You are correct, the hot legs need to be opposite phases, and the breaker needs to be a double pole unit with the handles tied together.

Thanks, HU. Handles tied together, too? Why is that necessary?

For safe troubleshooting, if one hot leg trips, it is desirable that both legs be in a safe mode with both breakers tripped. A common application of such a circuit is an underwired cottage/cabin where a 12/3 line is run to a kitchen counter outlet, the common hot tab on the receptacle is broken off separating the outlets, and each receptacle is on its own breaker feed. One now has two 20A circuits available in the kitchen. If troubleshooting such a receptacle, one desires that both hot legs be unpowered when working inside the box. The common way to accomplish the breaker handles being tied together is to use a 240v breaker. This also accomplishes the requirement of the hot legs being on opposite phases.

Got it! Thanks!

I don't know what the code says, but if you run two circuits on the same phase, the current in the neutral wire would be the sum of the currents in the hot wires. If you use 10A breakers, then the 12Ga neutral could carry the current.

They do make a 12/2/2 wire that you could use if you didnt want to run two 12/2s

What is 12/2/2? 4 wires with 4 colors?

Two hots and two neutrals - instead of just one neutral.

How are they marked so that you can keep the circuits separate?

good question, mtvhike. Also, do you have a link to where this can be ordered?

You guys need to learn about Google!

It looks like Lowe's and Home Depot both carry it.

But why do you want to do this rather than just using 12-3 and a MWBC?

Glad to hear about this product. It would be good for wiring 3-way switches with the required neutral, as an example. Doesn't affect me because all my wiring is in EMT so I can pull whatever color wire I wish (within code limitations, of course).

@dennisgli: I learned about google! thank you! (grin). What is MWGC? (google says it is "Mukilteo Way Garden Club") mtvhike: I sketched it out and if power is coming into a switch box that will have a 3 way switch in it, you just have, coming out of the switch box, the 2 travelers + neutral to the next switch box (or light box) for 3 conductors total so 12/3 would be sufficient. Why would you have another steady hot (a 4th conductor) to the next switch box? Maybe so you could extend this circuit for receptacles or other lighting circuits? any other reason?

Just curious whay you would want to do this rather than installing a normal MWBC (multi-wire branch circuit)? Usually at worst you need to move a breaker over one slot to install the 240v breaker.

Consed, there are cases where you might want four conductors, a power in, two travelers, and a neutral.

@rwiegand The reason I posed the question is I'm trying to understand the wiring in our (new to us) house and had noticed these 2 circuits using 14/3 and, as HU-867564120 suggests, the 2 hots are opposite phases. I've never seen 3 wire used for this before, so that led me to the current question. I would NOT want to wire like this. I also would not want to use 14 gauge wire on a 20amp breaker. And I would not want to have 14 gauge wire going to kitchen utility circuits. This house is just full of code violations. It will take me years to fix them all (since I have a wife and a day job).

Sounds like you have a nice mess to clean up. This is a prime example of why a lot of home owners shouldnt touch anything electrical even if they think they get it.

An MWBC is a completely normal, legal. safe, and efficient way to run wiring. 14 ga with a 20 A breaker certainly isn't and will be well undersized for a kitchen. Given the amperage requirements of many kitchen appliances you're probably going to want to properly re-wire the kitchen. Depending on what else you have you can re-use those 14 ga 15A circuits for lighting, dishwasher, disposal, perhaps a range hood or 120V supply to a gas range. You're going to want at least two 20 circuies for countertop appliances, one for the fridge, and one for the microwave. The fridge is the only one of those I would definitely not put on a MWBC.

Another advantage is that if you have need for a 240 V outlet (eg for your serious espresso machine) that's easy to add when using MWBCs. It also makes it easy if you want to split a duplex outlet or four-plex outlet box into two circuits for two high amperage appliances fed from the same outlet box.

Noted. Thanks!