Two fixtures from 12/3 romex? NEC question

Hi all,
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 about this.
Big 8' shop lights turned out great though!
Thanks!
-JDS
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Look for "Multi-wire branch circuit". Yes, they're legal. I prefer that the breakers be tie-barred, but in this case they don't need to be under NEC. (Under CEC they do).

You could.
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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.

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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.
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What is ADU?
If the fan light has a heat lamp in it, a separate circuit might be a good idea.
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Attached Dwelling Unit.

Not a bad idea..
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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.
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JDS wrote:

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 of adding.
It does seem like overkill, doesn't it. To have the bathroom *outlet* on its own breaker would make more sense.
Chip C Toronto
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(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?

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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

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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.
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I will check but the point is moot anyway since I plan to upgrade to a 200A panel and change everything to fullsize breakers. My Zinsco panel is not the best to begin with, Cant even get AFCI breakers

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Hey all, sorry about the direct replies. I meant to reply to the group.
Thanks for all the help.
-JDS
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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.

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RBM (remove this) wrote:

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!
-JDS
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JDS wrote:

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.
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HorneTD wrote:

Great idea! I can just rewire the existing wire and leave it in place. Put the lights and fan on the on leg and the plug on the other.
-JDS
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