Came across the following wiring at a friend’s house today: Standard duplex outlet box with 2 pairs of wires. Each pair has a black and white wire. Pair #1 is controlled by one breaker. Pair #2 is controlled by a dual pole breaker. Duplex outlet is wired with both white wires together on the neutral slot, and both black wires together for the hot slot. Here’s the confusing part: When measuring voltage using a multimeter (so it’s high impedance):
Pair#1 Blk to Gnd = 125V
Pair#1 Blk to Wht = 125V
Pair#2 Blk to Gnd = 125V
Pair#2 Wht to Gnd = 125V
Pair#1 Wht to Pair#2 Wht = 125V
Pair#1 Wht to Pair#2 Blk = 125V
I don’t remember what Pair#2 Blk to Pair#2 Wht measured. I think it was zero.
Questions:
1. How come tying the 2 Wht wires together didn’t cause a short? Was the 125V measured across them just due to the meter’s high impedance?
2. Why are 2 lines controlled by 2 breakers tied together at the outlet? Is this safe?
3. Are the 2 pairs different phases?
By the way, I’m sure the outlet wasn’t split.
Replies
Pair#1 Blk to Gnd = 125V
Pair#1 Blk to Wht = 125V
Pair#2 Blk to Gnd = 125V
Pair#1 Wht to Pair#2 Blk = 125V
I'm no electrician ......but this looks normal.
It's this one that looks off...Pair#1 Wht to Pair#2 Wht = 125V"If all women are crazy...I married their Queen!!!!"
Edited 6/17/2008 12:54 am ET by jet
Stan,
It'd help to have some more information.
It's essential to make three voltage measurements for each cable:
--black to white,
--black to ground, and,
--white to ground.
When voltage is zero, measure resistance.
Also, make these measurements between the conductors of the two cables:
black #1 to black #2, white #1 to white #2, and ground #1 to ground #2. Again, if there's no voltage, measure resistance.
And yes, using a low impedance tester will give you better info. One way to do this without spending the $ for another tester, is to put a 40 watt incandescent light bulb across the wires. If it lights up, you've got voltage. If it doesn't light up, but you measured some voltage across the two wires, it's ghost voltage.
This could be several things, but I can't make sense of what's going on unless I have the other measurements.
You might check out this issue of FH for some recommendations on voltage testers for electrical work.
Work safe,
Cliff
Unfortunately I won't have the chance to do any more measurements. My friend asked me to replace the outlet, which had cracked and blew the breaker every time someone plugged something in. I ended up putting in a new one wired exactly as the old and everything worked fine. I don't think he'll let me take everything apart at this point. Based on the fact that tying the 2 WHT wires together ended up ok, I have to assume no current flows between them, so maybe it was a ghost voltage picked up by the multimeter. Any idea what might be the intention of this setup? I found it odd that 2 seemingly separate lines controlled by different breakers got tied together in an outlet.
Here's more detail: I removed the BLK wires from the outlet first. As I removed one of the WHT wires, I noticed a small spark. I then suspected it was a split outlet driven by 2 circuits. So before I touched anything, I started measuring for voltage even though he had turned off the breaker (this was the breaker that tripped when the outlet was used). That's when I found the 120V still present and sent him back to the basement. We were on cell phones as he tried all the remaining breakers and ended up finding that a second double pole breaker controlled the other BLK/WHT pair. Good thing - I don't look good with curly hair...
When the new outlet was wired in, everything measured fine. Something about disconnecting the 2 WHT wires made the "extra" voltage appear.
Any ideas? At this point I'm just trying to understand this setup (and whether it's safe).
Dead end one set of the b+w and cap off. Just use one live.
Both lines are on the same side of the panel feed.(120 of the 240)
W to W=120 ? hmmmm that one needs more testing but if dead ended in the box and capped oh well.
Thinking more ? double pole breaker Is it a miss labeled W that's hot? coming out of the panel.
But why not shorting unless duplex is separated? carrying for a ? Window AC?
Somebody replaced with wrong receptacle and tried to force plug and mismatch broke it.?????????????????
Safety first and when you put your finger print on it you are now responsible.
Stan,
You're a lucky guy, ja.
