Thread: Fuses
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Old 22nd Mar 2014, 12:42 pm   #43
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 5,488
Default Re: Fuses

General rules I adopt:

Use current rating 25-50% above the maximum steady-state current the equipment can draw.

Ensure voltage rating is at least equal to the circuit voltage.

Use anti-surge (T) types if there is a switch-on surge, otherwise normal (F).

If the supply impedance is low (ie operates from mains) use ceramic, sand-filled high-breaking-capacity (HBC) fuse. Otherwise, glass types so you can see if they've failed.

Use 1.25" fuse rather than 20mm whenever possible.

If in doubt, arm yourself with a dozen spare fuses and replicate/simulate the possible faults. Ensure the fuse does its job each time. (Makes a mess of the equipment, but great fun).

I do confess to using a 250V-rated fuse (1.25" type) on a 400V 10A DC rail, but it was to hopefully save the PCB in case of a downstream fault, not as a primary means of safety protection. As it happened, it was never put to the test.
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