On Mon, 22 Mar 2021 16:12:17 GMT, (Scott Lurndal)
wrote:

pyotr filipivich writes:
on Sun, 21 Mar 2021 20:22:06 -0400 typed in
rec.woodworking the following:

If you only turn off one breaker, you will often get some voltage that bleeds
back through the neutral at the supposed-to-be-dead fixture. If you used a
meter as opposed to a voltage sensor, I'll bet that it's not the full 120 VAC.

Now - although this is not something that I have ever seen - expand that to
a 4 wire source cable (3 hots and a single neutral) to the first junction box
and you've brought that 3rd breaker into the picture.

4-wire cable? It's used in dryer cables but it's a lot larger than
what you'd find in a lighting circuit.

Technically, 12-3 w/g is a 'four-wire cable' and along with 14-3 w/g
is used heavily in lighting circuits; to wit, in three and four-way
switched circuits.

Doesn't all w/g cable have a bare copper wire as the ground, now? I
know it used to be green but I haven't seen that in forever. Sure, /3
is all over the place but /4 is a different animal, at least in
residential. Obviously it makes sense with 3-phase circuits.