AC Power Question

Being an Electronics Engineer, I live in both sides of this equation. Take this example:

Builders do the dumbest things you can imagine, which further compounds issues. For example, my 3000 sq ft house has a second floor laundry near the front of the house, and the breaker panel is in the basement on the opposite side near the back. In their infinite wisdom, they ran 14/3 Romex for the circuit that powers the clothes washing machine, which is some 130 feet long. The punch line is this: they used the other leg on that 14/3 for lighting in the first floor. Every time the clothes washer was running and switched cycles, the lights would flare. No wonder they would burn out so often, with all that excess back-current! I fixed the problem by running a new 14/2 circuit just for the lighting, and one day, when I feel more motivated, I’ll run a new 12/2 for the 15 amp circuit feeding that clothes washer. 

The load placed on each of Lowrider57’s circuits is minimal and relatively steady. Placing both on the same leg is good practice based on the application. If you think you’re going to have a perfectly balanced panel just by arbitrarily splitting loads, you are in fantasy land. The only way to balance a panel is by doing measurements, and even then at one instant the balance will be different than the next. 

@cleeds 

Will you please explain what "back-current" is? If you have a 14-3 cable, then each of the hot wires come from different legs of your service, correct? (After all, that's why they can share a neutral.) Please explain how a changing load on one leg can influence the voltage on the other leg.

If your 14-3 cable is connected to the same phase (leg) of your AC service, that's a code violation because of the shared neutral, no?

On a shared neutral such as 14/3, the back current is reverse flow from the red leg affecting the neutral potential for the black leg and vice-versa. That’s why shared neutral circuits sometimes use a smaller gauge neutral conductor. When both sides are steady loads, such as lighting, you can do shared neutral, but in the case of the circuit powering my clothes washer, the other leg powered a lighting circuit, which caused the lights to flare when the washing machine was changing cycles and electrical demand from it surged. 

Shared neutral circuits must never have both hot conductors on the same leg of breaker panel. That would cause the neutral load to reach double the current rating, and create fire hazard. Shared neutral should be against code in my opinion. The correct use for 14/3, 12/3, 10/3 etc... is 240 volt loads that require a neutral conductor, or sub panels. 

My situation is a 15yr old house governed by Canadian electrical code, which is for the most part consistent with the US NEC. The reason the builder used 14/3 for those branch circuits was purely economics based. In Canadian electrical code, a clothes washer circuit is only required to be 15 amp. Should it be on its own? - yes! Should it be 12/2 instead? - yes! But, the reality is this house was built in a large development project, and they didn’t do things to meet ideals, they based every decision on the bottom line. One fine day, I will get around to running a dedicated 12/2 for that clothes washer. As an intermediate stage, I removed the lighting circuit from the other leg of that 14/3 and put it on a dedicated 14/2, which has improved the lifespan of lightbulbs.