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I just bought my first home and I need to replace my 4-prong cord on my dryer to a 3-prong. I've removed the four prong and now I see this:

the green wire on the four prong was screwed to the left side of the unit

I know how to hook up the three prong, I'm just unsure about how to ground it properly. I've read online and saw a few posts here, but most point to the installation manual for the model as the best solution--which I've read, but I don't feel 100% that I understand. My manual has this configuration for a three-prong cord:

Samsung Manual Screenshot

It also notes that, if I'm converting from a four-prong, I need to "connect the ground strap to the terminal block support to ground the dryer frame to the neutral conductor."

How do I do that?

Do I take the loose white wire and assume that's "A" in the manual diagram and attach that to the side of the unit? The loose white wire was originally in the neutral slot with the neutral on the four prong cord, should it go back there? Do I need to do anything with the green wire?

I'm pretty lost at this point so any guidance would be greatly appreciated. Thank you!

  • If at all possible, try to convert the wiring to support a four prong outlet. It is much, much safer, protecting you and your family from potentially fatal currents if there is ever a wiring fault (nothing bad ever happens, right?) – user4302 Mar 6 '17 at 2:42
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    Seriously. What @Snowman says. Those obsolete NEMA 10 receptacles kill people. It's rarely reported, or is misreported as a "miswired receptacle" when it's really just a wiring failure. – Harper Mar 6 '17 at 6:43
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You're asking how to ground it properly.

The instructions are telling you to do something which is not proper. NEMA 10 receptacles don't have ground. So they are telling you to misuse the neutral wire as ground.

In any other application, this would be called "bootlegging ground" and you'd fail a home inspection for it. However, appliance manufacturers have lobbied the NFPA to allow this for dryers and ranges so they don't lose appliance sales. The rationalization - which doesn't make much sense to me - is that dryer receptacles are rarely unplugged, so they're not likely to have a failure.

The failure mode is that if there's any problem with your neutral wire anywhere in your house wiring or dryer cord, the 120V loads will stop working, and the current path through them will connect neutral - and thus the dryer chassis - to 120V. You're dead if you touch the dryer chassis and any other ground. Such as the washing machine right next to it.

Option 1: Ground it, properly.

Don't mess with that heavy 10/2 cable; retrofit a ground wire. This is legal and encouraged. The builder supply sells #8 ground wire by the foot, and it's no bigger than telephone wire. #10 would suffice if you can get that cheap.

Use any feasible route to get back to the service panel that powers the dryer circuit. You do not need to run the ground wire with the conductors, because the ground wire does not carry current except during a fault condition. You don't even need to go back to the panel if you can reach something else that has a #10 ground path back to the panel (water heater, A/C, range). Circuits can share ground as long as they come from the same panel.

Then, install a NEMA 14-30 receptacle. If the neutral is bare, that's allowed because the cable is grandfathered, but wrap it (and the ground, if necessary) with tape so they don't short out. Neutral is not ground, and will be a fraction of a volt higher than ground when the machine is at full load, and you don't want it taking ground as an alternate path.

Option 2. Don't ground it; properly.

Here you leave the wiring, but render it safe. You change the 2-pole breaker in the service panel to GFCI. When the person starts to be shocked, the GFCI trips and saves them.

You must then change the receptacle to NEMA 14, connect nothing to the ground pin, and add a label "GFCI protected / No Equipment Ground". Then you need to change the dryer cord to NEMA 14, following all dryer instructions on how to remove the bootleg neutral-ground bonding on the dryer.

At this point the dryer chassis will "float". A neutral failure will not energize the dryer. A ground fault inside the dryer will electrify its chassis, however that should trip the GFCI before harming a human.

This method only works as a retrofit. It can't be used on new installations; those must be grounded NEMA 14 from the outset.

  • My dryer is currently wired with no ground with a 3-prong plug to a NEMA 10-30 receptacle. I am sure that on the terminal block of the dryer the neutral is bonded to the ground. So if I put in a 2-pole 30-A GFCI breaker, I don't have to do anything else, right? But if I later add a ground and change to a NEMA 14-30 receptacle, the GFCI breaker can stay in place, right? – Jim Stewart Mar 6 '17 at 18:55
  • @JimStewart I sure think so, yeah. I mean normally with GFCI we are thinking in terms of 120V receptacles but the principle applies. GFCI is the quickest way to get a lot of protection without having to fool with wires. Given that a dryer is a metal-chassis piece of equipment, that metal chassis works against you without proper grounding, and works in your favor with. And they complement each other very well. – Harper Mar 6 '17 at 19:12
  • This is a fancy new Samsung dryer and I must assume it uses 120 V as well as 240 V. Current is flowing between L1 and L2 and between at least one of the lines and the neutral. Will a GE THQL2130GF work? superbreakers.net/… It currently is powered through a GE 30-A double pole breaker. – Jim Stewart Mar 7 '17 at 13:43
  • @Harper -- GFCIs don't work with NEMA 10 ranges/dryers as-is (the bootleg jumper thwarts that -- you'd have to pull the jumper and float the chassis of the appliance to do that) – ThreePhaseEel May 31 '18 at 19:06
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    @Harper -- actually, one could GFCI protect a NEMA 14 and label it "No Equipment Ground" and "GFCI protected" using the provisions in 404.6(D)(2)(c) no? – ThreePhaseEel May 31 '18 at 23:59
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Yes, the loose white wire is the strap you're looking for -- it is indeed "A" in the manual diagram that attaches to the unit's chassis and bonds the ground and neutral together at the unit. (NEMA 10 sucks, I know, but it's often impractical to replace a single circuit without ripping a whole bunch of stuff up. The good news is that once you retrofit, you can simply go in reverse to convert your dryer back to NEMA 14 operation.)

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