How can I safely utilize a dryer outlet to power 100V and 220V loads?

Question

In my house there is a dryer outlet that, even though inconvenient to me (my dryer is 120V), I don't want to eliminate for house reselling reasons. As it was until now a 3 prong outlet, I have been connecting my dryer through an external box that I built, which is shown in the picture

External box that connects to the dryer outlet

The box is fed by a dryer cable connected to the outlet that carries one hot and the neutral to a 20A GFCI outlet (the second hot conductor was terminated open in the outlet). I put a push-resettable 20A breaker (the push button is visible on the right side) between the hot conductor and the GFCI receptacle that allowed me to protect the box without having to mess with the breaker panel. This has allowed me so far to safely use my dryer without doing any permanent modifications that could result in NEC violations.

As I was recently able to add a grounding conductor to the dryer circuit, I am now envisioniing ways to modify my box into a "2-gang box" to make it more useful. The feeding will be through a 4-prong dryer cable attached to my new grounded outlet. On the left side I will keep the existing configuration (just adding the ground connection) while on the other side I am planning to insert a dual 120/240V 20A duplex receptacle that would allow me to use directly some 240V European appliances, getting rid of a bulky 3000VA step up transformer whose safety I don't fully trust.

My question is: can I do this in a safe way by just adding a second resettable 20A breaker to the other hot conductor, as shown in the scheme below?
The wires inside the box are 12AWG, with overcurrent in the two hots protected by two Carling miniature 20A thermal circuit breakers, and the dryer circuit is protected in the panel by a Eaton BR 30A dual pole breaker. Being an external box, I am not concerned about the letter of the code, but I am of course concerned about safety.
I can think of at least a couple of issues on which I would like to get some advice. The first is the fact that the Carling breakers in the box are independent. If that was an issue, I believe it can be overcome by replacing the 30A dual pole breaker in the panel with a 20A one. The second is that the mixed 120/240V receptacle is not GFCI. However, it is grounded and GFCI is not a requirement for the 4-prong dryer outlet. This could be also be overcome by using a dual pole 20A GFCI breaker in the panel, but I woud gladly not spend the extra money if it was just an overkill.

Any advice, suggestion, critique is highly appreciated

NOTE: it would be great if I could find a duplex outlet with the 240V side having that universal shape that can directly accept European male plugs. Does anyone know if it is available?

Answer 1

TLDR: since you now have a NEMA 14-30 receptacle, you can install a UL-listed device called PDU that plugs into that and provides whichever 120V or 240V loads that you require.

What you're planning to wire is called a Multi-Wire Branch Circuit.

The first is the fact that the Carling breakers in the box are independent. If that was an issue, I believe it can be overcome by replacing the 30A dual pole breaker in the panel with a 20A one.

Yes, that certainly is an issue! You need common trip for 120V/240V loads like dryers. You also need it for MWBC's when they serve both 120V and 240V loads, and since that is your plan, you need common trip. That can only happen at the breaker.

(for your information, MWBCs with only 120V loads do not need common trip, but do need common shutoff for maintenance. The same is true of 240V-only (no neutral) loads.)

Reading this question, I can't believe you're fooling around with fuses. I first assumed "oh well, you have weird old breakers and you CAN'T replace with a 20A/2-pole"... but since you just casually toss that out as an option... yeah. Do that.

"making it harder than it is" LOL.

I'm assuming your panel actually is a Westinghouse, Challenger, BRyant, Cutler or Eaton panel that is supposed to take a BR/C type. If it's not, use the correct breaker - it matters. We can help.

Now the hinky breakers can go away out of the box. The box itself isn't so bad if it's well-made, impact resistant and isn't at risk of knockouts breaking off from handling (as it would if you used a standard 99 cent 4x4 box). In fact OSHA has argued that they should be permitted.

However once you re-breaker to 20A, the NEMA 14-30 socket shouldn't be involved. NEC 210.21. If it is a flush-mount socket (i.e. a junction box behind it), then remove the 14-30 and get a mud ring or extension box that is 2-gang (we can help you with that), and just put your sockets directly into that box.

Or if you prefer, you can use surface conduit such as Legrand Wiremold to extend off that box and bring your receptacles to a more convenient location.

The second is that the mixed 120/240V receptacle is not GFCI.

Yes, that's an irreconcilable problem. Since it is in the laundry room, the 120V receptacle requires GFCI protection. Under the circumstances, this is best done at the breaker.

However, it is grounded and GFCI is not a requirement for the 4-prong dryer outlet.

Check your state's adoption of NEC. If they adopted NEC 2020, then yes, in fact, 240V receptacles in laundry rooms DO need GFCI protection. And the breaker is the only way to do that.

I woud gladly not spend the extra money if it was just an overkill.

Except you already spent more than that in money and time building the hack box, so I don't have a lot of sympathy lol. You could have done it correctly at the outset.

