Why are hot legs to neutral of a 240 volt circuit reading different values?

Question

I bought a new dryer today and upon plugging it in it wouldn't turn on. I tested the wires on the terminal block with a multimeter and one of the hot legs to the neutral wire reads 240 volts and the other hot leg to neutral reads 0 volts. As I understand it both of these should instead read 120 volts.

I swapped out the power cord for the power cord from my old dryer which worked perfectly fine and got the same readings, so I believe it is an issue with the terminal block itself. The dryer was discounted due to "repaired control board" so is it possible that the repair was not properly done? Does anyone have any idea what might cause this and how I can fix it?

Below is a picture link showing all of the multimeter readings I took.

Answer 1

Based on the picture and description, the only thing that makes sense is a short between white (neutral) and black (hot 1). There are a few different possible places for the problem:

• Receptacle
• Plug
• Inside the dryer

I would start with the receptacle. Unplug the cord. Check readings between each pair of the 4 conductors in the receptacle. If you get the same problem (neutral to one of the hots is 0 and to the other hot 240, and neutral to ground 120) then the problem is either in the receptacle or in the panel.

If the receptacle checks out OK then:

• Disconnect the cord from the dryer.
• Check continuity of each wire (the bare lead) to each prong on the plug. Each should show continuity only between the wire and one prong, and no continuity between wires or between prongs. If there is a problem, return it (or toss it) and get a new cord/plug.
• If it checks out OK, then check continuity on the dryer between black and white screws. If it shows continuity, the problem is inside the dryer, and since it is a new dryer that should be a warranty repair.* If it does not show continuity then this is a bit of a mystery.

* Just saw the part about "repaired control board." Depending on specifics, even with a repair there should be a warranty, though it might 30 days rather than the full regular warranty (typically 90 days or 1 year). The problem could be something extremely simple such as a wire connected to the wrong location on the control board, or it could be a major problem such as another bad control board. I'd be a little concerned because the standard procedure for replacing a control board should include testing heater, motor, fan, etc. which would have shown the problem.

Answer 2

Sounds like a Lost Neutral to me.

I think the neutral wire in your wall is broken or disconnected, either inside the junction box, or inside the service panel.

Checking voltage at the socket would settle this question. Expect weird voltages on the neutral wire because of "phantom voltage".

The timer and tumble motor is 120V and is wired between a phase and neutral, so if neutral isn't connected, the timer and tumbler can't run, and it pulls neutral to phase voltage.

This same problem would have prevented the old dryer from working.

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The most common failure point is a loose connection at the socket terminal or neutral bar, potentially causing arcing. Given the probability of arcing already having happened, you should disassemble the wire connection and inspect both the wire and the terminal for charring or pitting. Since this is often caused by incorrect torque on the terminals, NEC now requires torque wrenches to be used to set torques (the new requirement is for small terminals - large terminals always had this).

Your cable needs to have a cable clamp where it enters that round knockout, and it needs to clamp the cable jacket. As it is now is a code violation, can't just stick cables through knockouts.

Answer 3

There is clearly a problem with the neutral connection, there is no other reasonably plausible scenario that could cause the readings you are seeing.

So why do you get good voltage readings when testing at the socket? A possible explanation is that, while bad, the neutral is not entirely open circuit. A connection in the tens or hundreds of kilohms will produce voltage readings that look fine when tested with a typical 10 megohm multimeter but as soon as you put a non-negligible load on it the load "wins".

So why did your old drier work? My best guess is that someone forgot to disconnect the neutral to ground bonding strap. So the Ground was acting as a bootleg neutral.

Either way you need to find the bad neutral. Turn off the power and measure resistance between neutral and ground. If things are working correctly the resistance should be very low. Things aren't working correctly in your case though so I would expect you will find a high resistance. Work through the circuit until you find the fault.