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Edit: Never mind. I found a 24 amp charger with a 10-30 plug for only slightly more $ than the 14-40 charger I was planning on getting, so I'm going to leave the outlet as-is.

I turned of the 30A breaker and used my non-contact voltage tester to make sure these wasn't any voltage at the outlet. When I pulled the cover plate off the NEMA 10-30 dryer outlet in my garage (built in 1994) in preparation for replacing it with a NEMA 14-50 outlet so I can plug in a EV charger (drawing 24 Amps), I was happy to see that there were 4 wires coming into the box. I was surprised, however, to see that the bare copper (ground) wire was connected to the neutral terminal of the outlet, while the white (neutral?) wire was not connected to anything. While the dryer has been working fine for 30 years, from what I've read, that is not up to code, even prior to 1996. Since that seems wrong, I'm concerned what else could be screwed up (specifically is the white wire really the neutral), and want to test things before I install the NEMA 1450 outlet.

With the breaker still off, I verified that there is continuity between the bare copper wire and a nearby water pipe (for the washing machine), so I think that means it is a good ground wire, but I don't know how to test that the white wire is a good neutral.

My question are:

  1. Am I correct that the existing wiring connection the ground wire to the outlets neutral connection is not up to code?
  2. Is testing continuity between the bare copper wire and a nearby water pipe a correct way to test that it is a good ground wire?
  3. How can I test that the white wire is a good neutral?
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  • Is there a reason you want your charger to be plug-in vs hardwired?
    – ThreePhaseEel
    Commented Mar 11 at 2:09
  • 3
    I'm expecting to move in the near future, so I don't want to invest in installing a hardwired charger at this location.
    – New EV Owner
    Commented Mar 11 at 2:13
  • 2
    Not using a hardwired unit requires using a GFCI breaker. Using a hardwired unit, the EVSE does the GFCI, (which saves a bunch of money) and when you move out, you turn off the breaker, remove it, and put a blank cover over the box. As already noted in one answer, you can't put a 14-50 on a 30A circuit, and you can't bump up the breaker size to suit if the wire is not oversized for 30A (which is highly unusual.)
    – Ecnerwal
    Commented Mar 11 at 15:55
  • 1
    @Ecnerwal Yes and no. Assuming the existing receptacle (wrong as it is) predates the 240V GFCI requirements, a replacement back to the 14-30 that it probably was previously based on 4 wires inside the receptacle box is arguably a repair of the existing circuit and not a new circuit and therefore not subject to the GFCI requirement. But an "upgrade" to 14-50 receptacle means new cable and is really a new circuit with the GFCI requirement.
    – manassehkatz-Moving 2 Codidact
    Commented Mar 11 at 23:55
  • 2
    Worth a read on sizing: diy.stackexchange.com/q/277803/55930
    – Machavity
    Commented Mar 12 at 12:59

4 Answers 4

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STOP!

Based on more comments that "an electrician said". DO NOT HIRE THAT ELECTRICIAN! You can't install a 14-50 receptacle on a 30A circuit. Period. Full. Stop. You either put in a 40A or 50A circuit (both are OK with a 14-50) or you put in a modern 30A 14-30 receptacle. And then you get an appropriate plug/cord to match. Tesla has those cords/plugs readily available for their mobile chargers. Other brands might or might not. Or switch to hardwired. BUT YOU CAN'T USE 14-50 RECEPTACLE WITH A 30A CIRCUIT!.

  • You can't put a 14-50 receptacle on a 30A circuit. A 14-50 can only be on a 40A or 50A circuit. The only way you can do that is you replace the circuit breaker with a 40A or 50A breaker and replace the cable because it is 99.99999% guaranteed that the existing cable is only 10 AWG.

  • 10-30 is long obsolete. Your setup is a typical "don't know what we're doing swap between a good 14-30 and a bad 10-30 because we got a dryer with a 3-wire cord".

The right thing to do here is:

  • Replace the 10-30 receptacle with a properly wired 14-30 receptacle.
  • If you are planning to still use the dryer, replace the 3-wire cord and 10-30 plug with a 4-wire cord and 14-30 plug and remove the neutral/ground bond from the dryer.

Depending on the type of EVSE (a.k.a., "charger") that you have, you may want to seriously consider hardwiring instead of a receptacle.

