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I am in the military and came back from a month overseas and my 3 prong electric dryer would not start. I am an electronics technician (radios) so I am quite experiences with electronics and theory (although DC is my strength).

I checked all the routine no start issues, door switch, start switch and thermal resistor all have continuity when isolated. I checked voltages at the receptacle and on the distribution block of the dryer hot to hot-240V, neutral to hot A-118V, neutral to hot B-123V and nothing would happen when start was pressed. I hit start and tried to spun the drum, nothing. I ended up pulling the front panel completely off and removing the drum and checked that I have 118V on M4 of the motor switch. In order to check the motor I created a test cable from an extension cord and (cut the female end off and stripped the ends) and connected it to the dryer power distribution on the hot side that controls the motor (not the heater) and neutral then plugged it into a standard 120 wall outlet and the dryer started up like a champ so I knew the motor was good. I then plugged the original cable back in and tried to start it and it didnt work. I then opened the motor switch and the voltage all looked good. I then manually shorted the relay for heating circuit on the motor switch and and the coil heated up. I then ohmed out the timing switch and it was good.

I then opened the receptacle and put my multimeter probes on leg A and neutral, it read 118V and when I pressed the start button the it dropped to 0V and leg B was at 240V. I thought it could be a open neutral (although I dont have much experience with neutrals being a DC guy but I am familiar with electronic theory) so I connected my multimeter between the common (ground) pin on the door switch and the bare neutral wire on the service panel and it read 1.3 ohms so there is neutral connectivity throughout the circuit (I also verified that all grounds had connectivity with the neutral in the service panel).

I am now at a loss as to where to go next. I really don't have an idea of where to go next as every thing else in my apartment works as it should and I don't have the funds to hire an electrician or a repair man. Any help or suggestions would be greatly appreciated.

  • Should this be on Electrical Engineering? – Jim Garrison Sep 16 '16 at 14:19
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    @JimGarrison No. – topshot Sep 17 '16 at 0:30
  • Sounds like about all that is left is thermostat(s), thermal fuse(s) (though maybe that is what you meant by resistor) and the control board though I don't know if the drop of A and spike of B is standard. Could be open neutral but don't know how that would suddenly appear. I assume you get same readings at your breaker panel. – topshot Sep 17 '16 at 0:51
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That NEMA 10 dryer receptacle is a hazard all its own, and may be creating a hazard for you right now.

AC power, as implemented in the USA, has many tricky twists that DC people aren't really prepared for. Some are relevant here; I'll describe them.

I gather you know 240V AC power is supplied from a transformer with a center tap. The center tap is defined as "neutral". There is 120V between either phase and neutral. Neutral has one job: be the one and only current return (in DC parlance, negative, Vss, or ground) for 120V circuits.

AC power has a Safety Ground which is tied to earth via water pipe or driven ground rods, and is carried throughout the electrical wiring (except in older wiring). Safety Ground** has one job: to deflect faults away from humans. Ground is not a current return, except during ground fault conditions.

In theory, neutral might "float" above Earth Ground by several hundred or thousand volts, due to capacitive coupling or leakage in the supply transformer. This would be bad, so neutral is "pegged" to Earth/Safety Ground via a tie in the main service panel. This tie is only at the main panel: never in a sub-panel, junction box nor appliance. As a result, neutral is near earth, and any phase is no more than 120V above earth.

The tie has a beneficial side-effect - if a hot wire touches safety ground, it has a fat current path through the grounding system and the tie back to neutral. This completes the circuit, flows high current and trips the circuit breaker. (If a neutral faults to ground, not much happens, as the voltage difference quite small, being only the voltage drop in the wiring.)

Most dryers use 240V for the heating coils, and 120V for everything else. (120V controls are cheaper). So it needs split-phase 240V - both hots and the neutral.

If you've been counting, you know your 3-prong NEMA 10 is a pin shy of a ground. This is where true stupidity sets in. NFPA (the authors of the Electrical Code) compromised with dryer manufacturers -- reasoning that since dryers are rarely ever unplugged or moved, the receptacle isn't likely to fail. So they authorize tying neutral to ground, even though this is dangerous and would be illegal anywhere else. Sigh.

So if you lose/break/float a neutral anywhere between the dryer and the panel, the 120V loads will not have a return, and will "lift" neutral to the voltage of leg A. Voltages will measure 240/0/240 instead of 240/120/120. Since neutral is now "hot" and it's tied to chassis ground, the chassis of the machine is also "hot". This has killed people.

Which is your symptom.

I'd start by replacing that dangerous NEMA 10 with a modern NEMA 14 connector, which provides a fourth pin for ground. I'd also retrofit a NEMA 14 plug, and carefully separate neutral and ground on the dryer. Also carefully inspect the wires between the connector and the panel. Somewhere in here I think you have a faulty neutral.

It's also possible your neutral problem is between the panel and the supply, in which case it would affect everything served out of that panel... but I doubt it.


** Electrical Code purists may dislike my careful choice of words "Safety Ground". That is to convey that it isn't anything like Vss. If you really want to know their Legal Names as specified in the NEC, Neutral is "Grounded Conductor" and Ground is "Equipment Grounding Conductor". Say what!? Of course this invites massive confusion, and both are wrong: Neutral is not grounded (except at the main panel), and Ground is not a conductor! (in NEC parlance, only wires which flow current under normal conditions are conductors.) These are terms only their mother could love, and I suggest avoiding them like the plague.

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Look at the rest of the house and see if you have some lights dimmer or brighther than others. If you do call the utility company and have themcheck on their side for a bad or loose neutral I am going to say that either the dryer cord is bad or you have a bad neutral inside the main or sub panel. I just replaced a dryer cord for a friend thathad same problem Some houses have a main panel that runs straight from the meter. the hot wires come from meter into panel.

If that is your hook up then pull the main panel breaker or fuse. Then making sure you are not touching the wires feeding in check the neutral on your neutral bar as well as the neutral for your dryer If you have a meter then a panel under the meter that is your main and then another panel in or on the house this will be a sub panel Pull the breaker or fuse from the main and tighten the neutral on the bottom side . then go to the sub and do as previously stated If this does not solve your problem then it is possible the neutral is broken or loose on the utility company side

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