4 wire 120/240 circuit for dryer not working

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  #1  
Old 02-16-09, 06:44 PM
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4 wire 120/240 circuit for dryer not working

Two days ago we moved into a house built in 1981. Last night I replaced the 3 prong dryer plug with a 4 prong plug. The fuse box has a 2 circuit wire coming off a 30 Amp breaker with two breaker levers connected to act in unison. My wife used the dryer today and all was fine. I turned on the dryer this evening and it started and then gave a PF signal and went dead. I checked the plug and one of the hot leads was dead. I went to the fuse box and the two hot wires coming out fo the fuse for the dryer test out fine from the fuse and create a circuit with the bare cooper line going up into the same line. I have now unhooked the plug and the red hot wire creates a circuit with the white wire but will not create a circuit with the bare copper wire. At the fuse box it will create a circuit red to bare copper. The black hot wire does not create a circuit with either the white wire or the bare copper wire but will create a circuit at the fuse box. I am mystified.
 
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  #2  
Old 02-16-09, 07:23 PM
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Most homes wired in 1981 have a three-hole dryer receptacle. If yours does (or did), you are not allowed to change the receptacle to four-hole. And it's not safe either? Is this what you did?

If you have a dryer with a four-prong plug and a house with a three-hole receptacle, you have to change the former, not the latter. And when you do, be sure to follow the dryer installation instructions because you have to make a slight jumper modification on the dryer when you do so.

Don't do this wrong or your dryer will be unsafe.

Tell us more about why you are doing this project.
 
  #3  
Old 02-16-09, 07:57 PM
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Thanks for the advice. I did replace the 3 pronged w a 4 pronged. I will switch back.
 
  #4  
Old 02-17-09, 07:35 PM
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I replaced the four prong outlet with a three prong outlet and I replaced the cord to the dryer with the matching three pronged cord. Now the dryer will not turn on. I have a voltage tester and there is a circuit when I connect thered wire to the ground and when I connect the red wire to the black. I have checked the wirig of the outlet and the cord and I am certain they are wired together. Do you think I damaged the dryer? The interesting thing to me is that the wiring diagram in dryer's owners manual for 3 and 4 pronged appear to reslt in basically the same configuration with the neutral wire connected to the same terminal on the dryer and the red and black wires connected to the same terminals on the dryer. Why was using a four pronged outlet and plug such a bad idea?

Thanks for your help
 
  #5  
Old 02-17-09, 07:52 PM
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Regulations say you cant make a 3 prong a 4 prong.

However, my dad (electrician) basically wired our dryer outlet from 3 to 4 wire.

The wiring inside a 4 wire plug is 2 hot, 1 ground, and 1 neutral.

I think as long as your breaker and wiring is up to part to handle the amperage, you could make due with a 3 wire plug.
 
  #6  
Old 02-17-09, 08:35 PM
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Is circuit working properly

I wonder if there is a problem with the electrical circuit to my dryer. I followed the advice of John Nelson and reversed myself putting back in a 30A 125/240VAC; 3-pole 3 wire outlet. The wire in the junction box had four wires red, black, white and bare copper. The red wire is hot and I create a circuit with my voltage tester when connecting red to white. However, the black wire is not hot - it does not create a circuit when I connect it to any of the other wires.

I have tested the wires from the 30A double pole fuse labeled dryer and both red and black in the fuse box are hot. When I turn off the breaker the red line is no longer hot at the dryer outlet.

Based on my read of other postings, I believe the black wire should be hot. Is this correct?

Also can someone explain why there was a problem hooking up the four pronged outlet when I had a four wire line going into the junction box.

Thanks for any clarity on this issue.
F
 
  #7  
Old 02-18-09, 04:55 AM
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You can change the receptacle to a 4 wire if you have 4 wires however, you need to remove the bonding strap that's connecting neutral to ground on your dryer.

I think they were under the impression you had a 3 wire and changed it to a 4 wire receptacle.

At the dryer, are you actually testing for voltage on the wire at the receptacle or at the dryer?

I've seen where the female contacts on the receptacle have loosened and when you plug the dryer in, it doesn't make contact with the blade on the plug.

If you are checking voltage at the receptacle and you don't have it there but at the panel, then you may have a junction box somewhere that has lost connection.

One other small point, when checking for voltage on either end, test at the wires and the screws. I've had occasions where at the panel I was getting voltage on the screws but not on the wire due to a loose connection.
 
  #8  
Old 02-18-09, 07:03 AM
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The 3-wire/4-wire issue has everything to do with safety and nothing to do with why your dryer won't work.

Get a voltmeter. There are three holes in your receptacle. Test the voltage between each pair. There should be 240 volts between the two slanted slots and 120 volts between each slanted slot and the grounding hole.

Are there?

If not, repeat the test at the circuit breaker panel, testing between the two screws on the breaker and then between each screw and ground. You should have 240 volts between the two screws, and 120 volts from each screw to ground. Be very, very careful removing and reinstalling the panel cover, and while the panel is open.
 
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