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Default A guide to fuse replacement

On Sunday, 4 March 2018 19:09:25 UTC, wrote:
Coming very late into this....

Fuses are very simple beasts made complicated by a fundamental lack of understanding.


a) The nature of the load. A purely resistance load is entirely different from a motor load. Both of which are different from a filament load.

filaments are practically speaking purely resistive - as long as you're not driving them at rf, when their tiny L can become relevant.

b) How inrush current works. A purely resistance load has a massive inrush until the resistance element heats up - whereupon the load drops in proportion to the temperature.

some are like that, many aren't at all

An AA5, for instance, is essentially a dead-short at turn-on. As are most tube loads.

not so

c) The differences between motor loads, filament loads and electronic loads.
d) Rated Operating Voltage. Fuses rated below 240V are to be taken with much salt.

I wouldn't recommend salt really. 32v fuses are fine on 12v.

e) The differences between a standard fuse, a fast fuse, a slow-blow fused and a dual-element fuse. READ THE OPERATION TABLES!

and other types.

Then there's breaking capacity, a rather important thing especially with mains fuses.

And, unless you have no investment in the connected load or its fate whatsoever, eliminate all slow-blow AGC fuses from consideration - full stop (the one with the wire element wound around a ceramic rod)!!

sometimes very slow fuses are just the job. That's why they're made.