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Just moved into a house built in the 1950s and, I discovered that one of the hot prongs for my dryer plug is giving me 120VAC (A in picture) and one is giving me 60VAC (B in picture).

3-prong dryer outlet

In addition, prong A (I believe this is the red wire) is just a single, solid copper wire while prong b (black wire) and the neutral (white wire) are both copper strands. I realize this setup is not correct, but I'm wondering what specifically needs to be fixed. Is this something I need an electrician for?

  • Posting a picture of the wires would be more helpful than the front of the socket if you have it available. – JPhi1618 May 28 at 17:30
  • Are these wires going through conduit or are they loose? What are the sizes of these wires? This is very strange; if there was a loose connection of the black wire that had 60 V across it, then it would be getting very hot (when the dryer was running) and you would detect it either in the panel or in the receptacle box! I would say it's time to call an electrician. It would not be safe to run the dryer with this condition, even to test. You miught start a fire. – Jim Stewart May 28 at 19:12
  • Can you turn the breaker off and get us photos looking into the back of the box for the dryer outlet? Something seems wrong here.... – ThreePhaseEel May 28 at 22:17
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This is an obsolete type of dryer socket and it should be replaced with a newer 4-prong style that includes both NEUTRAL and GROUND. Yes you probably should contact an electrician to pull a new wire and hook it up properly. Since it's clearly not right as it is, you should get it fixed properly.

  • Replacing a 3 prong dryer socket just isn't feasible in many cases, but if the red and black wires are in fact mismatched, this could be the best option. – JPhi1618 May 28 at 17:31
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Good eye spotting the mixed wire types. There is only one case where you'd ever expect to see that: individual wires in conduit. Given that this is a plastic box, the chance of this involving conduit is practically nil. This type of box doesn't even come with knockouts for conduit.

The blue plastic box suggests newer than 1989, so the 3-prong dryer receptacle should have been outlawed at time of installation. It has no ground, and worse, it relies on neutral for ground, so if the neutral breaks, it energizes the chassis of the dryer! This has killed people.

What most likely happened is someone ran /2 cable, hoping to get away with that (H1=black H2=white N=bare) but found out that is not legal, so they got a loose red THHN wire and ran it along with the cable. That is illegal too.

First a THHN wire isn't armored, but mostly, all wires in a related circuit must be in the same cable or conduit. That is because they kick considerable electro-magnetic fields. When they are bound together, those fields cancel each other out. When not bound, they vibrate and cause metal fatigue, or heat metal things between them (staples!) Either one can start a fire.

There's also a fair chance he used a #12 or #14 wire instead of the #10 appropriate for a 30A dryer circuit. If so, that would also result in wire burn-up.

Regardless, your circuit now appears to be dead, possibly because that metal fatigue cracked a wire, making a hotspot that burnt up.

The "50 volt" reading is phantom voltage picked up capacitively from the nearby hot. The wire is disconnected and floating. The 50V doesn't have enough strength to do useful work, not even move a mechanical meter movement in an old school voltmeter. (cheapie DVMs are sensitive enough).

What to do

It's time to replace the cable with a proper 10/3+ground cable, then replace the socket with a NEMA 14-30, and replace the plug if needed. You might find a ground wire inside the box, but the hokey-jokey arrangement with the oddball wire must not continue!


It happens all the time that someone acquires a used dryer (or buys from a lazy appliance store) that has a 3-prong plug, but their socket is 4-prong. No big deal, it's easy to swap a cord to 4-prong. But something possesses them to change the socket to an obsolete type. Maybe they fondly remember being shocked by their dryer in their youth. Maybe the socket was $2 cheaper than the cord?

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