the other one why then is the NM cable limited to 40 amps and the THHN in conduit have a ampacity of 50? I am no engineer but I'd imagine the THHN in conduit can dissipate more heat than wires in a NM cable.
Before LED lighting i'd see the same thing with incandescent lighting, you'd open up a heavily used light fixture and the conductors from NM cable would crumble to dust where actual THHN would not.
I'd be surprised to learn the plastic insulation used in NM cable is the same quality as THHN.

Yet other non-metallic jacketed cables such as SE or TC do not have the 60°C limitation that NM does. I don't think there is actually a real world reason for the limitation of the current on NM...just a listing and code limitation.

 

[infinity]

Yet other non-metallic jacketed cables such as SE or TC do not have the 60°C limitation that NM does. I don't think there is actually a real world reason for the limitation of the current on NM...just a listing and code limitation.

I agree in reality it's all about the same doesn't matter if it's NM, SE, or pipe and wire. If the conductors are all the same size none of those wiring methods will cause the receptacle to overheat.

 

[tortuga]

I'd say pipe and wire provides better cooling from contact with thermal insulation, its common to see bundles of NM cables going thru bored holes, with pipe and wire de-rating would apply over 3CC.

While not saying this is the case with EVs, I have seen a number of molded plug ends where it appears the heat was generated at the point of connection between the cord and the plug blades within the molded end, and that heat also damaged the receptacle

Yeah good point I have wondered about that also, I think there was a post on here about EV plugs with a temp sensor in the cordcap.
Regardless of NM or pipe and wire I'd say its better to hardwire.

 

[BarryO]

Wasnt the 14-50, originally designed as a "range" receptacle? If so, ranges arent generally unplugged very often, nor used at full capacity for long periods ( over say 4 hours) frequently. If an EVSE is used with one and plugged and unplugged regularly, I think we are potentially seeing the receptacle contacts loosening from this. (Havent we all seen loose receptacles of the 5-15 variety the get loose from a lot of use?)

My wife has two 50A cord-and-plug connected kilns in her studio (one ceramic, one glass). She never wanted to use them at the same time, so one branch circuit was sufficient. Just for this issue, I installed a separate receptacle for each. Those contact surfaces aren't very large and I could see them weakening with repeated plugging and unplugging over time. Put in a big A/B switch so that only one receptacle at a time was connected to the branch circuit. The contact surfaces in the switch are several times those in the receptacle.

 

[don_resqcapt19]

View attachment 2574302
I'd say pipe and wire provides better cooling from contact with thermal insulation, its common to see bundles of NM cables going thru bored holes, with pipe and wire de-rating would apply over 3CC.
....

NM requires the same ampacity adjustments as conductors in a raceway where the NM is installed without maintaining spacing, so if you install them touching each other for 24" or more, you have not maintained spacing an you need to apply the ampacity adjustment factors.

 

[gene6]

I was just looking up the specs of a few EV rated 14-50 'range' receptacles;
The Hubble EV receptacle prohibits aluminum wire;

https://hubbellcdn.com/installationmanuals/WIRING_PD1186_INSTALLINST.pdf

Another one called a Journeyman pro also does not allow aluminum wire.
Both are 75C rated.

 

[tortuga]

True, but the 14-50 plug seems commonplace on EVSE's, I suspect because 14-50 receptacles are commonplace (used for large RV's).

I would never plug an RV into an 14-50 'EV charger' receptacle without testing it first, I have seen many wired like this one with no neutral:

I don't think there's any such thing as a NEMA L14-50 (locking) receptacle.

50A locking exists, but is never used for residential ev chargers, I think have seen one on a forklift charger.

 

[letgomywago]

While not saying this is the case with EVs, I have seen a number of molded plug ends where it appears the heat was generated at the point of connection between the cord and the plug blades within the molded end, and that heat also damaged the receptacle

Seen that on 240 ac units in hotels and apartments. Melted RCD cord end.

 

[letgomywago]

I would never plug an RV into an 14-50 'EV charger' receptacle without testing it first, I have seen many wired like this one with no neutral:
View attachment 2574320


50A locking exists, but is never used for residential ev chargers, I think have seen one on a forklift charger.
View attachment 2574319

Lots of times I've seen a customer ask for an RV pedestal like a Midwest style one for EV and RV use.

 

[BarryO]

50A locking exists, but is never used for residential ev chargers, I think have seen one on a forklift charger.
View attachment 2574319

In my copy of NEMA WD 6, this type is marked "This configuration is currently inactive"

 

[darekelec]

Does a 50 amp receptacle installed outdoors have to be marked WR ?

 

[Elect117]

Does a 50 amp receptacle installed outdoors have to be marked WR ?

This could probably be it's own post, but

406.9(B)(2)(a) -
A receptacle installed in a wet location, where the product intended to be plugged into it is not attended while in use, shall have an enclosure that is weatherproof with the attachment plug cap inserted or removed.

Only 15A, 20A, rated 125 and 250V have a WR listing and label.

 

[darekelec]

I saw a pic of Leviton 50A WR receptacle .

 

[hillbilly1]

Has anyone looked into the difference in physical construction of a L14-50 EV receptacle vs a standard one?

Thanks

I just bought one, and it is a lot heavier, and deeper.

 

[hillbilly1]

Just installed the new EV rated plug for a Porsche hybrid, found out a standard range cover will not fit! 70 miles to a place that carries the correct cover. Looks like my hole saw skills will come into play.