Two circuits in one cable

This mornings inspection had some interesting features courtesy of Home Depot Harry. A 12/3 w/ground was found in the service panel. One wire (and the grounding conductor) landed on the neutral bus, one on a 30-amp breaker (for the dryer) and one on a 15-amp breaker for the lights in another room). I know that the 12awg wire being on a 30-amp breaker is wrong and I suspect the shared circuits in the cable is wrong but can’t find the proper wording for that. Any thoughts?

How did he get 220v off of one wire. I’m sure that there are 110v dryers out there, but most require a 220v breaker, a 220v receptacle and of course at least 10 gage wire depending on distance of the circuit.

Dryer circuit improperly wired. This could be a fire hazard.
(Brown outing equipment can cause fores too!!)

Dryer circuit - Electrical wire size appears to be under sized on circuits that routinely carry heavy loads. This is a safety and fire hazard.

Non-conventional electrical wiring of multipal circuits. This may cause electrical hazards and/or fire. This may also be an electrical code violation. Your Home Inspector is not a Code Inspector an strongly suggests that the electrical system be inspected by a qualified, licensed, electrical contractor.

The third one I thinks looks the best, but may need some tweeking.

This is called a “multi-wire” circuit and is perfectly normal. Provided it is wired properly.

“Properly” would be, obviously, breaker sized according to wire size, and the two breakers being on different legs of the panel. Better yet, in a typical panel right next to each other. Many will suggest a two-pole, or handle-tied breaker.

**Edit - On re-reading, I assumed a gas 120v dryer. If this is a 120/240v electric dryer all bets are off.

You know what, I thought electric dryer when I read it was on a 30 amp breaker. But after reading your post, who knows if it is a gas dryer or electric?

It was a gas dryer. Only one side of the double breaker was used for that (improperly).

My question really was about the two different circuits being fed by different conductors in a common cable. Shouldn’t dedicated lines have been run for each circuit?

Absoultely not. A multi-wire circuit is perfectly fine, if wire right.

No. It is a common and efficient wiring method. If you think about it, it’s the same as the power coming into the house from the transformer. It is also done this way in conduit most of the time to decrease conductor count for pipe fill.

Interesting. I know multi-wire circuits for the same circuit (240-volt dryer, etc) are fine, but the differrent circuit thing threw me. Thanks Pete. Thnaks Brian.

In the case of a dryer for instance, it is not considered a multi-wire circuit.
That is simply a 120/240v circuit.

It really is kind of odd. A dryer is not considered a multi-wire, and the circuit terminates on a single device yoke.
Yet a multi-wire circuit, terminating only on a split duplex receptacle IS still a multi-wire.

Thanks again Pete.


yes, multi-wire circuits are fine if done correctly. It is also a good example of why you want the netural terminating on the neutral buss correctly when it comes to a multi-wire circuit....remove that neutral on the circuit and burn up equipment and a hazard is produced....

So people should not do multi-wire circuits unless they truly understand what is going on with them......and one important note is to ensure the multi-wire circuit has each circuit on a different leg in the panel.....lke peter said side by side on the same side ensures that.........if split up in the panel YOU run the risk of it being wrong and a neutral conductor that could be overloaded........very important to know how they work....