What is the reason for wiring a receptacle this way?
There are two cables on different circuits, and each cable has a white, a black, and a red wire (but no ground wire). The hot wires are black in one cable and white in the other. The tabs between screws are intact.
Janet
Replies
They're "daisy-chaining" the
They're "daisy-chaining" the circuit. Power comes in on one cable and feeds out on the other cable (to the next outlet in the string). The receptacle terminals are used as a convenient way to tie the two cables together (though wire-nutting them together is preferred).
Two circuits?
Was it necessary to use two circuits? Wouldn't one circuit do for all the downstream outlets?
Also, one of the hot wires is white, instead of black, and it is attached to a silver screw instead of a brass one. Is this okay?
Janet
Two sources, then?
I used a voltage tester on each of the wires. The black hot wire seems to be on a different circuit than the white hot wire.
Janet
If you test between the black and white wires you should see full voltage. If you test black wire to ground you should see full voltage. If you test white wire to ground you should see essentially no voltage.
What you have is in essence a single continuous cable that has been cut so that the receptacle could be inserted. The cut ends of the wire were joined using the receptacle screws, making it electrically a single continuous cable again.
Note that a "circuit" is two wires (not counting ground). The "hot" (black) "goes out to" the device on the other end while the "neutral" (black) "comes back from" the device. You need both a black AND a white wire to "complete the circuit", so that electricity can go around in a circle through the device on the other end.
Here is how it's wired:
View Image
How to tell the number of cables?
Maybe I'm misinterpreting what happened:
I plugged a lamp into the receptacle and started turning off circuit breakers, stopping when the lamp turned off.
When I pulled the receptacle out of the wall, I saw that one brass screw was loose, and its wire (white, for some reason) jiggled and gave off sparks. So, I used the voltage detector to test the wires.
The loose white wire made the voltage detector glow brightly when tested against the box and one of the blacks. (The detector gave off a faint glow when that same white was tested against the remaining black).
So, I went back to the panel and turned off more circuit breakers until the voltage detector stopped glowing altogether.
Does this mean the box is on two different circuits—and what is the point of wiring it this way?
Janet
That looks like a multiwire circuit.
The white is the commoin neutral, the black is on one phase and the red is on the other.
Either a red/white or black/white combination would get you 120v and red/black would be 240.
I see two violations according to current code.
The white is depending on a device for continuity. It should be joined under a wirenut and a separate wire coming out to the receptacle so removing the receptacle does not break that circuit
At the panel, the two breakers should be tied together, so tripping one, opens both sides of this circuit.
Earlier versions of the code did not have either rule.
Be careful and be sure you have BOTH breakers off before you do anything with this and I would identify them, even if you are not ready to group and tie them. I would do the latter
I just made an expensive mistake :(
I replaced the receptacle with one that wasn't old and painted over (why does anybody paint an outlet?). The only change I made to the wiring was to move the white wire to a brass screw, because the books say that hot wires go to brass. It seemed to work; lamps plugged into the outlet work just fine.
Then I went off to do a load of laundry. The washer ran less than a minute before abruptly shutting off, popping two circuit breakers. Yes, those two circuit breakers in a different part of the house. After resetting the breakers, the lamps still work but the washer will not turn on. The voltage tester lights up when plugged into the outlet for the washer, so I guess the washer is broken.
This can't be a coincidence. Did I break the washing machine just by moving the white wire to a different screw?
Janet
The white wire is NOT "hot"
The white wire is NOT "hot" (or at least not supposed to be). Unless it's been remarked (with the end painted or at least a bit of tape wrapped around the insulation) it should not be "hot".
I think at this stage you need to get an electrician, or at least a friend who knows something about electricity -- moving wires around like that is very dangerous.
(And get rid of that neon tester and, if you plan to continue with this, get a decent voltmeter or vibrating voltage tester.)
If this is a multiwire circuit and you open up the white (neutral) the side towards the load is certainly hot. You might also start seeing things letting out the magic smoke since the circuit is unbalanced.
I can't even guess what was done when these circuits were wired. People do all sorts of crazy things when they're wiring.
I'm also of the opinion that it's time to call in a professional. If you can't bring yourself to do that, you're going to have to trace the circuits back to the breaker panel and start from the beginning.
Oh, that's a given. A service call for the washer comes first, though. I can do without lamps in the dining room, but a washing machine is an absolute necessity!
Janet
Greg,
I didn't understand the half of what you said, but it sounded right, esp. when you mentioned "240V". The cables in this box have 12-gauge wire, while the other receptacles I've replaced were connected to 14-gauge wires. At the time, it didn't occur to me that the heavier wire might mean different handling (other than it was more difficult to cram the wires back into the box).
Janet
The size of the wire really does not say much about the voltage you may have in the box.
In the case of a multiwire circuit (AKA edison or shared neutral circuit) you are essentially getting two circuits out of 3 wires, sharing the white between them.
When I see a red wire in a box, it generally assume it is either a switched leg or I am looking at a multiwire circuit.
The fact that you had to turn off 2 breakers to drop power somewhat confirms this. The only way to really confirm this would be to check the voltage from black to red with a meter or to look in the panel to see if one of the two breakers has a red wire on it. (going into a cable with the black on the other breaker)
These breakers should be right next to each other and have a handle tie between them but that was not always true in the code.
Most likely you were just seeing "phantom" voltage. The typical neon tester needs only about 50 volts and very, very little current to glow dimly, and will do so just due to 'capacitance" between adjacent wires, etc. Reliably testing with a neon tester actually requires more skill than using a regular voltmeter.
Everything back in place
Thanks, Dan. I put the white wire back the way it was, and put in a service call for the washer.
The sad thing is, the damage wasn't the result of a complicated or ambitious project. My goals were to a) create a circuit map for the panel, and b) replace any damaged, painted, or two-prong receptacles.
Well, let's hope that pushing a button will fix the washer (although it will still cost $249 for the repairman to do that).
Janet