why do we do this, what are the benefits, and does it make troubleshooting down the road more difficult?
In my new job, one of the jm doesn't explain too many things...
there were 2 3-ways in a 2gang. old wiring with the paper... the neutrals were hots, and there was a red from one and a white from the other merretted together loose in the box. Where was the switch leg??
It's a white as hot - not a neutral as hot, please. We do it because we don't want to use two kinds of two wire cable and two kinds of three wire cable, one with a white and one without. As it is, I can barely move around in my truck with one kind of each in non-metallic and bx both in several sizes.
There is a specific way to connect the wires, which makes troubleshooting easier.
Perhaps someone can provide a link to a 3 way switch diagram?
You are required to use the white in a cable as the hot on a switch leg if you are using it as an ungrounded conductor and since 2002 or so you are required to reidentify it with tape or other method. 200.7(C)(2) The thinking is the return from the switch will be a "phase" color when it gets to the luminaire. Then the installer will be presented with a white neutral and a phase color for the ungrounded conductor. It can get a little confusing when you are on the supply end tho. That is why they started requiring reidentifying the wire.
That's an interesting practice... in Europe mostly the black/brown wire in the switch leg is used as the permanent hot and the blue as the leg to the fixture. Usually there's a junction box in the middle though where the "hot blue" changes back to black or brown.
Where conduit is used it's good practice to use a different phase color like brown (if the other phases are black), orange or purple for the switched hot. So either the power source is at the switch or at a junction box, due to the lack of ceiling boxes except for cast concrete ceilings we can't really make any connections beyond the fixture splices at the fixture.
It's a good thing to remember - never trust a wire color. Oer at the violation photo board you can see pictures of green hots and everything... always expect to encounter hack work rather than risk your life by trusting someone you don't even know (the guy who installed the old wiring you're working on).
Another time you'd use white as a hot is a 240V circuit. Unless, of course, you want to run 12/3 (unneeded expense)and have an unused white at the load. You would/should have to land the white at the panel though, if you did that. I have seen 6/2 WG that has black and red wires (there is some in my house), but I have never seen it for sale myself. So, I don't know if it is even available anymore.