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I am installing an outdoor receptacle (NEMA 14-50) on a dedicated circuit for EV charging. While the charger uses a 14-50 plug, it only draws 24A (80% continuous rating for 30A circuit).

I have two questions about installing this receptacle:

  1. Can I install this on a 30A breaker? My expected load is always going to be 24A, even if the receptacle can handle up to 50A.
  2. To provide Stage 1 EV charging (for overnight charging), can I install a 20A receptacle on the same circuit? Again, the expected load is always 12A (80% of 15A).
  • What make and model is this wacko EV charger that only pulls 24A but insists on a 50A plug? I'd chop the plug and replace it with a 14-30 if I were in your shoes (or better yet, take the whole dang cord off the thing and replace it with a standard-issue 4-wire dryer cord) – ThreePhaseEel Feb 22 '17 at 4:34
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    The NEMA 14-50 is actually very common for EV charging, regardless of actual charging current. At work, we have those installed, so I'd like that plug to allow charging at work, so having the same receptacle at home is sort of essential, otherwise I'd need multiple (expensive) EVSEs. They make them with NEMA L6-30/50 and NEMA 6-50 too, but they're less common. – Hari Ganti Feb 22 '17 at 7:19
  • @ThreePhaseEel you need to get out of the 1990s and join the modern world! That said, the OP is confusing the max current setpoint on his EV with the design capability of a NEMA14 receptacle. – Carl Witthoft Feb 22 '17 at 19:14
  • All the same, adapter connectors for EV charging cables are not terrible expensive. Even the Tesla ones (the Tesla cable itself is pricy). Better to install a 30-amp receptacle and keep the adapter handy. – Carl Witthoft Feb 22 '17 at 19:16
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    @CarlWitthoft I understand how the NEMA plug/receptacle specification works, and that a NEMA 14-50R is a 50A-rated receptacle, but as with appliances that have 5-20P plugs on them, they don't all draw 20A (or 16A). The EVSE is intentionally limited because they can charge more (EDIT: No pun intended) for a 40A continuous model. Having an adapter circumvents a problem that doesn't exist. I'll just install a 50A circuit to the 14-50R receptacle. Simple enough. – Hari Ganti Feb 22 '17 at 19:20
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Hard "no". The only receptacle you can install on a 30A circuit is a 30A receptacle. NEC 210.21B3.

enter image description here

You mentioned the EV industry's tendency to put 14-50 on every charger. That creates a real mess. You cannot install a 50A receptacle unless you have 50A wire and breaker. As you note in the above table, there's an exception where it's also allowed on 40A circuits, but the reason for the exception is there's no such thing as a 40A receptacle, and that exception is bullseyed at the special case of range/ovens. For a new -50 in a garage, where anything could be plugged into it from a better EV supply to a welder, best to use 50A cable so people get exactly what is on the tin.

Contemplating a situation where replacing the 10AWG cable is not practicable... I would get a "generator transfer switch" that takes the form of a small subpanel with an interlock so two specific 240V breakers can't be on at once, and takes readily available breakers (because I'd change them). Normally, those panels backfeed; I'd not. The 30A supply would go to its buses. I'd change one breaker to a 30A and feed the 14-30. The other to 20A and feed the 20A receptacle.

enter image description here

If forced to plug into 30A service, I would use a 30A receptacle and a cheater cable. This is not quite legal, but since it's not part of the building, it's out-of-scope for the permitting and inspection process. I'd specifically aim to make it as obvious as possible that it is a cheater cable -- to warn "the next guy" that this is not 50A as advertised. A receptacle installed in a building should always be what it looks like. I shudder to think of people solving this problem with a neat 14-50 installation onto 10AWG wire; later they sell the house to a guy motivated by that sweet 50A service in the garage.

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    See my comment on the main post about why the NEMA 14-50. It's mostly as a standard for EVSE receptacles since charging current is limited by the vehicle. As such, a 50A EVSE couldn't charge my car any faster than a 30A. If it weren't standardized to anything (and it's not truly standardized anyway), you'd have a hard time plugging in wherever you go. – Hari Ganti Feb 22 '17 at 7:22
  • Your suggestion is interesting, but I'd rather just run two separate circuits for the purpose. 1) 50A @ 240V (NEMA 14-50) and 2) 20A @ 120V (NEMA 5-20) – Hari Ganti Feb 22 '17 at 7:24
  • Your eagerness to follow code is laudable, and I'm glad you are able to do that. For many, rewiring is impractical or above their comfort level, and they make do with an extant 10AWG run formerly for dryer or water heater. – Harper Feb 22 '17 at 15:47
  • Couldn't agree more. Mismatching a receptacle to a circuit is dangerous for the next guy. For the amount of money you are saving it's not worth the risk. – mreff555 Feb 22 '17 at 16:24
  • But unless something else goes really wrong, the "next guy" will try to pull 40+ amps and the breaker will pop. One would hope he's smart enough not to put in a 50A breaker without examining the output wire size :-) – Carl Witthoft Feb 22 '17 at 19:18
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First: I'm not a licensed electrician. However, the 2017 NEC seems clear to me.

tl;dr: I'd say for question 1) "yes" and for 2) "no" - rationale follows.

While table 210.21(B)(3) lists specific receptacle ratings for specific circuit ratings, that is explicitly for multiple outlets per circuit. For a single receptacle on a circuit, 210.21(B)(1) says "a single receptacle installed in an individual branch circuit shall have an ampere rating not less than that of the branch circuit." enter image description here

So I think the answer to 1) is yes, you can put a 50A receptacle on a 30A circuit, as long as it's the only receptacle on the circuit. For 2) it's no, for two reasons. First, now you have 2 receptacles on the branch circuit, so 210.21(B)(3) applies, and prohibits it. (This makes sense; a 30A breaker doesn't protect a 20A receptacle). Second, code only permits a single outlet on an EVSE circuit:enter image description here

  • Hello, and welcome to Home Improvement. Good answer: keep 'em coming! – Daniel Griscom Jan 19 at 15:16

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