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Question: When installing a 50 amp receptacle on a 30 amp circuit, where it's the only receptacle on that circuit, is there any requirement to add a "max amperage" sticker or label, or anything else that needs to be done to identify at the plug that the circuit is not rated for 50 amps?

Per NEC 2017: 210.21(B)(1) - "a single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit."

50>30 so a 50 amp receptacle on a 30 amp circuit complies, and the requirements for receptacle ratings relative to circuit ratings (I.e. 210.21(B)(2) and (3) and 210.23) only apply when two or more receptacles are on the branch, so I don't see anything in the (national) code that would disallow this type of installation (local codes notwithstanding).

I would probably just label the outlet regardless, since my concern is really for when I sell the home, I could see the future home owner trying to use the 50 amp receptacle for a higher power appliance and would then experience nuisance tripping. But I was curious if there was any requirement for this per the NEC.

I didn't see anything in the receptacles section, but thought there might be something in another section that someone more familiar with the code might know.

Background: I just bought an electric car and I'm looking to install a level 2 EVSE. The unit I want is only available as a plug-in option (no direct wire option) and comes with either a NEMA 14-50 or a NEMA 6-50 plug. The unit has internal dip switches for setting the max current draw so you can install it on circuits that are less than 50 amps.

I have a few existing 10-30 receptacles in the workshop next to the garage that aren't used so I was going to convert one of these to the newer plug style (have done research on how to do this and feel pretty comfortable about adding a proper ground to do this).

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  • What make and model is the EVSE you're looking at? Jul 31, 2021 at 13:53
  • Grizzl-e, classic.
    – CBRF23
    Jul 31, 2021 at 13:53
  • Also should note, the existinf 10-30 receptacles are each on their own circuit. So just one receptacle on the circuit.
    – CBRF23
    Jul 31, 2021 at 13:54
  • Where is the breaker box located relative to the receptacles, and what wiring method is used for these existing circuits? (NM cable? armored/metal clad cable? wires in conduit of some sort?) Jul 31, 2021 at 13:59
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    Here, have a link to the user manual Jul 31, 2021 at 15:23

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You could do this...

You could do as you describe with installing a NEMA 14-50 or 6-50 on a dedicated 30A circuit, as the requirement for dedicated branch circuits is simply that the receptacle rating be not less than the branch circuit rating, as per NEC 210.21(B)(1) (exceptions omitted for clarity):

(1) Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

You could replace the stock cord with a 30A cord/plug, or just use an A/C whip kit to hardwire it

The Grizzl-E supports hardwiring, as per the user manual, so you could theoretically replace the cord with a 30A cord/plug. You'd need to use a cord suitable for a standard cord gland, though, which rules out normal (flat, type SRD) dryer cords.

However, you could use a type SRDT cord with a NEMA 14-30 or NEMA 6-30 plug, along with a matching 30A receptacle, and setting the DIP switches on your charger to 24A. Obviously, you could also hardwire it using an A/C whip kit and a suitable faceplate (½" KO faceplates are fairly standard items) on the receptacle box, for that matter.

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  • Thanks threephaseeel - this is really helpful for my planning. I upvoted, but I haven't marked it as the answer since my original question was really about installing a 50 amp receptacle on a 30 amp circuit, and I could see someone in another situation (i.e. an RV owner or something) searching for that answer and this wouldn't be the answer for them. Maybe I should edit my original question for more clarity...
    – CBRF23
    Jul 31, 2021 at 19:58

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