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I have a 1940s house with a Nema 10-30 receptacle for the dryer. Halfway from the main panel, this circuit is spliced in a junction box, and in that box, I see there are only 3 wires: 2 hot and one neutral, which is bonded to the (metal) junction box.

I would like to know if this is safe, or how to make it so, for 2 different uses of the 10-30R: first, it is to remain in service for the dryer. Second, if I can make it adequately safe, I would like to use it as a backup EV charger, for those occasional times when I need to charge 2 cars at the same time (my main EV charging will happen on another circuit). Possibilities for EV charging are using Tesla's 10-30 adapter or converting the receptacle to something else. If there is no way to make this safe for EV charging without pulling all new wire, I will keep it as dryer-only, but I would like it to be safe for that use as well. thanks

EDIT: To clarify, there is no sign the junction box is grounded, it is fed from the panel by 3 wires only: hot / hot / neutral (confirmed this is bonded to the neutral bus bar in the panel)

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    It's not safe as is. Grandfathered, yes; safe, nope! If the wiring has a proper neutral, you can retrofit a ground wire. There's a reason this was finally banned in the 1996 code cycle, and it was long overdue for the ban. So leaving it as is for the dryer - not safe. But grandfathered...
    – Ecnerwal
    Mar 1 at 17:31
  • How about a photo of that junction box? Mar 1 at 23:20
  • The part in question can't be photographed -- opening the box cover, the red and black wires are wirenutted together just fine. The white wires run outside the box and are just barely visible through a tiny gap in a neighboring closet. The way the white wires are attached to the outside of the junction box is obviously wrong so even if connecting neutral to the box was correct, I would be changing it to bond it properly. It looks like I will be moving the white wires inside of the box and not connecting them to the box, then running a separate ground to replace the 10-30 with a 14-30.
    – Byofuel
    Mar 2 at 0:28

3 Answers 3

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It isn't safe to use a 3-wire dryer connection.

It's grandfathered, meaning it was legal when installed (maybe!) and they don't make you update your house every code cycle. That is not the same as safe - if it was, code would not change!

However, you can't extend it in any way. You want to add a ground to that box, that's an extension and you can't use neutral for that, no. Neutral is not ground in any way whatsoever. That was the whole point of outlawing the practice in 1965 for most things and 1996 for dryers and ranges. The box needs to remain floating.

A warning about /2+ground cable for dryers and ranges. It was never legal to use /2+ground cable for a dryer circuit. The general idea in 1965 was that the types of cables legal for a groundless range/dryer connections (/3 no ground, #10 SEU) were going extinct, and so the problem would cure itself when stocks depleted. Nobody ever imagined people would get creative and use /2+ground cable, abusing the ground as a neutral, something Code never allowed. That would be insane, since dryers are entirely 120V machines except for the heating element, for commonality with gas variants, so the neutral carries real, live, no-joke neutral current. And a bare ground is not up to that task.

You can retrofit a ground, though.

You can run a separate ground wire to ground the box, per the rules in 250.130(C). #10 wire via any route to a junction box with #10 or larger ground going back to the panel.

This has an effect on the landscape. Presuming your dryer cable was legacy legal (so not 10/2+gnd), you now have a fully qualified 4-wire feed, same as if you wired it with /3+gnd. You can use it in the normal ways, including an extension to an EV outlet.

EV charging is not to be underestimated

for those occasional times when I need to charge 2 cars at the same time (my main EV charging will happen on another circuit).

Wait, what now????

On a 1940s house? EV charging is the harshest load a house will ever see, and you can't just keep dogpiling more and more load onto an old service. That will have consequences.

You need to start at the NEC 220.82 service load calculation. Note that dryers factor into that calculation as a 40% load, but EV circuits come in as a 100% load, treated more harshly than even HVAC.

Now if the numbers work, great… but if they don't work, we have options. As you know, EV stations can be adjusted to any charge rate, and what's more, they can adjust on the fly - either to coordinate 2 vehicles sharing a limited power allocation, or to follow the surplus power available right now in the panel.

With a Power Sharing strategy, you live within the Load Calculation, and split the power to 2 cars with two charge stations (EVSE is the proper term, they're not actually chargers). They dynamically share it among both cars; when one car finishes or is absent, the other gets the full amount. This is sort of like a valet showing up at 3 AM to unplug one car and plug on the other, without you having to do anything.

