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About 5-6 years ago I bought a Samsung dryer, and at the time they installed it with a 3-conductor non-grounded power cord, because that was the kind of receptacle we had. Standard breaker, no problems. Now I'm building a new laundry room, and changed that circuit over to the new (Siemens) subpanel. Nothing has changed with the dryer or the receptacle, but now it is throwing the new 30A dual-function breaker in the subpanel. The breaker doesn't trip when the dryer isn't plugged in.

What could be causing the breaker to trip, that never tripped the old breaker in the main panel? And am I going to need to swap the power cord over to a 4-wire, grounded setup?

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  • who installed the new Siemens.
    – Traveler
    Mar 16, 2023 at 8:10
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    I'm not aware of anyone making 30A DF breakers... Mar 16, 2023 at 11:42
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    I think the OP is calling a GFCI breaker dual function, ground fault and shorts. We usually do not consider the main function of a breaker as separate, same as cables we do not count the ground wire, it is just there.
    – crip659
    Mar 16, 2023 at 12:52

2 Answers 2

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Actually, with a GFCI breaker, converting to 4-prong outlet is easy.

  • 4-prong NEMA 14-30 socket. Connect ground to nothing!
  • 4-prong dryer cord
  • Install cord according to the instructions (separate neutral and ground at the dryer)
  • Put a label on the socket saying "GFCI Protected - No Equipment Ground"

And you're done, safe & legal. No need to rewire, and the best safety option available.

Why?

Right now, you have the sad and somewhat dangerous situation of the dryer's metal chassis wired to the neutral wire. That is functionally a bootlegged ground. But now, it is under GFCI protection! GFCI protects (monitors) hots AND neutral for leakage. Any leakage from neutral to ground is a ground fault and will trip the GFCI. Remember, the dryer's chassis/frame is attached to neutral.

So if the dryer chassis touches anything, or if you simply touch both grounded washer and dryer, you are creating a neutral-ground "ground fault" and that will trip the GFCI. Working as intended.

So by separating the dryer's chassis from neutral, we stop that from happening.

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Most likely this is a ground fault causing the GFCI breaker to correctly trip.

Theoretically, a truly properly installed 3 wire dryer connection will not trip a GFCI unless there is a fault from the dryer cabinet through a person or pet or wet floor. A fault within the device would not cause a trip because of the long deprecated 3 wire connection.

However, there are a number of situations where a 3 wire connection can easily cause GFCI trips due to wiring, such as:

  • SE cable with a bare neutral. The bare neutral can easily short against the panel, so some current flows to ground, causing the GFCI to trip.
  • Neutral insulation failure at any point where ground is accessible (panel, possibly a junction box that is grounded despite not having a ground wire connected to the receptacle)

The solution is to convert to a proper 4 wire cable (or 4 wires and conduit or 3 wires and metal conduit). If any GFCI trips happen after that then you have a faulty appliance.

I switched my dryer from 3 to 4 in conjunction with panel replacement even though my electrician said it was not strictly required. But since the receptacle had to be rewired anyway and the receptacle is literally attached to the panel, it was super easy. Obviously if the dryer and panel are a long distance from each other it may be a much bigger task.

Make sure to remove the neutral ground bond from the dryer.

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