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.


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.

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.

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.

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.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.