On Sun, 09 Apr 2006 23:49:57 GMT, (Doug Miller)
wrote:

In article , mm wrote:

But you remind me of a long time question I've had.

When I lived in a 1930 apartment building, the fuse box in my apt. had
2 slo-blo 15 amp fuses, and in the basement the fuse that served my
apt. was 1 slo-blo 20 amp fuse.

I was told this was bad, because 2 x 15 = 30 which was more than 20.
I was told the sum of the fuses downstream should never be more than
the upstream fuse. Any truth to this????**

Nope. The current is limited to 20A max, no matter what the downstream fuses
are. Fuses are sized to the wiring they protect. Period.

OK. I'm happy. It's been a long time but I thought one or two people
said it was bad at the time, and that 2 or 3 others have said it was
bad since then. Whoever did complain to me, it seemed like an
absolutist rule that didn't make sense. I'm glad it's not a rule
after all.

Thanks. Several more reply lines below, but this was the essence of
it.


I sort of figured first, that the landlord would not rewire the whole
building and I needed my 30 amps, so I should keep my mouth shut.

You weren't getting 30A, only 20.

Right. My mistake. I really needed my 20 amps. 4 people for a few
years, and later 2 people and one room air conditioner. I also worked
things out so I could go to the basement to change the fuse in the
middle of the night without bothering the super. I think I replaced a
blown fuse about 10 times in 10 years. Somewhere between 8 and 18. I
vaguely remember a short period where I blew a whole bunch, but I
can't remember why. 18 in ten years doesn't seem like too many.

Compared to I guess 200 amps I have now, I really was not constrained
much by having only 20. Washing machine, no dryer or course, gas
stove. Plenty of lights, radios, I might have had two tv's on at once
once in a while (one in the kitchen), but iirc no roommate (I had
about 20) ever had even one tv. I wonder why not.

second, the building had been working this way since
1930 and there were no electrical fires, and that's still true today,
75 years after construction.

No surprise -- nothing inherently unsafe in what you've described. Silly,
perhaps, but not unsafe.

I think this is typical for 100's or thousands of buldings in NY.
Immigration was high all the time, but especially the 1880's to 1914,
I think it was, so there were plenty of buildings nicer than tenements
being built by the '30's. The war may have prevented much building in
until '45, and after that there was probably more electricity provided
for each apartment.

In the garbage room on our floor (where there was a chute that led to
the basement, where the garbage was first burned and then later
compacted, there was a sticker on the wall: "Save your cans. Defeat
the Axis." They only painted this tiny room every 20 years or so --
it didn't seem to get dirty -- and when they painted in 1980, they
didn't paint over this.

and third, the 20 amp fuse in the basement would protect
the 12 gauge wire from the basement to the 5th floor. That was its
job. But there were sometimes I would use 14 amps through one fuse
and 5 through the other, and that would be under 15, and under 20
total so what's wrong with that.

Nothing.

Anything higher would blow one fuse
or the other.

**If there is any truth to the idea that two 15 amp fuses can't feed a
20 amp fuse,

Ahh, now that's a different story. Two 15s feeding one 20 is not the same as
one 20 feeding two 15s.

I meant to say it the other way. Or I was looking at "feeding" in a
different way. But regardless, I didn't mean anything different from
before.

why is it all right for the sum of all my circuit
breakers to be greater than the main serving my house.

It's just not a problem.

I have cb's
totally 200 or more amps now, and room in the box for in the box for
120 amps more. Maybe more. I'll never use anywhere near all of it
at once, but if this is ok,

It is ok, and that's why -- you won't ever use anywhere near all of it at
once. For example, the probability is near zero that you'll ever use your air
conditioner and furnace simultaneously. It's also quite unlikely that all of
the lights in your house will be on at once, or that you'll simultaneously be
using all of your appliances.

why was my apartment setup not ok??

It was ok, at least as you describe.


BTW, slo-blo is only 5 or 10 seconds, right? It's more than 1/2
second like non-slo-blo, but no where near 30 seconds, is all of this
so?

I never timed one, but yeah, it takes a little while, but only a little.

That's what I thought.