Our new dryer has 3 prongs vs. 4. We are changing to the new 3 prong dryer outlet, but want to make sure we are grounding. The wires coming from the wall our white, red & black - the the copper wire.
Do I need to ground it??
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3What make and model is the "new" dryer?– ThreePhaseEelJun 17, 2017 at 22:28
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Can someone add pictures? What do you mean four prong. Ive never seen this and have been born in the usa i have no idea what you are talking about.– JonHJun 18, 2017 at 13:51
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@JonH -- the OP is referring to the distinction between NEMA 10-30 and NEMA 14-30– ThreePhaseEelJun 18, 2017 at 14:56
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4 Answers
Switch the cord, not the socket
You have a proper NEMA 14-30 dryer receptacle with a ground wire, which is good. However, your "new" (old) dryer has a 3 prong (NEMA 10-30) cord. This can be rectified -- get a 4 prong (NEMA 14-30) dryer cord and install it on the dryer in place of the existing cord, making sure to remove the neutral-ground bonding jumper in the dryer.
answered Jun 17, 2017 at 22:29
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What's the fourth prong for? Is this a North American thing that uses two phases of a 110V supply for higher power? Jun 18, 2017 at 11:12
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3@DavidRicherby yes, in the USA we center-tap our 240V supply. And call that neutral and bond it to ground. This is not entirely unsimilar to how the UK provisions construction site power (110 center tap grounded). They're not really two phases, it's the same phase. We call it split-phase. We do not bring 3-phase "wye" down local streets. Jun 18, 2017 at 14:19
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1There should be a wiring diagram on the dryer, or in the manufacturer's installation instructions. Make sure you follow the instructions for wiring the new 4-prong cord. Jun 19, 2017 at 12:42
You are not grounding, and this can kill you
I have no idea why you think 3-prong sockets are new. They are obsolete and dangerous. They are "exactly what they look like": the 3-prong outlet omits the ground, and the 4-prong outlet adds the ground.
Any problem with the neutral wire will result in the dryer frame being energized at 120V. Touching that and anything grounded, like the washing machine right next to it, will shock you.
It is illegal to convert a 4-prong to 3-prong. The home improvement store will happily sell you one, but they are only legal to sell for like-kind replacement which is not what you are doing.
The appliance manufacturers got a loophole put in Code so they could continue to sell appliances to old houses wired with the 3-prong outlets. In this case they bootleg ground, which is as bad as it sounds. Why on God's green earth the appliance store let one go out with a 3-prong plug is beyond me.
When reconfiguring the dryer for a 4-prong cord, make sure to remove the neutral-ground bootleg jumper. Neutral should be separate from ground.
The official name for the 4-prong is NEMA 14-30. The official name for the hazardous 3-prong is NEMA 10-30. Not to be confused with the safe but useless-for-your-dryer NEMA 6-30, which does have ground but not neutral.
answered Jun 17, 2017 at 23:10
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Who lives in an older house. Well, even "old" (Read 15 year old) dryers will be made to take 4-prong cords. Though you can always steal the cord off the outgoing dryer... Jun 18, 2017 at 3:05
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Yeah, that'd do it. We're stuck with NEMA 10 over here :/ (50's vintage house) Jun 18, 2017 at 3:12
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2@Xen2050 and all the other reasons to keep neutral separate, of which there are many. Grounding is not a copper industry conspiracy, at least that's what they pay me to say! The fact that they're bonded at the panel doesn't make them the same thing. It's merely to peg neutral at a near-ground voltage, to reduce its hazard, and this is only done in one place. Google "why are ground and neutral separate in subpanel" for more on that. . Jun 18, 2017 at 14:26
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2And really nothing says neutral and ground must be bonded at the same voltage. If your supply transformer had a tap that was 3v off center, you could bond your ground to that, and there'd be a 3V difference between neutral and ground. This would still serve every purpose of the neutral-ground bond. The point is, you need to bias neutral to something, otherwise it's biased to nothing and you'll have an isolated system and it will rattle/float, potentially at 2400V if the supply transformer has primary-secondary leakage. Jun 18, 2017 at 14:35
Arriving late to the party...
I wonder if this was Bosch or Miele dryer. While both use 3-prong outlets, neither Bosch or Miele can be connected to old ungrounded 240V 3-prong NEMA 10-30 outlet.
Bosch uses 3-prong 240V NEMA 6-15 outlet (both for washer and dryer), while Miele uses common 120V NEMA 5-15 outlet (also for both washer and dryer, but requires dryer to be on a dedicated 15 amp circuit). Both of those are 3-prong outlets, both do have ground, and both are perfectly safe. Unlike the old unsafe NEMA 10-30 which doesn't have ground.
So, if it was one of those two dryers, you all scared Molly for no good reason ;-)
If it was Bosch or Miele, while it is possible to replace 4-prong NEMA 14-30 for either 6-15 or 5-15, it doesn't make sense to do that. It'll have to be done by electrician and it's going to be a bit pricey to do. It'll also mean if she was to get a new dryer 10 years from now, she might need to get electrician again ($$$) to rewire laundry room back to 4-prong NEMA 14-30 outlet, because that is what almost all other dryers require.
Instead, both Bosch and Miele sell inexpensive adapters that plug into NEMA 14-30 outlet and have two NEMA 6-15 (Bosch) or two NEMA 5-15 (Miele) outlets, each of the two outlets with 15 amp fuses inside the adapter itself. You simply plug both washer and dryer into the adapter. And that's it. Done.
Because people don't tend to have 6-15 outlets in their house, or 5-15 on a dedicated circuit (i.e. not shared with any other outlet in the house), it's a bit odd choice on Bosch and Miele part to sell dryers in the US with those plugs. But it is what it is. Just get the adapter. On the positive side, at least it is impossible to plug those dryers into old ungrounded 3-prong NEMA 10-30 outlets. Unlike almost all the other dryers that can be wired to connect to that old unsafe outlet.
I'm surprised nobody at the store said anything or asked what type of outlet is in the laundry room, and sold the adapter with the dryer. Literally every time I looked at Bosch and Miele dryers (which was like two times), that sales person asked me what type of outlet I have.
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Interesting info and you're right, a very odd decision on Bosch & Miele to sell this in the US.– FreeManSep 3, 2021 at 12:12
I was just reading this and was going to comment about the "good old days" syndrome, when something hit me. Usually a dryer receptacle only has three prongs. I almost got caught up in the same argument, but a dryer has no need for a neutral it runs off of 240V not 240/120V and a standard receptacle provides slots for both sides of the 240V circuit and one slot for the grounding wire, and you usually run a 10/2 w/ ground romex to the receptacle.
I don't know why someone had a neutral for a dryer unless it was some sort of a special order. So he ordered a new dryer with the right configuration for a standard dryer. I would install a matching receptacle and wire nut off the neutral in the box.
answered Jun 18, 2017 at 14:39
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3Most dryers in the US run the heater on 240V but the timer and drum motor on 120V, sadly. I wish you could get dryers that plugged into a NEMA 6! Jun 18, 2017 at 14:57
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I have seen small dryers that were 120v very rare in the U.S. The heating element is 240v on most and is the big power consumer at close to 5Kw on most.– Ed BealJun 18, 2017 at 15:09
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I'm only going with the information that was given. @molly says it is a new dryer. That tells me it came with the right correct configuration. So the real check would be a the nameplate as required by NEC article 422 Appliances. Some run off 240V and some run off 240/120V. That would be the real place to check. Jun 19, 2017 at 12:56