An island in my kitchen has two circuits - one for the GFCI outlets and one for the dishwasher. There is one 12/3 cable coming out of the slab. When I turn on either the breaker for the outlets or the breaker for the dishwasher both the red and black wires go hot. Is the 12/3 wired wrong at the breaker box? Thanks for any help.
Jim
Two circuits run with the one cable.
R
Hi, You have a short or partial short down stream from breaker. Use multi-meter for trouble-shooting
How would a meter find it?
Doesn't he have to visually examine the cable looking for where the short is, and then open the cable and separate the black and red.
Or do the whole cable like that until he gets to the part where the short is? Then a meter would verify it, but it would be mostly the looking at it and the splitting open.
Was it working ok before and then suddenly went bad or was it bad from the time it was wired? Most shorts are near the ends and due to sloppy work. Unusual for a good cable to suddenly go bad somewhere in the middle unless someone drove a nail through it or a rat got to it.
Bob
Are you using a meter to test these wires? If you are, stop and use a pigtail socket and a light bulb. You may be getting a false reading from the meter.
Is there 120 or 240 across the red and black?
Has anything been changed recently such as an outlet replaced?
You have a shared neutral circuit. usually these types of circuits are used on the dishwasher and disposal and normally the kitchen outlets would have their own circuit(s). If you replace an outlet on this type of circuit then you must remember to break off the tab between the 2 screws on the hot side.
At the panel both breakers should be next to each other and they should have the handles tied together with some sort of clip. When both breakers are on then you should measure 240V between the red and black. If they are not like this then the neutral (white) could get overloaded.
Kevin
"Is the 12/3 wired wrong at the breaker box? Thanks for any help. "
That should be easy to determine by inspection. If the cable is a homerun straight to the kitchen, the most likely problems would be on either end. It's possible a nail or similar was driven into the cable somewhere along the way, but less likely.
Another key question. Apparently there is a GFCI breaker for one hot, none for the other. Yet you have two hots, one for the dishwasher, one for the outlets and just one neutral? This makes no sense, as the GFCI can only work by comparing the current on the hot to the current on the neutral. If the neutral was shared with another hot, then there would be a current imbalance and the GFCI would always trip with the dishwasher plus any load in one of the outlets. Something ain't right here and may be the root of your problem.
trad said: This makes no sense, as the GFCI can only work by comparing the current on the hot to the current on the neutral.
Ray asked: If the above is correct then why does a GFCI trip when you jump out the nuetral and the ground?
Is it ok to use 3 wire in this way?
I wouldn't think it is safe to connect 3 wire to the breaker box using two breakers next to each other. As you said, you would end up with
240V potential at the end of the wire (pretty dangerous for the next guy). I always run wires using a separate breaker for each piece of wire(romex) unless it is a 240V circuit for range, AC, etc. The only time I use 3 wire is for a 3 way switch circuit, ceiling fan or something of that nature. Of course I'm not a licensed electrician, just weekend warrior with a cool tool pouch.
By the above, I meant that for the GFCI to function, it has to be able to compare the current flow on the hot to the current flow on the neutral. That is exactly what it does and it will trip if they are not equal. Hence, you can't have a GFCI share a neutral with another circuit, which, if I understood it correctly, is what the OP says he has.
GFCI's will also trip, as you pointed out, if the neutral and ground are shorted, even without a load. They do that because they inject a very small test current that they generate onto the hot and neutral. If everything is proper downstream, then with no load connected, these currents don't go anywhere. Short the neutral to ground, and then some of the neutral current will return via the ground path, resulting in an imbalance and trip, even with no load.
Absolutely. As long as it's done properly, that is.
You end up with 240V between the red and black, yes, but so what? It's no more dangerous than a 240V circuit for a stove or a dryer.
And, in fact, it's *very* dangerous to *not* do it that way. If two circuits share a neutral, the two hot wires *must* be on opposite legs of the 240V service, and have a 240V potential between them. That way, the current in the neutral wire is the *difference* of the currents in the two hot wires (e.g.
12A on the red wire and 17A on the black means 5A on the neutral). If, instead, you put the two hot wires on the same leg of the service, the potential between them is 0V and the current in the neutral wire is the *sum* of the currents in the two hot wires: 12A on the red wire and 17A on the black means 29A on the neutral, which overloads it and may cause a fire.Google on "Edison circuit" for more information.
For this application, you should use a 240V breaker also. That way, throwing one breaker disconnects both hot legs simultaneously.
Good info. Thanks.
I'm with Ray on this one. I think it is considerably more dangerous than a 240V circuit for a stove or dryer. If you're working on a circuit for a dryer or stove, one would expect there to be 240V between two hots. But if I happen to be working on a std outlet, most people would never expect there to be 240V between the two hots. For example, I could see someone having things opened up for testing, and allowing the two hots to touch each other, thinking they would be on the same phase, which in every case that I have seen, they are.
Not saying you can;t do this, but anytime you start to deviate from what is common or expected, you have to ask, is it worth it, just to save another neutral run?
Good discussion. As for OP's question, I'm wondering in addition to Kevin's suggestion of replaced outlet, if fixture or switch was replaced and red and black wire nutted together. But this would imply both are on same phase with previously noted overloaded neutral. Maybe this island was a renovation, with wiring by non-electrician?
Seems to me it is "common" and should be "expected". Looks like an argument for calling an electrician.
If this is on 2 phases and 240V between hots I hope the comments of John Grabowski weren't missed - test with a light bulb. A hot-to-hot short would trip the breakers. If on the same phases - 120V between hots - it is connected wrong and the neutral can overload.
bud--
Bud and John are on track. You can't reliably check voltage on an "open" wire with a digital meter, If that wire is floating on both ends (open breaker) it will pick up enough stray voltage from being near the hot wire to trick a digital meter. Any tiny load will make that go away.
As for the 3 wire circuit. The only way that will work is if you do have 240v between the hots. That way the current in the white cancels. Otherwise it adds and you burn the white up. The safest way is to have it on a 2 pole breaker or use handle ties.
Zero volts between hots would be closer.
bud--
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