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jbierman

06:14AM | 04/15/07
Member Since: 04/14/07
2 lifetime posts
Bvelectrical
I was replacing the plug for my washer and dryer. It is a 120V 20Amp plug. I turned off the circuit breaker and while I was unscrewing the outlet from the box, the light over me flickered. The plug was hooked up with the black, white and ground wires. I measured the lines and found the black wire to ground had 21VAC(??). The white to ground had no voltage. I also noticed that the circuit continues via another wire going out of the box.

Here is the layout of the wires.

I will call the wires incoming (the one I believe is going to the circuit breaker) and outgoing.

Incoming White - Plug

Incoming Black - Plug

Incoming Red - Outgoing Black

Outgoing White - Plug (Shared with Incoming White)

Incoming Ground - Outgoing Ground - Plug

When I unscrewed the connection for one of the white wires, I saw a tiny spark and the light went out in my laundry room. I know that light is on another circuit breaker. Well, at least when I turn off that other circuit breaker that light doesn't work.

If I turn off the circuit breaker for the laundry room light, the 21VAC goes away.

Is it possible that the since my washer/dryer isn't using 220, they are using the other 110 line to "help" another circuit?

Any idea on why I would get 21V AC on the line?

Do I need an electrician or should I just hook up the new plug the same way it was hooked up before?

Thanks,

Jeff

Billhart

10:07AM | 04/15/07
Member Since: 04/25/05
1915 lifetime posts
That is called a multi-wire circuit. It is perfectly legal, but there is one mistake make in your case.

There is a big debate about whether they should be used on residential wiring or not. The disadvantage is what you found. Confusion for people that later work on the circuit

You need to verify that the two breakers are in adjacent slots so that they are on oposite legs of the 240. That way the neutral only carries the different in currents. Not the sum.

The mistake that is in your case is that with a multi-wir circuit the neutral is never suppose to go through the device.

What you need to do is to wire nut the neutrals along with a pigtail. That pigtail connects to the receptacle neutral.

If yous was wired tht way there would not have been any problem if yuo removed the receptacle.

But it would also be help to put a piece of tap beside those two breakers and label them SHARED NEUTRAL to warn the next person.

jbierman

11:05AM | 04/15/07
Member Since: 04/14/07
2 lifetime posts
Thank you very much.

TimBonham

11:27PM | 04/15/07
Member Since: 01/09/07
197 lifetime posts
"Any idea on why I would get 21V AC on the line?"

You probably tested this after you had disassembled the outlet, and nothing was connected. This is called a 'no-load' situation, as there is no electrical load on the circuit. Many of the common, cheap testers do not read accurately on a no-load AC circuit. So most likely, the 21v AC reading was not an accurate reading.

--------

BillHart mentioned the disadvantages of such a multiwire circuit; here are the advantages for them:

- saves money; 1 3-wire cable vs. 2 2-wire cables, plus installation for only 1 cable vs. 2.

- more future flexibility. If you or some future homeowner want use a 220v dryer, all that it takes to convert this from 2 110v circuits to a 220v circuit is switching the outlet to a 220v type, and replacing the 2 circuit breakers with a double breaker. No running new wire at all.

Contractors often run this kind of wiring into laundry rooms, because they don't know what kind of dryer the eventual buyer will install.

joed

11:04AM | 04/16/07
Member Since: 09/17/02
524 lifetime posts
I would find the other breaker that is the red wire and if possible tie the two handle together so they both go off at the same time. You may need to move one of the breakers so that the two breakers are beside each other in the panel. If you do have to move one breaker, make sure you have 240 volts between the two breakers.
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