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I am adding a cable to connect Tesla Gen-3 Wall Connector to a NEMA 14-50 outlet using a NEMA 14-50 plug.

NEMA 14-50 outlet supplies four wires - Neutral, Ground and two Hots. Tesla Wall Connector, on the other hand, needs only three wires - Ground and two Hots.

Is it allowed to leave the Neutral pin open inside the NEMA 14-50 plug (see the diagram below)? If it is not allowed or not desirable, what should I do about it?

Wiring Diagram

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    It is allowed, but from what I have read on here, if using current code, an outlet requires it to be GFCI protected. If the charger is hard wired it does not need GFCI. Most EV chargers have better GFCI protection, but new code says the outlet must have GFCI. If the outlet has been there for years, it might be grandfathered in.
    – crip659
    Jun 16 at 16:52

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That is fine. Just because the 14-50 socket offers both hots and neutral doesn't mean the appliance needs to take it.

Now, let's do a few health checks on this circuit. On a NEMA 14-50 the breaker must be 50A or 40A and the wires must be at least large enough for that ampacity. The Wall Connector can go as high as 60A (or 80A?) but the NEMA 14-50 socket and plug cannot. So the Wall Connector must be commissioned to <= breaker trip.

The cord must be actual appliance cord, and not Romex. It needs 3 wires (no requirement for 4th wire). The white is used as a hot, do not connect it to neutral. Must be 6 AWG for 50A or 8 AWG for 40A.

The EVSE already has a "Smart GFCI" onboard. This GFCI is able to self-reset itself a number of times (the fault often clears, so this is worth doing), and if it fails utterly, it can message your phone to warn you that you have a problem. This satisfies the January 2023 GFCI requirement for a hardwired EVSE but does nothing for a plug-in EVSE.

If your state has adopted NEC 2020, you have two choices: #1 hard-wire the EVSE, replacing the socket with a disconnect switch. #2 install a Stupid GFCI breaker ($100). The Stupid GFCI will trip at the same time as the Smart GFCI, doing a hard power cut, breaking the EVSE's retry and notice abilities, and you will get a surprise in the morning.

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  • Thank you very much for the extended answer. My outlet is on a non-GFC 40A breaker, so I am planning to commission the wall connector at 32A. Realistically, I can't do much more, because my service is a 100A, and the quote for upgrading it to 200A was prohibitively expensive (>$8,000). The rest of the appliances draw ~30A when turned on together, so adding Tesla at 48A, or even at 40A, would put me too close to the 80% limit. Jun 16 at 18:44
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    @Sergey yup, that's exactly the right thing to do re: provisioning. There is tech starting to emerge that will allow you to go higher by pre-empting other appliances. (it's available now in "the Span" at the $8000 price point, not a coincidence, but will drop like a stone soon. Eaton and Square D are working on it, and Eaton will support Siemens and GE panels.) Just watch the NEC 2020 GFCI gotcha. Hardwired is no big deal if you have to. Jun 16 at 18:49
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Yes, you can do that. But far better is to hardwire the Tesla device. That does a few things:

  • One less point of failure (no plug to get loose, etc.)
  • Removes the GFCI requirement. (This may or may not be a requirement in your area, but it is being phased in as states adopt newer versions of NEC code.)

IMHO, there really is little reason to use a plug/cord for any appliance that is permanently attached to the structure - disposal, dishwasher, oven, EV charger, etc. In some cases local code (or manufacturer instructions) may require it, but otherwise hardwire makes sense. That is not the case for washers, dryers, refrigerators, etc. as they are designed to be moved for maintenance and other reasons.

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  • Another reason to add a plug instead of hard-writing is the need to charge vehicles from different manufacturers in a garage that is wired for a single 50A circuit. My other EV will be a Volvo (coming this fall), and my sister's EV is a Chevy. The other two cars come with chargers with a NEMA 14-50 plug, so I decided to wire my wall charger via a plug as well. Jun 16 at 18:08
  • The problem is, 14-50 (and similar) are not designed for frequent plugging/unplugging. For your Volvo (assuming you keep the Tesla) best is to hardwire it as well. For visitors (Chevy) I don't have a great answer. The long-term fix will be a standardized charging station/cable/etc. for all manufacturers. We're not quite there yet. Jun 16 at 18:23
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    @SergeyKalinichenko Based on some articles it should work with other cars as well...
    – vidarlo
    Jun 16 at 18:31
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    @vidarlo My wall connector is a Gen3; the one in the article is a modified Gen2, which is no longer available :-( Jun 16 at 18:50

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