NOTE: it would be great if I could find a duplex outlet with the 240V side having that universal shape that can directly accept European male plugs. Does anyone know if it is available?

NO. I know the ones you mean, and they'll never get a UL listing because it is impossible to build one that makes reliable contact on all plug types, while rejecting plugs that don't belong there (such as NEMA 1-15). They are Chinese "specials" intended for USB phone chargers, not running a kettle. Forget it.

And certainly, you'll never find a combination NEMA 5-15 + BS1363 or NEMA 5-15 + CEE 6/3 socket. Not least, there are dimensional issues - they won't fit! Euro gang boxes are bigger for a reason.

If you have a particular Euro connector you want to adapt, then simply buy any quality, approved run-of-the-mill extension cord for that socket, lop off the plug, and install a NEMA 6-15 plug.

Or just change the appliance plug to NEMA 6-15. Will that appliance really be going back to Europe ever?

If you want AU/NZ sockets, nice surprise, they use the same form-factor for their junction boxes, so a 1-gang AU/NZ receptacle will bolt right into our boxes. But you'll still need a whole "gang".

By the way, if you move the GFCI to the breaker, you can fit a plain 120V socket on the left, break the tab on the hot side and "split it". That's commonly done on MWBCs.

that would allow me to use directly some 240V European appliances, getting rid of a bulky 3000VA step up transformer whose safety I don't fully trust.

Let me guess, Chinese crud with that "universal" socket?

Even our biggest 120V circuits are only 2400 VA, and a lot of European appliances are bigger than that. So this thing is a recipe for circuit overload.

You know, you sunk some serious coin and time into a lot of this stuff. Doing it properly isn't so expensive by comparison.

Answer 2

I am not sure if this is the most appropriate way to proceed, but I wanted to summarize what I got from the discussion into a workable solution, which mostly follows the lines of the New breaker and MWBC solution proposed by @manassehkatz (in the sense that he deserves the credit for the solution and I deserve the blame for any potential misinterpretation of what he wrote). Rather than modifying the initial post, I believe more appropriate to present it as a solution, which can be criticized if necessary.

First of all, thanks to all those who took time to provide me feedback that improved the design. After modifying the original design as shown below,

using a metal box instead of plastic, and protecting the dryer circuit with a 20A/2-pole breaker (and with GFCI functionality under the provisions of NEC 2020), the plug-in box provides a safe way to use an existing 4-prong dryer outlet to power 120V and 240V loads that do not exceed 20A. The only point that is not theoretically code-compliant on the non-removable part of the circuit is the use of the NEMA 14-30 outlet in a 20A circuit. This is, however, not a concern in practice as long as the outlet is used exclusively through the plugged in box. When selling the house, full NEC compliance can simply be re-established by unplugging the box and substituting back the 30A/2-pole breaker at the panel (GFCI under NEC 2020)

FINAL NOTE
In the final design I decided to eliminate the 120V outlet connected to the red phase (the bottom right outlet in the figure) and have just the 240V outlet on the right side. Since a third 120V outlet was not really needed, its elimination prevents those potential issues with an open neutral that affect all MWBCs that power hot to neutral loads from both phases.

Answer 3

Your kludge worked and was a reasonably safe alternative under the circumstances. But you really (for a bunch of reasons) should be using 20A breaker in the panel to match your 20A receptacle. I see two possible solutions:

• Subpanel

Yes, that may seem like overkill. But it is a very practical, all encompassing, solution. Of course, that depends on having a proper place for a subpanel (it needs the same open space in front of it as a main panel). You would feed it, for now, the existing dryer circuit. That would give it a limit of 30A. From the subpanel you can then have your new 4-wire dryer receptacle (that you aren't using, but that way it is there for future users) and as many 120V or 240V 15A or 20A circuits as you like. The only catch is that you have to limit total usage at any one time to 30A @ 240V (24A continuous).

• New breaker and MWBC

Replace the existing 240V 30A double breaker with a 20A double breaker. Now you have a 20A Multi-Wire Branch Circuit. That can be used for 120V and/or 240V receptacles, with a limit of 20A.

Either way, you have the GFCI issue. While you used GFCI until now as a way around the lack of grounding (which is a good idea and supported by code even if your kludge isn't), in most areas (depends on local NEC version in use), new receptacles in certain rooms, typically including the laundry room, require GFCI protection. Assuming that is the case, you most likely need to have GFCI on all 120V and 240V 15A and 20A receptacles. For 120V it is easy - you can use the same type of GFCI that you already have. But for 240V that will normally mean a 240V double-breaker with GFCI included. Yes, that costs more. But it has the advantage of working well with 240V circuits and can protect an entire MWBC (otherwise an MWBC used for 120V will need two separate GFCI/receptacles, wired properly, for the two halves of the circuit, and then neutrals must be kept separate after the GFCI split).