I live in a 1977 vintage apartment building in the US. I have two 3-pole switches for my bedroom entry light, which are not working correctly. The one switch must be left in the "up" position all the time in order for the other switch to be able to turn the light on or off. They do not work independently of each other like they should. Upon opening up both double gang switches, I noticed that one of the white neutral wires on each switch is separated from the others. Could that be the missing traveler wire? Also, does a three pole connection require use of a 14-3 cable, which has a red wire which I hear is the only color for a traveler wire. One double gang box has four 14-2 cables. The other has three 14-2 cables and one 14-3 cable, but that is already being used for a switch controlled outlet.
The answer is yes in 1977 the white was regularly used as a switched leg. There are 2 travelers. It sounds like someone has replaced the switch in the past and mixed up a common for a traveler ( in This case common is the switch contact that toggles from 1 traveler terminal to the other) This is quite common in DIY where someone did not pay attention to the original wiring.
The governing rules here:
- green, green/yellow or bare must be ground.
- white or gray must be neutral.
- any other color is a hot wire.
- a white or gray wire can be re-marked to be a hot wire with tape, shrinkwrap or paint. Historically the marking could be omitted if the usage was "obvious". In practice this meant the electrician was in a hurry. Generally you re-mark with a color legal for a hot.
In a 3-way (UK 2-way) switch loop, all the wires are hot. So yes, you would re-mark a white wire as another color.
Give n free choice of wire color, it's fine to make both messengers the same color. They should be distinct from everything else, though.
Today, there is an NEC requirement to bring a real neutral wire to most switch locations most of the time. In that case, a switch loop would use 14-4 cable, or 14-2-2, which is now becoming more readily available for that reason.
14 ga wire is okay for lights only. 12 ga is for general use around the house. 10 or even larger is for special heavy loads. There are, of course, calculations around this stuff, that you should look up in such cases. The main point, however, is that 14/3 is okay for the scenario posted. (There exists 12/3, of course, which also would be okay, but not necessary.)