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I have a new Whirlpool dryer with a 4 prong cord.

I have a 3 prong outlet in my wall with two 10 awg hot (black) and one 10 awg insulated green ground. In the circuit panel, the two hots are connected to a double 30amp breaker. The insulated green goes to the ground bar. There is NO dedicated white neutral from the panel to the outlet box.

I am upgrading to the 4 prong outlet and wondering what my options are … to me, it seems I need to run a 10 awg white neutral from the panel to the outlet box and add it to the neutral bus bar and to the 4 prong outlet to complete the install. Please let me know if this is correct or if there are any other options. Thanks

brhans
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Alex Rodriguez
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2 Answers2

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3-prong dryer/range outlets are hot-hot-NEUTRAL

Not ground. Your "last guy" actually used the wrong color wire, which leads you to believe that third wire was ground. It's not.

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I can see where this can be confusing, but just as there used to be "groundless" 120V outlets, the NEMA 10 is simply the "groundless" version of the NEMA 14.

What's the big deal?

The big deal is that neutral is the regular current return. It's supposed to be near ground, but if the neutral wire breaks between the appliance and panel, neutral will "float" up to 120V. That is normal, and that's why we insulate the neutral.

Simple loose connections or wire breaks happen all the time, and shouldn't make an appliance dangerous. But in the case of dryers and ranges, the 3-prong wiring procedure grounds the chassis to neutral (we would call that "bootlegging ground" anywhere else). This means a neutral wire break or loose connection guarantees the chassis will be electrified. And it's metal and sitting right next to a grounded washer chassis.

They were given a pass in 1966 when grounding was required for everything else. The rationale was that these sockets are rarely disturbed, so a neutral wire failure was unlikely. Eventually this accumulated enough of a body count for NFPA to act, and ban it in 1996. It's still happening because of legacy installations, but it's mis-reported as incorrect wiring -- when actually it was correct wiring that failed. Because usually the newspapers see it because someone sued the landlord alleging mis-wiring. The landlord is blameless. Wire failures can happen to anyone.

Harper - Reinstate Monica
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  • I thought this may have been the case at first. I followed the green insulated 3rd wire to the panel and it connects to the ground bus bar with other grounds. A wire connected to the neutral bus bar is missing all together. Adding a 4th wire which should I dedicate it as? I’m still thinking as a neutral connected to neutral bus and neutral slot in the outlet. – Alex Rodriguez Mar 17 '22 at 21:46
  • @AlexRodriguez -- correct, pull a 10AWG white wire through the existing conduit and land it on the neutral bar – ThreePhaseEel Mar 18 '22 at 02:18
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I need to run a 10 awg white neutral from the panel to the outlet box and add it to the neutral bus bar and to the 4 prong outlet to complete the install.

this is correct,

You might have to dig around for pull points if the conduit is too bendy.

Another option if that doesn't work out is to check the manual of the dryer and see if they allow a 3 cord (hot hot ground) install and follow the instructions accordingly.

ratchet freak
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    Thanks. Luckily the dryer is within 10 ft of the panel so snaking the wire shouldn’t be too difficult. – Alex Rodriguez Mar 17 '22 at 13:33
  • I'd just go with the hot hot ground approach -- I think that this was standard in the US until 1996 or 2000, and you'd have to replace the wires, the outlet, etc etc, versus changing a cord. – gbronner Mar 17 '22 at 15:37
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    @gbronner It's less safe because it uses the ground as a current carrying conductor. Future proofing with a proper neutral is better in the long run. – ratchet freak Mar 17 '22 at 15:44
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    @gbronner No, the old-style 3-prong connection was hot-hot-NEUTRAL without ground. Look up the NEMA 10 spec, it says just that. Even worse, it involved attaching the dryer chassis to the neutral, meaning a simple loose neutral wire making poor contact was guaranteed to energize the chassis of the dryer. At least the dryer would stop working; can't say the same for ranges, where only the clock and oven light would fail. This was a hot mess (literally) and had a body count. OP's installer used a green neutral, which is typical of the confusion around this. – Harper - Reinstate Monica Mar 17 '22 at 16:48