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Alternatives to completely re-wiring a 3-conductor 240V circuit?

Alternatives to completely re-wiring a 3-conductor 240V circuit?

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  #1  
Old 07-24-05, 12:16 PM
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Alternatives to completely re-wiring a 3-conductor 240V circuit?

I've seen on this discussion group that using a neutral for a ground (3 conductors) in 240 V appliances (such as dryers and stoves) is not good. (This is why they must all be 4 conductor with ground now.) Ok, so I live in a 1985 house that has wiring for only 3 conductors to the dryer and stove.

Is there anything that you can do to improve the safety of this kind of wiring without completely re-wiring the circuit from scratch? I realize that a complete re-wire is probably best however, I just don't have time (to do it myself) nor funds (to pay an electrician) to do this now (small babies in the house ). (If I did it myself, I'd either have to drill lots of holes to run new wire, or remove the existing wire and put new wire in its place and my wife couldn't live without a stove or dryer for a week or two while I put in 10 minutes here and there to get this job done.)

While checking my dryer connections the other day, I noticed that in some locations something called a "dedicated ground" might be an option. Instead of grounding the metal dryer shell to the neutral wire, it can be grounded through a 4th conductor that is separate from the power cable but connected to a proper ground elsewhere (such as a metal water pipe if your house has that kind of grounding).

So can any of your electrical gurus out there tell me (assuming that this kind of connection is permitted in my area) would adding a 4th conductor ground to an existing 3-conductor 240V circuit be better than just the 3-conductor circuit? Or is it worse? Is it even worth doing something like this? How "bad" are 3-conductor 240V circuits? Is this an "all or nothing" kind of fix proposition?

My home does have copper water pipes however, the electrical system is not grounded to them so if I were to add a separate ground, I would probably need to run a 4th conductor across the basement to the grounding wire of the electrical panel.

If this is an option, can the 4th conductor ground wire be green THHN/THWN that is run in parallel to and cable tied to the existing wire from the dryer to the panel? And then, could the plug and dryer cable be switched to 4 conductor or must the green ground wire be only connected to the dryer grounding screw? (removing the neutral ground of course).

The advantage to me doing it as a retrofit instead of a replacement is that it can be done in short periods of time over a long time, at low cost, with almost no interruption in service. It also means that I don't need to go in the electrical panel... something I've done before, but because I know how dangerous electricity is, I try not to do.

If this isn't something that people advise or is possible and still be within code, these appliances will probably remain 3-conductor for the next 50 or so years. :-) I want to do whatever is prudent and reasonable to provide as much safety as possible.
 
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  #2  
Old 07-24-05, 12:53 PM
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Yes, you are allowed to add the fourth conductor back to the main panel. But you will need to open up the panel to feed the new grounding wire in and connect it. For an inexperienced person, that danger might be greater than living with what you have.
 
  #3  
Old 07-24-05, 12:56 PM
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The 240V appliances you discuss do not use the neutral as the ground, it is the otherway arround. The appliance is virtually all 240V, no neutral needed. The only neutral current on these appliances is possibly a clock and light for a stove and possibly the motor and timer on the dryer. i.e. virtually no neutral current. The small added benifit of saftey gained by rewiring would not, in my opinion, be worth the effort. If something goes wrong with the wiring in the future, then it would be required to upgrade the the 4 wire solution. But for now, I wouldn't loose sleep over the current situation.
 
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Old 07-24-05, 04:48 PM
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Scott, it is actually the other way around. The ground in the appliances is bonded to the neutral. This is why the white wire MUST be a white wire (or SE cable). These are 120/240 ungrounded circuits.
Basically dryers and ranges(ovens, stoves) are the only appliances which can do this.

jbmdharris,
I would not worry about this at all, but if you are going to lose sleep over it I would all but guarantee that a circuit run in 1985 will have a ground wire, it is just not being used. You may be able to simply replace the receptacle and cord with 4-wire parts.
Can you describe the cable run to the appliance receptacle? Tell us what it says on the sheathing.
 
  #5  
Old 07-24-05, 06:08 PM
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I never thought to actually check the cable... I just assumed the cable would match whatever the plug needed. The cable to the dryer is NM-B 10/3, so that means there is a ground wire present, right? It would be a simple matter of verifying that the ground is in tact, switching the outlet, and then switching the cable on the dryer. I've even got the right cable for the dryer. I just need a new outlet.

I guess the next thing to check is the stove. I haven't actually found that wire yet. What I thought was the stove had 12/2 with ground stamped on it. Clearly, that's not the stove.
 
  #6  
Old 07-25-05, 06:15 AM
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Assuming you find a ground wire when you open up the box for the dryer receptical, be sure to check the panel box and make sure the ground wire is connected there.

I wish I had been that lucky...My 1975 dryer circuit is 10-3 with NO ground wire. I just ran a new 10-3wg for mine (was moving dryer in a remodel).
 
  #7  
Old 07-25-05, 07:18 AM
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It is permissible o Ground the frames of cooking-appliances and dryers to the Neutral if these conditions are satisfied;

This is an EXISTING Banch-Circuit.

The supply is single-phase, 3-wire, 120/240 volts.

The Neutral is #10 or larger ( copper).

The Neutral is an insulated conductor, or, if un-isulated, the Wiring Method is type SE cable extended from the Service-panel.
 
  #8  
Old 07-26-05, 02:05 PM
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Wow, I learn something new everyday. I guess that I have seen people run dryers with 10/2 and tape the white to indicate hot and then use the bare for the ground (really neutral). I guess that this was very wrong . Thanks for the correction, I will add this to my not so vast quantity of knowledge. Thanks!
 
  #9  
Old 07-26-05, 02:33 PM
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Originally Posted by scott e.
Wow, I learn something new everyday. I guess that I have seen people run dryers with 10/2 and tape the white to indicate hot and then use the bare for the ground (really neutral). I guess that this was very wrong . Thanks for the correction, I will add this to my not so vast quantity of knowledge. Thanks!

After I moved in, I found someone had moved the old 3-wire dryer circuit (may or may not have been OK depending on how long ago they did it). They had installed the three prong receptical in one of those single gang metal boxes that you can take the sides off of and expand (TINY box). In addition to the 10-3 (without ground) romex coming in, there was a 10-2wg going out, supplying a 20A 220V receptical on the opposite side of the wall (for a heater, I assume). So that white neutral was attached to a bare "ground" wire for the 20A receptical on a 30A circuit, and this done in a TINY box. (Lets see, how many code violations there? Box fill, 20A rec. on 30A circuit, tapping off dryer circuit, tapping neutral for ground, and, if done after '96(?), modifying ungrounded appliance circuit).

Some day I am going to get around to writing up and posting all the violations I have found while remodeling our home. The home wasn't wired wrong to start, but a previous DIYer who lived there remedied that.
 
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