I have a question about NEC regarding a situation I discovered in my
house. I was adding a new circuit for a shop light in my garage when I
came across some 12/3 Romex that was powering some fixtures in the ADU
that is attached to it. There are two lights in the bathroom of the
ADU, one vanity light and one fan/light combo. They were running from
a run of 12/3 romex, but wired in such a way that each had its own hot
cable (one black, one red) and were sharing a common ground and
neutral. Each had a 15A breaker back in the box. My first question
is, is this allowable under NEC? Since it seems overkill to have a
whole 15A breaker for each light, I was wondering if I could just run
each hot (black and red) from the same 15A breaker? Or should I just
rip it all out and run them in series on some 12/2 Romex? I have a
little quick reference book about NEC but it doesn't mention anything
Big 8' shop lights turned out great though!
You could if the breaker is rated for two wires; otherwise you can pigtail
them; but that is ugly. Only problem might be that someone in the future
might assume it was a properly wired multiwire circuit.
Most of the breakers I've worked with are rated for two. The ones with
metal plate "washers" that clamp the wire would all be.
I should point out that "workmanship rules" (ie: comments in Knight)
say "only one wire in the panel per breaker".
Yeah, pigtailing is ugly. I hates it ;-)
If you were going by what you saw in boxes _other_ than the panel,
you'd assume the red to be part of a switch circuit (ie: three way,
or certain other arrangements such as switched outlets). As such,
I don't think there's likely to be an issue. I don't think the
NEC/CEC cares. It might be more of a "workmanship" issue, but
I don't think you'd get much resistance from an inspector on
rearranging an _existing_ circuit.
In other words, you'd be okay with reworking existing wiring, but
you shouldn't do "new" this way.
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
If the two 15A breakers are on opposite sides of the incoming 240 (an Edison
circuit), then the current wiring is OK.
What you suggest is OK from a safety standpoint, but why? The current setup
works and is code (I'm assuming). Tying the red/black together is going to
create a potentially confusing situation, since the usual assumption is "1
conductor = 1 breaker capacity", and you're violating that assumption.
You must make sure that the two breakers are on opposite legs in the
panel; in most panels this is the case if the breakers are next to each
other. This makes sure the current cancels out in the neutral instead
It does seem like overkill, doesn't it. To have the bathroom *outlet*
on its own breaker would make more sense.
(Chip C said:) "You must make sure that the two breakers are on opposite
legs in the panel; in most panels this is the case if the breakers are next
to each other. "
I have the same situation in 4 circuits of my house. In both cases the red
and black hot wires run to 1/2 size breaker paired with another in the same
slot. Can I assume when using these double 1/2 breakers, each of the
branches is on the opposite line?
In GE panels they make half sized double pole breakers that connect to "T"
slots, so it may be hard to tell. If you have a volt meter test across the
red and black of the multi wire circuit and you should read 240 volts. If
the meter reads nothing, it's wrong
If those half width breakers are really in the same slot then those two
circuits are improperly wired. As another poster has suggested you
should use a meter or voltage indicating tester to make sure that there
is 240 volts between the load (output) terminals of the breakers that
share a neutral so that the two loads balance each other and reduce
rather than increase the load on the shared neutral.
"This alternating current stuff is just a fad. It is much too dangerous
The multiwire branch circuit is legal, however your question rewarding the
bathroom wiring itself depends on when it was wired. As codes change, wiring
methods do as well. Current NEC allows two ways to wire bathrooms. One way,
all bathroom outlets can share a common 20 amp circuit. The lights in the
bathrooms can be on any other circuit. The second method is that all lights
and outlets in each bathroom be on dedicated twenty amp circuits.
Currently the ADU wall outlets are all on one circuit, this includes
the single outlet in the bathroom, so I am in violation right there I
guess. From what I understand about code when someone renovates is
that if I start messing around with it, I need to bring it all up to
code. So maybe I should run a dedicate 20A circuit to the bathroom for
the light, light/fan and outlet. Better bust out my fish tape!
Do yourself a favor and run a new twenty ampere multi wire branch
(Edison) circuit to the bath room. One leg will be the receptacle the
other will be the bathroom heater. One eighteen hundred watt hair dryer
is the entire ampacity of a fifteen ampere circuit. Even an electric
tooth brush recharger would be enough additional load to trip a fifteen
ampere circuit breaker. One you get the heater and plug of of the other
circuit the light bulbs probably won't be enough to worry about.
Well we aren't no thin blue heroes and yet we aren't no blackguards to.
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