5

I'd like to change the obsolete unsafe NEMA 10-30R to NEMA 14-30R so that I can safely have a smart splitter switch for dryer and EV charging.

Behind the NEMA 10-30R I see 3 wires: black, white (taped with black tape), bare. On the panel I see 4 wires: black, red, white, bare. See attached photos.

Any idea what's going on? Previous owners moved the laundry from inside the house to the other side of the wall in the garage. So my guess is they converted the old outlet to a junction box which unfortunately I don't have access to since they have built cabinets where the laundry used to be.

Is the NEMA 10-30R currently wired with hot hot ground instead of neutral? How can I test with a multimeter whether it's neutral or ground? Maybe check for continuity between the wires in the outlet and the panel? Or can I check for continuity between this outlet's "neutral" and an adjacent 15A outlet ground? If it's ground instead of neutral, does it mean it's safe to also use it for EV charging?

NEMA 10-30R panel

8
  • 2
    Dryers usually need neutral, so that ground will be not in code being used as neutral. Life might be easy if you can extend the red enough inside of the box/panel, if not will need extra work replacing cable/removing cabinets. Cannot have a box behind cabinets, unless they have an open back or are removable by hand only(pull out).
    – crip659
    Commented May 24, 2023 at 10:35
  • 1
    Can you post a photo that clearly shows where the cable/wiring enters the outlet box please? Commented May 24, 2023 at 11:42
  • 6
    Junction boxes need to be accessible, so go find that or else run a whole new set of wiring/cable and cut off and abandon the run that goes to a buried box. There is continuity between neutral and ground anyway in a properly wired system, so that test won't tell you anything.
    – Ecnerwal
    Commented May 24, 2023 at 12:48
  • Is this the only panel in the house or is there another one? I think it is a subpanel based on a bunch of things, but looking again, it looks like bare neutral (allowed in service entrance wiring) and no ground, which would imply main panel. There may be more issues here... Commented May 24, 2023 at 20:02
  • 1
    Aha! So then this the practical main in that all circuits except solar and a few large breakers (e.g., HVAC) are here. And the feed is 100A. Which means your main is probably fine (probably 200A) but you really need a load calculation on this subpanel. And realistically, this subpanel could do with replacement with a 42-ish space panel. Commented May 24, 2023 at 21:34

2 Answers 2

12

The hidden junction box is the key. Junction boxes are supposed to always be accessible, and this is one of the reasons why. But you have multiple issues here.

A dryer requires neutral. EVSE (a.k.a., "car charger") does not require neutral. Both currently require ground. But dryers used to not require ground. A dryer without ground (i.e., a proper 3-wire dryer circuit) can be grandfathered. But you don't have a proper 3-wire dryer circuit, and it can't be grandfathered anyway.

A proper 3-wire dryer circuit has hot, hot and neutral. A bare wire, with certain exceptions that absolutely do not apply here, is ground and not neutral. So you have a ground wire being used as neutral. That's strike one. It isn't to code and it isn't safe. That's separate from "combining neutral and ground" isn't safe - the bare wire, never designed to be neutral, ratchets up the "not safe" to another level.

In addition, even if this were OK as far as ground vs. neutral, this could not be grandfathered. Why? The dryer circuit is a proper 4-wire circuit, as you see in the breaker panel. Which means that either the improper 3-wire circuit used to go someplace else and was rerouted through the hidden junction box to a new circuit in the panel (the rerouting negating the grandfather clause) or it was originally in the hidden junction box location as a 4-wire circuit and was extended to a 3-wire circuit in a new location, which is a brand new circuit extension, so grandfathering never had a chance to apply. Either way, a 3-wire receptacle/circuit is simply not allowed for a dryer in your house. Period. That's strike two.

But wait, there's more! Do you see the difference between the 40A breaker and the 30A breakers? The 40A breaker is a double breaker. The 30A breaker is actually two single 30A breakers connected with a handle tie. A double breaker provides common shutoff (turn off one "half" for service and the both halves are guaranteed off) and common trip (if one side trips, both halves are guaranteed off). A handle tie provides common shutoff but does not provide common trip. For a lot of things that makes no difference. But for a dryer that uses neutral, it makes a huge difference. Essentially the heating element uses the two hots and the motor uses one hot + neutral. If the motor overloaded while the dryer was heating, it is possible to have the hot that feeds the motor trip and not the second hot. That would leave the dryer appearing to be dead (no controls lights or heating) but would still leave one hot wire live. That's strike three. A proper 30A double breaker doesn't cost very much - in fact normally very little, if anything, more than 2 single 30A breakers.

