@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.
