I have a 2 pole 20 amp breaker that I though went straight to my
washing machine in the garage, but upon tripping it I see my fridge
and a couple 20 amp 120v outlets in the kitchen go out too. I am
wondering if it is possible that someone has wired one side of the
breaker to go to the kitchen and one side to my washing machine. If
so, what would be the best way to tell? Thanks
Open up the panel and remove one wire from the breaker, then see what gets
turned on. Most likely you are correct, that the kitchen outlets and fridge
are on one wire, and the washer is on the other, as that would have been the
Nec legal way to do it.
For single phase AC, a "multiwire circuit" is a 3 conductor (plus EGC)
circuit in which there is a neutral and two hots on opposite legs.
Also called an Edison circuit or a shared neutral circuit.
As John and Wayne explained, these are circuits that share a common neutral.
There was only a requirement to use a double pole breaker if both circuits
were attached to devices in a single box, but it really is a much safer way
to wire them, and as John pointed out is required by the 2008 NEC
Thanks to both of you for the explanations. I have another question
If the gauge of the wire is appropriate for say 20 amps, and you supply
each wire designated for line from a separate 20A breaker, how can the
neutral wire be of adequate gauge for both circuits? In other words, if
20 amps were drawn on each of the line wires and the common neutral was
used for both circuits, wouldn't the capacity of the neutral be exceeded
and be over 20 amps?? Maybe I am missing something?
The current wave cancels out. So if you have say 6 amps draw on 1 wire
and 7 amps on the other, then the combined current on the neutral would
be only 1 amp. 20A and 20A = 0A etc... So the most amps the neutral will
see is 20A.
Thats why it's important to keep the 2 wires on opposite hot legs in the
panel. Using a double breaker assures that.
If both hots are put on the same leg then the neutral will be overloaded.
Not sure why it would matter?
On some double breakers you can take the connecting bar off. If not then
you would have to open the panel and disconnect one of the wires from
the breaker. Turn the beaker back on and map out the circuit. Then
change to the other wire....
It's possible that you have an 'Edison' circuit where one neutral wire
(white) is shared by the 2 circuits. If the breaker is connected to one
12/3 cable w/red, black, white + GND then that is the case. If so then
it must remain as is unless you rewire things.
If not an 'Edison' circuit then there is no reason to use the double
breaker and you could either remove the connecting bar or swap out the
double with 2 single 20's. (Verify that the wire is 12ga or larger)
There are a few ways to tell. Open the front panel and see if the leads
from each breaker go to a single cable or conduit. Then at the first
outlet see if one hot is connected there and if the neutral is bridged
where it and the other hot go to the next outlet.
Having the breakers ganged together provides additional safety. If only
one circuit is off there is a possibility that the accompanying neutral
wire is carrying current from the other circuit.
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