The interesting thing is that, assuming there are no other issues and the wire is sized correctly, 10 AWG, but even that I wouldn't assume without verification, this circuit can be used by dedicating it to EVSE. EVSE normally does not require neutral. It does require ground. But even that requires access to the hidden junction box to make sure (and fix it wrong) that the bare wire from this cable connects to ground only and not to neutral. Neutral in that hidden box would then be capped for future use. But if you do that, you will need an entirely new circuit for the dryer. If you simply extend from the hidden box to the current dryer location with a proper /3 cable (black hot/red hot, white neutral/bare ground) and install a 4-wire 14-30 receptacle then you can use it as planned.

But step 1 absolutely must be to access the hidden junction box. Depending on the type of cabinet (especially the material used for the back, which could be anything from 1/4" cardboard to 1" solid wood) and how precisely you know the location of the box, your options are:

  • Move the cabinet. Measure and mark a hole in the cabinet for access. Move the cabinet back.
  • Measure based on expected location. Cut some small exploratory holes until you find the junction box. Cut an access hole.
  • Abandon the existing wires altogether and run a new /3 cable from the breaker panel to the dryer location.

There are a couple of other big considerations. This panel is full. It may be possible to add more half-size breakers. It is also possible, based on the other problems, that the panel is already more than full. The only way to tell is to check the instructions, which is usually on a label inside the panel door.

You may also have total load issues. Sharing the EVSE and dryer avoids making thing worse. But it is quite possible that either this panel or the main panel (I am assuming this is not the main panel based on lack of a main breaker, among other things) is oversubscribed. Not number of breakers (well, maybe that too...) but total power used. The way to do that is with a load calculation, which adds up various fixed loads, standard factors based on the size of the house, etc. and tells you how much power you need to provision to feed that panel properly. With so many half-size breakers, I am a bit concerned that a lot has been added without considering the feed to this subpanel or possibly even the utility feed to the main panel.

Based on a comment, this subpanel is the effective main panel for the house - i.e., almost every circuit comes from this panel, which is fed by a 100A breaker in a meter main that also houses solar, surge protector, HVAC, etc. Based on that, my real recommendation is:

  • Add a new subpanel. I recommend a large panel (at least 30 spaces) and a main panel (just remove the neutral/ground bond and a ground bar if needed) can make a lot of sense due to the way these things are priced. Feed it with a 100A-ish (90A may make sense, depending on wire costs) breaker from the main panel, connected with appropriate aluminum wires or cable.
  • Add a 30A double-breaker to the new subpanel for the dryer. Run /3 cable (hot/hot/neutral/ground) to the dryer location and install a NEMA 14-30 receptacle. Replace the dryer cord/plug with NEMA 14-30 and remove the dryer neutral/ground bond. You may need to put in a GFCI breaker, depending on local NEC version and local modifications. If so, that's the way it is. You can't grandfather the old stuff anyway.
  • Add a 30A double-breaker to the new subpanel for the EVSE. Run /2 cable (hot/hot/ground) to the EVSE location. Install a hardwired EVSE. That avoids the GFCI requirement and is better anyway for a bunch of reasons.
  • You can gradually add circuits as needed and/or move circuits from the existing subpanel.
  • Abandon the old handle-tied 30A breakers and the wires attached to them. That avoids having to track down the hidden junction box. The spaces freed up can be used for other circuits. (Actually, if you don't have anything to put in there, leave the breakers in place so you don't have a hole in the front cover. But disconnect the wires.)
2
  • 1
    I have some experience with handle-tied 240 breakers that did in fact provide common trip. The breaker spring was powerful enough to trip the tied breaker. But do you really want to short one side of 240 and test it to see if you have such a beast today? I'd rather not.
    – Joshua
    Commented May 25, 2023 at 3:46
  • Thanks! I posted diy.stackexchange.com/questions/273005 with more photos of both panels. Please let me know there whether I need a subpanel. Let's keep this question focused on the unsafe NEMA 10. If I can install a water heater I'll likely run a new wire for the dryer, see diy.stackexchange.com/questions/273007 If not I'll have to locate the hidden junction box...
    – user162793
    Commented May 25, 2023 at 11:31
5

Kill that NEMA 10 with fire before it kills you with... well, shock

Wow, so the house was wired with a 4-wire dryer circuit, and they extended that with 3-wire (using 10/2+gnd). That's a crime. Literally, if a kid got shocked to death they'd be charged, like this guy.

