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I have this three-phase panel and I'm looking to add or convert an existing circuit for a US 220V residential (guessing single-phase) electric dryer. I have the 4-prong plug/enclosure and the circuit run distance will be about 10 feet.

Do I need a specific breaker aside from it being 50A capable?

Do I need to use a specific side of the panel?

three-phase panel diagram three-phase panel interior

4 Answers 4

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Wow, a Crouse Hinds panel where both Eaton BR and Siemens MP/QP breakers are approved. (see the first full width paragraph halfway down). You don't see that every day.

I have the 4-prong plug/enclosure and the circuit run distance will be about 10 feet.

Well done!

Do I need a specific breaker aside from it being 50A capable?

You need to use the breaker that the dryer instructions are telling you to use. I seriously doubt it's 50 amps. But on the upside, you can run wire appropriate to the instructions and breaker, so there'll be a cost savings there.

The reason is that UL doesn't certify the dryer for circuits larger than specified. E.G. they've made sure any foreseeable failure will trip a 30A breaker, but they can't promise it'll trip a 50A.

Do I need to use a specific side of the panel?

Yes. You need to be very careful about voltage to ground. Certain 3-phase configurations have a higher voltage-to-ground on one leg, also called the "Wild Leg". An example of wild-leg is seen on the panel diagram label, to say IF you are supplying wild-leg delta to this panel, the wild leg must be on phase B. However, your panel could nonetheless be simply 120/208V "wye" arrangement with equal legs.

I notice that NONE of your phase wires are marked orange. When wild-leg is supplied, Code requires the wild-leg be orange. So I'm going to bet you don't have wild-leg. If all phases are equal to ground (probably between 110V and 130V), then you're fine and you can place the breaker between any two rows. If you mean to put it in the 2 spaces on bottom left, that appear open, that should be fine. Use a Siemens Q230 or Eaton BR230 breaker.

You may measure 120-127V from both legs to ground and 208-220v between the two legs. That is FINE. The dryer will function just fine, but with only 75-85% power, it will "duty cycle" (switch the heater on/off) at a higher percentage of the time. Where it might be "on 30 seconds, off 30 seconds" on 240V, it'll be "on 40 seconds, off 20 seconds" for you.

Now, I see a great many "Multi-Wire Branch Circuits" aka MWBC aka shared-neutral (2 hots 1 neutral) on what appear to be old-fashioned tandems with unusual handle-tie arrangements. You must be very, very careful in this panel with moving any of that stuff around. On any given MWBC (black-white-red sharing a cable), there must be 208-240V between the black and red. I personally would use black-red-blue phase tape to tag each MWBC's wire for the phase it belongs on. If you want to see what phasing is about, read this Q&A here and let me color your panel similarly to that link.

enter image description here

I tinted the black phase a bit purple for visibility.

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    Wait wait wait.... is he installing a new 50 Amp cord and receptacle? Is that allowed on a 30 Amp circuit? Commented Feb 19 at 20:14
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    Epic answer! Thanks for the breaker guidance as well; I checked & then bought a 30A common trip double breaker after checking my dryer manual
    – Merrick
    Commented Feb 19 at 23:25
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    @RobertChapin I made a silly assumption I needed a 50A circuit based on the receptacle maximum; thanks to y’all’s guidance I’m now adding a 30A breaker/circuit
    – Merrick
    Commented Feb 19 at 23:26
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    @Merrick many used dryers have 50A range cords improperly installed on them. If the manual is saying 30A, change the cord and socket to 14-30. Commented Feb 20 at 23:20
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Do I need a specific breaker aside from it being 50A capable?

That is scary. And it is the second time recently that I've seen that reference, which is not a good thing.

Nearly all US residential clothes dryers are 30A, (240 or 208)/120 V appliances. 50A is absolutely wrong. (The dryers that are not 30A are either underpowered apartment dryers or heat pump dryers - they are less than 30A, not more.)

That being said, yes three-phase can complicate things.

You will need a 30A double-breaker, which will span 2 of the phases. In order to make sure things work correctly, you need to make sure that the voltage hot to hot on the breaker (i.e., between the two phases) is 240V or 208V (most dryers can handle both, but since a dryer is basically a resistance load, they will produce more heat == dry faster at 240V than at 208V) and that the voltage hot to neutral (for both phases) is 120V. If the voltages check out OK then run 10 AWG cable or wires (hot, hot, neutral, ground) to a NEMA 14-30 receptacle and you're all set.

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  • Thanks for the breaker guidance! I checked & then bought a 30A common trip double breaker after checking my dryer manual
    – Merrick
    Commented Feb 19 at 23:27
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The critical issue here is that if this is a high leg Delta 240Δ/120 panel and you install a 14-30 receptacle with one hot to the high leg (currently marked with blue painters tape) you have a 50/50 chance of the 120v motor being connected to the B leg, feeding 208v to the 120v motor, and burning it out.

This condition is recognized by the nameplate on the dryer, it should look similar to this:

enter image description here

Notice it has two KW rating, the top rating is marked 208Y/120 which is the most common 3-phase configuration, and the lower is 120/240 which is the common single family residential voltage. Notice neither is marked 240Δ/120, it is not approved for 240v Delta.

With a meter check your panel, if it is a 208Y panel each leg will measure +/- 120v to ground. You can plug a two pole breaker in anywhere it fits.

If Delta panel two legs should read +/-120v to ground and one read +/-208 to ground. You must only install a two-pole breaker that is not connected to the (blue taped) high leg 208v pole.

You likely need a 14-30 receptacle because the dryer instructions say so, and a 30A breaker since your overcurrent protection cannot exceed the receptacle rating.

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  • I know this label is for a range, I said "similar". It was what I found with a quick search, and the same condition exists with a range, you can toast the control board instantly. Commented Feb 20 at 17:22
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That dryer outlet should be 30A rated and use a 30A breaker. Or is this some kind of commercial dryer? Avoid the high leg with your breaker placement and you'll be fine. Measure the voltages at the outlet, you should see 230-240 line to line and 115-120 line to neutral or ground.

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  • They just as likely have a wye service which'll be 208-215/220V L-L instead of 230-250V L-L, and won't have a high leg... Commented Feb 21 at 3:00

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