While working in an older unit, I was helping to track down which fuse
controlled which circuit. The fuses were in a closet, in two separate fuse
boxes. These were the screw in/screw out fuses.
There were several porcelein fuse holders and each contained 2-4 fuses. I
unscrewed one fuse and noticed that the ceiling light in the bedroom went
out. However, when I unscrewed the other fuse in the porcelein fuse holder
(there were two) the same light went out. The same thing happened for the
light in the closet.
Why would two fuses control the same light?
The porcelein fuse holders were a 4" square block for those that held two
fuses. Wires went into the back or sides of the fuse holder.
Oh, also, the wiring looks to be 12 or 14 ga (cloth covered, older wire so
it's hard to tell), and the fuses are all 30A. I'm assuming I should
mention this to the owner and mention that he should get the correct sized
Many, many years ago, it was fairly common to fuse *both*
the Hot and the Neutral lines. Not considered safe today.
You are probably not in a position to dictate to the
owner what he should do about all these problems. But at the
very least present him with some kind of statement of what was
found, for your own benefit if nothing else.
I have the dwg I made on site in front of me now. I'll see what I can do
with ASCII art - 0 indicates a screw in fuse, X and empty space in the
fuse block, and the numbers are my reference numbers:
1 0 0 5
2 0 0 6
3 0 0 7
X 0 8
Not as good as I'd like, but it will do. Pairs 1, 2, then 3, 4, and 5, 6,
then 7, 8 and finally 9, 10 are in their own, separate, fuse block. All
but 9, 10 are porcelein blocks with space for two or 3 fuses. The one with
three (3, 4 pair) only has two in it. 9, 10 has a metal box, but still
with screw in fuses. I know that 1, 2 and 5, 6 both turn off separate
ceiling lights, but each one of the pairs turns off the same light. It
does sound as if the neutral is fused. I don't have any notes on whether
the other pairs behave similarily, but could check. It's a small 1 bedroom
unit in an older building in San Francisco, CA.
Well, not always. I can recall clearly one service
which was rated at 30 Amps 120/240V.
It used 2 plug fuses for the Mains protection and a bank
of 4 plug fuses for the 4 branch circuits (no Neutral fusing).
Much more interesting though was a large branch circuit
panel in an elegant mansion built in 1900. This panel
came off a 3-wire feeder rated at 60 Amps. The interesting part
was that most of the branch circuits used an Edison 3-wire circuit
where the Neutral was shared. BUT.....they fused the shared Neutrals!!
When one of those Neutral fuses opened, the circuit voltage on any
one branch could be anything from near Zero all the way up to 240V !
Well, I've learned something new again in this thread. When I posted my
first reply I thought for sure that neutrals were NEVER intentionally
fused, because why would anyone feel a need to do that?
Was there a time when neutral wasn't intentially at at ground potential?
If someone can tell me WHY they felt the need to fuse them "back then"
my curious mind would sure like to learn more.
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