So no, I'm sorry to say that "10/2+ground" dryer circuit extension was illegal the day it was installed.

Burying the splice box was also illegal. If you have to tear off built-in cabinets to gain access to the box, that violates the rules for box access. (leaning a placed cabinet up against the wall is fine if you don't screw it in, or if it's a KALLAX style where you can reach through.) This hackery should have been listed in the seller disclosures, and there's liability for them if they didn't.

On the other hand, if they used a metal box for the extension the original was probably a metal box too. That will make it easier to find non-destructively. If you can find the original box and make an access hole in the back of the cabinets, you can probably get into that wall and run the proper 10/3+ground cable they should've. SMH I'm sure glad they saved that dollar...

Once you have separate neutral and ground at the dryer outlet, smash all NEMA 10 plugs and sockets with a hammer to prevent reuse - they are dangerous. Use a NEMA 14-30 socket and change the dryer cord to 14-30. Make sure to remove the neutral-ground bonding strap on the dryer, per instructions for changing cord.

As far as I'm concerned, this is a repair to incorrect work that does not require pulling a permit, and does not consist of installing a new receptacle that would place you under the "GFCI required" NEC 2020 rules. (if your state is on NEC 2020). If you want to be picayune, see NEC 406.4(D)(1). *

About EV charging...

If you are not encumbered by NEC 2020 rules or your state waived that rule, or if a GFCI breaker is not a showstopper for you**, feel free to install a second NEMA 14-30 or NEMA 6-30 recpetacle at a location of your choosing. (you could even reuse that 10/2 wire with a 6-30 recep). NEC does not place any limit to the number of outlets on a >>! general-use !<< 30A circuit. However, the conceit here is that you plug all sorts of things into it - kiln, compressor, welder, EV, bandsaw, whatever comes up. You can't assert that the socket is dedicated to EV charging because it would require a dedicated circuit if so.

I realize we're playing fast and loose there while I'm being militant about killing NEMA 10. That's correct. One is word games and they other kills several people a year. (it electrifies the chassis of the dryer if the neutral wire breaks, because dryer frame is bonded to neutral. John Ward explains the badness of combining neutral and ground, in a British context. Those poor people are having a hell of a time safely charging EVs.

If you're thinking "not sure I trust that breaker, it belongs in a breaker museum", that's an $18 problem. You won't find the correct Murray MP230 in stores but Siemens re-branded Murray to Siemens, and UL has a letter saying "QP line" Qxxx breakers are the same as MPxxx breakers. Q230 and Bob's your uncle. Torque screws to spec.

That Load Calculation

A NEC Article 220 Load Calculation is an exercise worth doing. Your municipality has a worksheet. If the Load Calc either a) have room for the dryer but not the EV (would surprise me) or b) you really, really want 50-60A charge rate... then you can use a technique that Zappi called "Grid Limiting". That works with a companion module that sits in the panel and has clamp-on "CT" ammeters on the service wires. Fact is, house loads are very spiky - the average American house averages only 5 amp draw, even though it needs a 100-400A panel to accommodate peaking. If you know anything about averaging, that means most of the time, load is well under 5 amps. So there's plenty of power most of the time; the nut is knowing when, and that's what the clamp ammeters do. EV charging is able to be dynamically adjusted on the fly because it was designed for that.


* Even though 406.4(D)(2)(a) would permit in-kind replacement of NEMA 10 with NEMA 10, that would only work if the cable was legal, and it's still dangerous. If GFCI is no object, then 406.4(D)(2)(c) still doesn't help because the cable is illegal for that use.

** Though, a GFCI is a waste for EV charging since the EVSE contains a better GFCI.

2

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.