Is it acceptable to run insulated 14ga single strand through studs/ joists?
I need to extend the wiring of a 3 way switch. I have 14/2 "romex" and 14ga single strand on hand. If it is acceptable (not against code), I'd like to use the materials I have instead of buying a $100 roll of 14/3 to go 15'. I plan to make the extension connections in a j-box and run the 14/2 + single strand through ceiling joists.
I don't think it's acceptable to do it this way at all; you need to use
14/3 because code requires that the current be balanced within a single cable or pipe at all times (to avoid induction heating.) Not sure if it's a real big deal or not, but it is code.
You ought to be able to find shorter lengths of 14/3 at your local big box.
The NEC requires all conductors being used that are in the same circuit to be in the same cable or pipe (a few exceptions). In the past you could run 2 2-wire Romexes together for 4 wires. That is no longer permitted. Induction effects are a problem when all conductors don't go through the same metal pipe or the same knockout in a metal box and there is a large current imbalance.
At a local univeristy the display on some CRT computer monitors was being distorted. The problem was traced to the power transformer for the building. The secondary wires at the transformer were separated running through open air. The larger the loop formed by the wires the larger the magnetic field radiated. The magnetic field distorted the displays. Presumably this could happen in a house at 15A with the circuit wires in a large loop. In addition at the university some of the single wires ran through metal bushings. The bushings got hot enough to melt the insulation on the wire.
In the OPs case a separate wire is inadequately protected anyway.
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