I once worked on a circuit that was fed by two breakers, just like yours, and just like you I didn't realize it intil I was almost done. I felt stupid but also felt good that my techhique was clean, that is, I hadn't touched any of the bare conductors while doing the work. The dual-fed situation revealed itself when the hot lead touched a steel j-box and sparked. I was suprised (I was going to say shocked, and I guess that would be right, figuratively), and recoiled away, almost driving my scalp into the bed of nails coming out of the roof sheathing (this was attic work).
Live and learn. That's when I decided to always follow the protocol for checking for voltage that I describe in the article in the current issue...
Anyway, it seems that the circuit which you worked on is fed by two breakers, both on the same pole or leg of the supply. Given that one of them originiates from a two-pole or handle-tied breaker, it's probably a multi-wire (shared neutral) circuit. When you disconnected the white wire that sparked, you were interrupting the return current on the multi-wire circuit. That's confirmed if you disconnected the hots first, and the neutrals sparked when they were disconnected. Do you remember?
The dual-fed receptacle situation is not good. It works, but things could get very dangerous if comething changes--like an interrupted neutral on the multiwire circuit, or someone moving the non-multiwire hot to another breaker (different pole).
I'd have the friend get a licensed electrician or electrical contractor to fix the situation and check the wiring for other land mines. You may be doing this unpaid and as a favor, and as you're not a qualified person, but you still have a moral obligation and probably legal liability to not allow a potentially dangerous situation to remain.
I'd suggest that you advise your friend to shut off the power to both circuits until a sparky can dissect it and make it safe. At the very least, shut off the power at one the breakers (the possible multi-wire one would be my chioce), then have an electrician make it right.
Work safe,
Cliff
"When you disconnected the white wire that sparked, you were interrupting the return current on the multi-wire circuit. That's confirmed if you disconnected the hots first, and the neutrals sparked when they were disconnected. Do you remember?"Yes, Cliff, that's what happened, so it must be a shared neutral situation. I appreciate both the explanation and the advice. I'll have him turn off the double breaker and get an electrician to fix this. Someone else posted a suggestion to cap one circuit and run the outlet from the other. Do you agree? What would that do to the other (double pole breaker) circuit?By the way, what would the fix to something like this be (don't worry, I'll leave it for the pro) and why was it done like this to begin with (I assume by a licensed electrician)?
Stan,
You're welcome.
I'm thinking it wasn't done by a qualified, competent pro. Anyone can make an occasional mistake, but feeding a receptacle from two circuits is not a simple, inadvertant goof--like reversing polarity when you're brain dead or in a hurry. And a good sparky checks and re-checks his or her work, and tests it to verify it's right, before calling the job done, to catch the rare mistake.
Yes, the simplest fix would be to disconnect one of the supply conductors and cap it off in the receptacle box. And see what, if anything, loses power. If everything still works, the hazard is reduced, but that doesn't resolve the mis-wiring issue. Someone will have to deal with it eventually. Capping off one lead of the multiwire may have no other effect, but it's hard to say. If the circuit is heavily loaded, and is now being fed by one breaker only, the breaker may trip. That's a good thing.
The electrician ought to check the neutrals for these two circuits in the panel to make sure they don't show signs of overloading/overheating. Sometimes a dual fed receptacle has two supply leads and only one good neutral. Sometimes one of the neutrals has a poor connection with high impedance, and the other carries the lions share of the return current and overheats--sometimes in the panel and sometimes at a poor joint (splice or termination). Using a voltage drop tester like the Ideal Sure-Test or the Tasco Inspector III is a good way to chase down a bad connection. If the electrician has either of these testers and knows how to use it, he or she probably is the right person for a troubleshooting job like this.
The point is not just to get the thing working (which you've done) or even reduce the risk by eliminating the dual feed. You've got to make sure the wiring is safe.
Cliff
Thanks, I'll pass your recommendation along. I'm sure my friend will do the right thing. Fortunately, he's pretty terrified of electricity (that's how I got involved). Nothing worse than someone who doesn't respect the potential danger of something they feel is so commonplace.For me, this was a great lesson. I've downloaded a ton of articles on shared neutrals and now understand the issue better. From what I've read, the big motivation for doing this was to save a little wire. Talk about "penny wise and dollar foolish..."Thanks for your thoughtful, expert advice.