On Sunday, March 21, 2021 at 4:33:18 PM UTC-4, J. Clarke wrote:
Please forgive me--this is a bit of a rant.

I went to put a new fixture at the top of the stairs--the old one is
physically too small to hold anything bigger than a 60w incandescent
(by physically I mean you can't put the globe on if anything bigger is
in it, and that includes CF and LED that are larger than 60W
equivalent and in that location a 60 just isn't enough light.

Well, went to kill the power to the circuit and discovered chaos.

First:
Turned the switch off
Checked socket with a voltage sensor
Still voltage on the circuit
Par for the course in this house
Switch is in the neutral leg
Add to list of stuff to fix.

Next:
Screwed adapter into socket and plugged in tracer
Traced signal in breaker panel
Not one, but _two_ breakers showed signal
Turned both off
Went back upstairs
Checked for voltage again
No voltage--good
Flipped switch--checked again
Voltage--not good
Back to the panel
Identify third breaker, turn off
Now no voltage

Replaced fixture, turned breakers back on, everything works, I didn't
die.

But now I have the real mystery--how is this effing light managing to
be connected to not one, but _three_ separate branch circuits?


To add onto to my previous post about multi-wire branch circuit I found
a Q&A related to a section of the code that relates to Device Removal.
In that answer, the code commentary mentions 4 wire circuits, so assuming
that I am extrapolating this correctly, a 3 breaker Edison circuit might be
a thing. On the other hand, I believe that standard 3 wire multi-branch
circuits require that the 2 hots be on opposite phases. I'm not sure how that
can be done with 3 breakers.

I'd sure like to hear from an electrician or electrical inspector on this one.
It looks like Greg Fretwell (electrical inspector down in Florida) still hangs
out in alt.home.repair. It might be worth checking this out with him.

Nice guy...talked me through installing a panel interlock and 30A inlet
so I can safely plug my portable generator directly into my house.

Anyway, here's that code snippet I mentioned. I only post it because
it mentions "3- or 4-wire circuits".

....Begin Included Snippet...

US NEC 300.13(B) Device Removal.
In multiwire branch circuits, the continuity of a grounded conductor shall
not depend on device connections such as lampholders, receptacles, and
so forth, where the removal of such devices would interrupt the continuity.

The code commentary on that notes:

Grounded conductors (neutrals) of multiwire branch circuits supplying
receptacles, lampholders, or other such devices are not permitted to
depend on terminal connections for continuity between devices.

For such installations (3- or 4-wire circuits), a splice is made and a
jumper is connected to the terminal, unless the neutral is looped;
that is, a receptacle or lampholder could be replaced without
interrupting the continuity of energized downstream line-to-neutral
loads (see commentary to 300.14).

Opening the neutral could cause unbalanced voltages, and a
considerably higher voltage would be impressed on one part
of a multiwire branch circuit, especially if the downstream
line-to-neutral loads were appreciably unbalanced.

This requirement does not apply to individual 2-wire circuits
or other circuits that do not contain a grounded (neutral) conductor.

....End Included Snippet...