I have a 100 amp service with fuses. Have read a couple of the threads about fuses.
Is it a hard and fast rule that a 100 amp service should use only 15 amp fuses, or can there be a few 20 amp fuses if the wires support 20 amps?
Is it a hard and fast rule that a 100 amp service should use only 15 amp fuses
Not only is it not hard and fast, it isn't even a rule at all. Where did you hear that? You probably have a bunch of circuits that aren't 15 amps. For example, water heater, dryer, etc.
If the wiring can support it, there's nothing wrong with using 20 amp fuses. You just can't switch out 15 amp fuses with 20 amp fuses without being sure that ALL of the wiring on that circuit is able to handle 20 amps.
A 100 amp service is old, when not many electrical loads had even been considered, though I had a house once that had a meter with 30 amp contact ratings.
It still had 240 V though.
You can still load it up with any size branch circuits you need (up to the 100 A limit of course).
A huge arc welder, electric tankless water heater, or other special loads might be a problem.
An actual load calculation will tell you when you are getting close.
Keep in mind the sum of the branch circuit ratings in your case the sum of the separate fuses) does NOT indicate the actual load present.
Many a 200 amp panel has well over 200 amps of branch circuits installed.
'Load diversity' means that not all the branch circuits are pulling there rated capacity at the same time.
This post was edited by brickeyee on Thu, Apr 4, 13 at 13:36
The big downside to most 100A load centers is the limited number of slots. There are no 42 breaker 100A load centers.