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.
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.
It was working before, but I am assuming that it was wired incorrectly
from the beginning. Right now we are in the middle of a kitchen
remodel, so I had to move a couple outlets. That's when I noticed that
both circuits were live even with only one breaker on. I am testing
the bare ends of the 12/3 at the cable sticking out of the wall, so I
don't see where any shorts would be, but I'll check for nails.
I was using a voltage detector before. Using the pigtail and light,
the GFI circuit breaker turns on the black and the dishwasher circuit
breaker turns on the red. 240 volts across the red and black; 120
volts across the red and neutral and the black and neutral. Thanks!
John Grabowski wrote:
"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.
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 above is correct then why does a GFCI trip when you jump out the
nuetral and the ground?
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
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.
Kitchen couter top duplex receptacles have two separate circuit feeding
each plug in. You have to break the link to separate those two
receptacles to be fed separately. Wonder if mistake is made here.
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.
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.
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.
Doug Miller (alphageek at milmac dot com)
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.
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