220 line for an electric dryer

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Old 02-17-11, 09:03 AM
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220 line for an electric dryer

Hello:
I need some help from the experts. I have a rental property with a new tenant. When I rehabbed the house I ran 10/3 + G for the dryer circuit, and installed a 4 prong receptacle. When the tenant moved in, they brought an older dryer with a 3 prong male plug. They called to ask if I could change the receptacle.

Since I was on vacation, I called my electrician to go there and make the change. When I got back, I went tothe property to look at his job, and noticed what I think is a possibly dangerous mis-wiring. When he made the change, he tied the neutral white wire and the ground wire together under one terminal. Forget that there are two wires under one screw (I KNOW that is wrong, but could correct that with a pigtail). However, it seems to me that the ground wire should NOT have been connected to the neutral, since, as I understand it, that would cause current to be going over the ground wire. Can any of you shed some light on this for me?

Thanks.
 
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Old 02-17-11, 09:42 AM
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The receptacle should have been left four-wire as that is the safer version and is required by modern code. The correct fix is to replace the cord on the dryer with a four-prong version (NEMA 14-30P) to match the receptacle.

When the cord is replaced, it also requires that the bonding strap inside the dryer, which connects the frame to the neutral terminal, be disconnected. Different manufacturers do the strap differently so examine the dryer or consult the manual for exactly how to disconnect it. The black-white-red wires from the dryer cord go to the terminal block (usually in that order), and the green goes to the grounding screw on the chassis. If the cord is hooked up correctly, you should be able to set your multimeter to "continuity" mode, and test between the "L" shaped prong and the round prong and read no continuity (infinity ohms). The test should be done with the dryer unplugged.
 
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Old 02-17-11, 09:52 AM
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ibpooks:
Thanks for the quick reply. I understand what you are saying. However, just for education purposes, isn't it incorrect to connect the ground and the neutral? Does that connection pose a potentially dangerous situation? Thanks.
 
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Old 02-17-11, 11:47 AM
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Yes it is incorrect because it sends current through the ground wire. Though it's often harmless, in some circumstances that can lead to a hazardous voltage level on exposed metal surfaces like plumbing fixtures or metal appliance frames. This type of connection used to be legal for dryers and ranges up until the 1996 code so you will see the old three wire connection in homes built before that code or on second-hand appliances.
 
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Old 02-17-11, 12:04 PM
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Thanks. I did not know this was ever allowed. Let me ask one more question... If, with the neutral and ground connected together, the bare ground wire went into a junction box (metal) and touched that box, wouldn't that box have current traveling through it when the dryer is drawing current? If someone touched that juntion box while standing on a damp concrete floor, couldn't they get shocked with that wiring? If so, I don't understand why it was ever legal to do that.

Thanks for your help.
 
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Old 02-17-11, 12:26 PM
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Originally Posted by JMattero View Post
wouldn't that box have current traveling through it when the dryer is drawing current?
Yes.

If someone touched that juntion box while standing on a damp concrete floor, couldn't they get shocked with that wiring?
Yes they could be shocked. A harmful shock is not likely unless the ground and/or neutral wire is also compromised between the dryer and main panel, but shock is possible even with an intact wire.

If so, I don't understand why it was ever legal to do that.
The legend is that it was a concession to save copper wire for the war effort during WWII, and for whatever political/bureaucratic reasons was not rescinded until the 1990s. Perhaps someone with a good grasp of the code history knows for sure.
 
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Old 02-17-11, 01:57 PM
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JM just a suggestion, it might be time to look for a new electrician. If he does this on basic stuf he should know ....well you see my point.
 
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Old 02-17-11, 02:04 PM
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Ray;
Point well taken! I thought the same thing whenI saw what he did. I am NOT an electrician, but do plenty of electrical work, and I would not have done it that way. However, I wanted to make sure that my thought process was correct before I told him about it. Thanks.
 
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Old 02-17-11, 05:12 PM
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Originally Posted by JMattero View Post
Thanks. I did not know this was ever allowed. Let me ask one more question... If, with the neutral and ground connected together, the bare ground wire went into a junction box (metal) and touched that box, wouldn't that box have current traveling through it when the dryer is drawing current? If someone touched that juntion box while standing on a damp concrete floor, couldn't they get shocked with that wiring? If so, I don't understand why it was ever legal to do that.
Thanks for your help.
If this had been done properly to pre 1996 codes, the neutral and ground in the appliance would have been bonded together and the ground wire in the romex wouldn't have been used at all. Back then, the grounding was allowed to be through the insulated neutral conductor. Never has a bare ground wire been allowed to be used as a branch neutral conductor to my knowledge.
 
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Old 02-18-11, 06:10 AM
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Joe:
Thanks for the reply. One more thing... with a 3 prong receptacle, and 10/3 + G wire, would it not be best to connect the bare ground to the metal on the receptacle? To me that would be better than not using the ground at all.
 
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Old 02-18-11, 07:53 AM
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Best is to reinstall the 4 wire plug and inform the tenant it is their responsibility to have the cord set correctly changed on their dryer. I say correctly because we have had reports here of the neutral bonding strap not being removed when a 4 wire cord set is installed.

Maybe time to add a clause about tenant provided appliances to the lease.
 
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