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  • I'm actually replacing the 10-30 outlet with a 14-50 outlet based on the recommendation of a licensed electrician. I expressed the concern of someone (not me) plugging in a 50 amp applance, and he said he would just use a permanent marker to prominently mark the cover plate 30 amps. All the plugin EV charging cables I've found, even those that draw 24 amps or less, have a 14-50 plug. Would it be better to install a 10-30 outlet and use a 14-50 to 14-30 convert to plug in the charger?
    – New EV Owner
    Commented Mar 11 at 20:29
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    A THOUSAND TIMES NO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    – manassehkatz-Moving 2 Codidact
    Commented Mar 11 at 20:38
  • 4
    @NewEVOwner fire that electrician and get a different one who isn't flamingly clueless about the NEC
    – ThreePhaseEel
    Commented Mar 12 at 1:41
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Am I correct that the existing wiring connection the ground wire to the outlets neutral connection is not up to code?

Not to code. You are correct.

Is testing continuity between the bare copper wire and a nearby water pipe a correct way to test that it is a good ground wire?

No. All current applied to a good ground wire should go to ground. Continuity testing with a grounded wire is at best unreliable.

How can I test that the white wire is a good neutral?

A simple voltage test between hot and neutral is typical.

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2
  • Just to correct the record, I have now talked to three licensed electricians, and everyone of them said having the 2 hot wires and a ground connected to a 3 wire 240 outlet (10-30) and leaving the white (neutral) wire unconnected is code (at least it was in 1994).
    – New EV Owner
    Commented Mar 17 at 4:53
  • @NewEVOwner Even if that were true, your dryer isn't a 240 load. It's not allowed to run without a neutral wire.
    – Robert Chapin
    Commented Mar 17 at 14:19
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Check for continuity from the neutral wire to ground, you should get continuity since ground and neutral are connected at service entrance.

then disconnect the neutral wire at the panel and test again. The continuity should go away. If it doesn't you have a dodgy cross connection between neutral and ground or you have not identified the correct neutral wire.

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2
  • If the wire you expected to be neutral was actually hot, wouldn't this put 240V across your multimeter? Probably you should start with it in AC-volts mode, on a range large enough to handle 240 Vrms. Only if you find the voltage is near 0V should you switch it over to continuity / resistance mode.
    – Peter Cordes
    Commented Mar 12 at 17:33
  • Yeah, you should turn the power off and check for dead before doing anything else.
    – Peter Green
    Commented Mar 12 at 19:54
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The best way to test continuity of the white would be to test line voltage wires to the white, then disconnect the white in the panel and re-test hoping that no voltage is measured.

Using a 14-50r on a 30A circuit has been debated several times here on SE, but there is no arbitor to end discussion. The NEC has two separate paragraphs, where the wording is distinctly different:

210.21(B) Receptacles. (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.

(3) Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall not be less than the values listed in Table 210.21(B)(3), or, where rated higher than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.

To me it seems a 50A receptacle is not less than 30A, but my interpretation is without authority, the Code says:

90.4 Enforcement.(B) Interpretations.The authority having jurisdiction for enforcement of the Code has the responsibility for making interpretations of the rules, for deciding on the approval of equipment and materials, and for granting the special permission contemplated in a number of the rules.

You could call you local Electrical Inspector, most have published office hours at beginning of shift.

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3
  • Look at Table 210.21(B)(3) which you listed. It isn't just "not less", it shows exactly which receptacle sizes are permitted on each circuit size.
    – manassehkatz-Moving 2 Codidact
    Commented Mar 12 at 0:16
  • The Table is titled Ratings for Circuits Serving More Than One Receptacle, and is not referenced in 210.21(B)(1).
    – NoSparksPlease
    Commented Mar 12 at 0:24
  • Well you're right that's More Than One Receptacle. So back one receptacle: 210.22 Permissible Loads, Individual Branch Circuits - An individual branch circuit shall be permitted to supply any load for which it is rated, but in no case shall the load exceed the branch-circuit ampere rating. Hypothetically if you put a 14-50 on a 30A circuit, how in the world would you make sure the load doesn't exceed 30A? Friend comes over with their own mobile charger with 14-50, the presumption is that any place it can plug in can provide 40A peak, 32A continuous, which is not allowed on a 30A circuit.
    – manassehkatz-Moving 2 Codidact
    Commented Mar 12 at 0:28

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