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pete0403 08-14-2012 03:34 AM

Separating a Milti-Wire Branch Circuit
I'm finally getting around to doing this...

See this thread for background:

I have a box near my panel where the wires didn't reach when the new panel was moved to the other wall. These two wires are run to this box and then run about 4 feet to the panel with 14/3 to two full-sized breakers with a breaker tie between them.

I'm going to separate these circuits because one circuit is my outside receptacle/lawn light and the other is my furnace. I'm planning some electrical work outside and I don't want to have to turn off both circuits or disconnect the outside circuit each time. I know I could put in a switch but I've never felt comfortable relying on a switch just being off between me and 110V.

What I want to do is replace the one junction box with two and run 2 14/2 cables to the panel.

My question is: Do I need to buy two new breakers or can I just remove the breaker tie from the two that are there now. this is a Siemens panel and the breakers are full size (ie: not the little double breakers)


rjniles 08-14-2012 05:28 AM

For 2 $5 breakers I would not modify a UL listed device.

pete0403 08-14-2012 05:42 AM

I wasn't sure if breaker ties were added after installation or not but if they're manufactured that way, I won't change them.

I'll just replace them then...I didn't know breakers were that cheap.

Thanks a lot

AllanJ 08-14-2012 05:51 AM

You can leave the double breaker in place and connect two separate circuits to the halves of the breaker, superceding the multiwire branch circuit.

You can re-arrange the branch circuits in the panel so a different pair of circuits uses the double breaker and your outdoor circuit goes to an existing single breaker.

As far as the outside receptacles go, an ordinary switch in the branch circuit just as it leaves the panel is the same thing as the breaker itself as far as killing the circuit is concerned. People are advised to flip the breaker off as opposed to just turning off a switch up in a room because at first glance it is not certain what is killed and what is still live when the switch up in a room is turned off.

Breaker trips do not happen often in the average home. Here, the double breaker will flip off both circuits if one trips but this is really not an inconvenience since you will be flipping the breaker back on in a few minutes.

(changed) Also there is no real urge to replace the 14-3 or 12-3 of a MWBC coming out of the panel. Just leave it as is, except you can separate it into two separate circuits in a junction box a few feet or several feet away. .

After the two separate (14-2 or 12-2) subcircuits split off, each of them follows single circuit rules downstream, not MWBC rules.

Single circuit rules also forbid taking hot from one branch circuit or subcircuit for a given load and using neutral from another circuit or subcircuit. There must be exactly one neutral path for each load and that path must be conductors accompanying the hot feed.

pete0403 08-15-2012 12:05 AM

Thanks AllanJ. You're idea at the beginning of your post is a good one except the only other curcuit at that side of the panel is the air conditioner (240V 30A). Everything else is on the other side of the panel and won't reach and the breakers there are all tandem so it wouldn't work to move the breakers around either.

I bought two new tandem breakers (Sice I'm going to be adding a patio light soon) and am just going to split the MWBC apart as 2 separate circuits. I also bought two new boxes since I assume I have to replace the original box with a new one for the furnace circuit since it will now have an empty pop-out.

Thanks for the help :thumbsup:

I got all excited at the hardware store when I saw that I could buy a GFI breaker for the outside curcuit until I saw the price ($85:eek:) so I'll be sticking with a GFI receptacle to protect itself and the lamp post run from it.

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