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I recently purchased my first home and the breaker the electric clothes dryer is connected to is 20 amp. I was told it should be 30 amp by a home inspector but foolishly did not have the seller correct it. If I run the dryer on its highest heat setting it will trip the breaker so I would like to swap out the 20 for a 30. How can I tell if the wiring and such is adequate for 30 amps?

Location: North-eastern U.S.

wire

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    This is an unusual situation, so tread carefully. Unless you can conclusively determine that the circuit is capable of 30 amps from end-to-end, you should not change the breaker. It's an important safety device.
    – Hank
    Commented Aug 8, 2014 at 19:31
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    If it is easy to do; I would just replace that cable as the outer jacket is deteriorating, and may not be adequately grounded to modern standards. Commented Aug 9, 2014 at 12:26
  • Modern standards nec 2014 250.114 then follow instructions on dryer to install a 4 wire cord.
    – user24125
    Commented Aug 9, 2014 at 17:07

5 Answers 5

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It depends upon two things:

  1. The gauge (thickness) of the wire; and
  2. The length of the wire.

For 30 amp, a typical household installation requires 10 gauge: enter image description here

To measure it you'll need to use a wire gauge measurement tool on an uninsulated piece of the wire: enter image description here

You can get these on Amazon

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    Virtually wire and cable has the gauge printed on the outside, that would be an easier way to tell.
    – Hank
    Commented Aug 8, 2014 at 19:29
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    Looking at the picture presented, I am curious - do you think the printing will be legible, if you can find it at all without stripping the wire more than it's already been stripped (as in permanently installed...) Commented Aug 8, 2014 at 19:53
  • I couldn't read anything on the wire to see what gauge it is. Since it is in an unfinished basement I suppose I'll just run new wire.
    – Jeff W.
    Commented Aug 8, 2014 at 20:00
  • You need to go by the material of the wire, as well. Copper can hold more current then aluminum. I don't know the popularity of one vs the other. Commented Aug 10, 2014 at 17:15
  • For completeness, that particular drop from the ceiling to the outlet "should" be conduit protected or armored (BX) wire. Pretty common but against code :-/
    – hylander0
    Commented Jun 16, 2016 at 18:57
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The easiest and surest way to determine the gauge is to look at the bare wire itself, either in the outlet, or more easily in the service panel where it goes into the breaker. It is almost certainly one of 14, 12, or 10 gauge wire.

If you haven't worked with much electrical wire, then sighting its diameter it won't be as easy, so simply compare it to a known gauge wire, perhaps in the other breakers. Or go to your local electrical supply store or big box retailer and look and feel the wires. Maybe even buy a foot of each to keep as reference.

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    You'll also want to make sure the same size wire runs the entire length of the circuit.
    – Tester101
    Commented Aug 8, 2014 at 23:32
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A cloths dryer needs to be fed by a 30 amp circuit through at least#10 awg copper wire (I don't recommend aluminum) if you do find that the wire you have is#10 ga. Copper make sure that it has 3#10 conductors and is not using the very small bonding conductor that old romex like that usually has for the neutral.

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Check the wire gauge before replacing. I had an old Victorian and similar wire was 10-gauge copper, some of the best wire in the house; I wrapped the exterior in wide electrical tape.

Also, your breaker should be dedicated ONLY to the dryer, even if that is not the code in your area. This makes swapping out the wire and breaker fairly straightforward, and if it is 10-gauge, swapping out the breaker is incredibly easy. Just have to turn off the power main to the whole house, which is usually at the top of the breaker box.

Good luck!

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    how do you check / verify that it's 10 gauge wire?
    – Ack
    Commented Dec 29, 2020 at 23:12
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Why not just run the dryer for a few months and see if the 20 amp breaker trips? If not, then 20 amps will do fine. It's possible that your dryer doesn't pull more than 20 amps.

20 amps times 220 volts means a maximum of 4400 watts. If you look at the back of your dryer it may indicate the wattage it consumes.

If the line isn't buried behind a wall, it probably would be easy just to replace your existing line with 10 ga copper conduit. I suspect it's a straight shot from outlet to panel with no junctions. It should take a pro less than 30 minutes.

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    OP already said the breaker trips when dryer is on "high".
    – Hank
    Commented Aug 8, 2014 at 19:29
  • Hardly anywhere in the U.S. gets 220 volts. It is likely to be 230 in the northeast and wherever there is heavily loaded transmission. The rest of North America gets 240 volts. Also, a 20 amp circuit is not rated for 20 amps continuously. There is a 20% derating so 16 amps is all that can be used. 16 amps times 240 volts is 3,840 watts.
    – wallyk
    Commented Aug 8, 2014 at 20:05
  • I am in the Northeast (NY State). My household voltage is consistently 240-250V. Also, a household dryer would NOT be considered a continuous load. This is not to say if the cable is 10 that the breaker should not be changed to 30A. It should. Commented Aug 8, 2014 at 21:42
  • @SpeedyPetey: You are correct. I thought the definition of continuous was 30 minutes or more. This says it is A load where the maximum current is expected to continue for 3 hours or more. I have been overly conservative in my electrical work.
    – wallyk
    Commented Aug 9, 2014 at 0:08
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    Wallyk: no you are not too conservative the dryer outlet is a 30 amp device it needs to be fed by a 30 amp circuit with the correct wire.
    – user24125
    Commented Aug 9, 2014 at 16:57

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