If I may add a few things....
PT> The house is circa 1960. The electrical panel is glass fuses. The whole
PT> house runs off the box of 8 glass fuses. They are 30 amp.
PT> I wonder if the electrical fuses should be 20's and someone has replaced
PT> them with 30's. How do I determine what is the correct size?
As someone else mentioned, probably the best thing to do would be to
have an electrician look at what wiring size is (the guage) and insert
the correct the fuses accordingly. FWIW there are "circuit breaker
fuses"; maybe was -- I looked into these several years ago for our
panel (1 15 and three 20's for the original house). They can be used
in place of 'normal' sized fuses. Couldn't use them here because at
one time adapters were inserted so only the correct sized fuse could
Another reason to obtain the services of an electrician is to
determine if damage has occurred to the wiring due to these overloads.
The electrician can also look for loosened wiring -- this can occur
due to aging of the system.
(I would strongly suggest getting a new service panel installed. It
was something I wanted to have done for several years but we finally
had to have done with the addition. Went from four glass fuses
(original house) and two circuit breakers (for the Dining Room
addition by a previous owner) to something like 20 circuit breakers.)
PT> The tenant blew a fuse, running a leaf blower and fryer all at the same
PT> time. I told her to try a 20 amp fuse first, but she said it sparked and
PT> wouldn't physically screw in. (did she have it crossthreaded, I don't know
This sounds a little suspicious to me. I don't want to sound like I'm
calling the tenant a liar but with the system here the fuse had to be
screwed in pretty much all the way to make contact. The contacts are
like that of a light bulb: at the sides and at the bottom.
PT> But the 30 was fine. After a couple of hours after replacing the fuse, I
PT> asked her to feel the panel box and notice if anything was warm or hot...shPT> said no.
I wonder if she felt the outside of the fuse panel rather than the
tops of the fuses?
PT> Are the 20's and 30's the same size?
The standard ones might be -- the sockets the adapters here screwed in
to looked to be all the same size. The adapters had two different-
sized openings. (In case anyone is wondering, the adapters were held
in place with a two spring wires angled so could not be unthreaded.)
PT> If the box was built for 30's and I replace them with 20's, what's the
PT> damage? And vice versa.
The smaller the number the less current can flow before the fuse blows
(actually the excess current starts to melt the fusible link inside
the fuse; the link will spark when it blows). A 100 Watt light bulb
uses approximately 1 Amp. So, 20 100W light bulbs will use
approximately 20 Amps; 21 100W bulbs will use 21 Amps and should blow
a 20 A fuse (or circuit breaker); there is a little bit of a fudge-
factor so the fuse or circuit breaker will probably hold for a while.
However, one is overloading the wiring between the fuse and these
light bulbs -- not a good thing.
If someone some time back replaced the 20 A fuse because the "darn
thing kept blowing" with a 30 Amp fuse then the _fuse_
not not blow
until the load reached 30 Amps but the _wiring_
is only rated for 20
Amps (and the outlets and light sockets are probably only rated for
15!). I'm not going to say the wiring was glowing like a red-hot
toaster element but it was starting to get a little warm!
PT> How tough is it to replace a glass fuse breaker box with a modern breaker
Relatively easy for an electrician. LIS we had ours updated with the
addition -- think it was $1400 but that also included moving the
electric meter to the outside (it was in the basement next to the old
panels). The contractor coordinated with the electric company to cut
and restore service -- actually I think the electricans cut the meter
seal and removed the meter. Power company installed the new meter
when the new panel was installed. I think we were without power at
the house for two, maybe three hours at the most, and then sections of
the house were brought on-line (as wiring was connected to the circuit
breakers). ...The whole thing was carefully (?!) orchestrated as the
contracted had to have power for his men to continue building ==> the
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