With an EVEMS / Load Management strategy, the station monitors what other loads in the house are using in real time, and sends the surplus to the car. This disregards the Load Calculation entirely, which means, it also disregards amp limits and you can charge as fast as you want, up to the limit of the service. You can have a 60A charging station on a 60A service, even. So with EVEMS, you solve the 2-car problem by charging at the Fastest Charge Possible and then moving the charge cord before you go to bed.

Cost isn't extreme, it typically adds $300 to the cost of a wall unit, but you have to choose a wall unit that supports it, such as Tesla, Wallbox or Emporia.

They don't really have stations that double-stack both EVEMS and also Power Sharing in the North American market, yet. Wallbox has it in Europe.

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    Thanks for the details. The wires to the 10-30 are correct - 3 insulated: black, red, white. So I will add a bare copper #10 ground back to the panel, switch it to a 14-30, and then it will be available for occasional 2nd car charge. The service was upgraded around the '60s so I have 100A - still not ideal for EVSE but better than original '40s. A separate project is to investigate upgrading to 200A -- there are incentives to do this in my locale, but the process takes months, so I must live with 100A for the time being. A new 60A circuit will charge the 1st EV, with set limits for now.
    – Byofuel
    Mar 2 at 3:09
  • Lol another great answer!
    – Fattie
    Mar 2 at 14:08
  • @byofuel I stand by my advice re: load calculation, good luck. Mar 4 at 4:35
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While 10-30s are allowed to be grandfather for use, they were ban in 96 because they cause deaths.

Very highly recommended to change to 14-30.

If the box is grounded back to the panel, with the neutral bonded, you also have the chance of having current on a non current carrying wire. A bad unsafe hack for a broken neutral.

You have two unsafe connections on one circuit.

Edit. With the box not grounded, to the edit in question, that box has the same danger as a dryer on a 10-30 circuit. You can get a shock from the box.

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  • Thanks, the junction box shows no sign of being grounded (and it is fed by 3 wires - hot / hot / neutral). To change to a 14-30, is there any way to add a ground other than running new wire from the panel?
    – Byofuel
    Mar 1 at 21:15
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    @Byofuel Newer code allows you to run a separate ground wire not in a cable. Only a ground wire can do this, not a neutral or hot wire. I would disconnect the neutral bonded to the box and connect both neutrals together with a wire nut/wago(lever connector). Not quite sure if you can just go to the closest grounded box(receptacle/light) or need a 10 gauge or larger ground connection.
    – crip659
    Mar 1 at 21:23
  • Thanks, it appears this post may answer the question of how to run a separate ground for the 14-30: diy.stackexchange.com/questions/237064/… Since my only other receptacles in this area are 20A (12 gauge) it seems I will be buying 50' of bare 10 gauge copper and running it back to the panel.
    – Byofuel
    Mar 2 at 1:13
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I would like to know if this is safe, or how to make it so

No it is not safe, a 10-30 does not provide a ground and the ground connection in the junction box is not meant to support sustained current over it.

Replace the socket with a NEMA 6-30 using a proper ground and keep the (fake) neutral disconnected. OR Run a proper neutral through to the panel and replace with a 14-30.

The more versatile option is the 14-30 because for some reason Tesla doesn't deign to sell the safer 6-30 adaptor and instead sells a 10-30. (Third party sellers do carry it)

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  • They sell 10-30 and 14-30 because people have old (10-30) or new (14-30) dryer receptacles available. Hardly anyone has a 6-30 in residential use, so no point in them selling one. Mar 1 at 17:27
  • You wrote "the ground connection in the junction box is not meant to support sustained current over it" -- I should note that there is no sign the junction box is grounded, it is fed only by 3 wires: hot / hot / neutral. I'm not sure what you mean by "fake" neutral -- from what I've read these older dryer receps didn't require ground, so this is a real neutral (I confirmed it's bonded to the neutral bus bar).
    – Byofuel
    Mar 1 at 21:23
  • @Byofuel A fake neutral is when some unknowing people connect neutral to a ground wire to fix a broken neutral wire, neutral is also known as a grounded conductor. Neutral is expected to carry current, ground is just to keep you safe when oops happen.
    – crip659
    Mar 1 at 22:04
  • Ok, and since the junction box is (probably) not grounded, it's not exactly a fake neutral as just a messed up junction.
    – Byofuel
    Mar 2 at 0:18
  • I think switching to 14-30 with a separately run 10 gauge bare ground is emerging as the best solution, but how do I power the dryer -- replace its 10-30 cord & plug with a 14-30 or get a 10-30 to 14-30 adapter?
    – Byofuel
    Mar 2 at 1:28

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