On Sun, 29 Dec 2019 13:01:47 +0000, Scott
wrote:

Fuses are available as 1A, 2A, 3A, 5A, 7A, 10A and 13A yet only 3A and
10A seem to be in common use.

I've been checking some fuses (when I got bored over Christmas!) and
many seem to be far higher than needed, most notably a printer fitted
with a 10A fuse when the rated current is 2.5A. I changed this to 5A
(to leave some headroom). The toaster does not need 13A; 7A is fine.
LED lamps do not require 3A. 1A seems fine.

I appreciate that the fuse is intended to protect the lead not the
appliance, but surely there is a side-effect of protecting the
appliance? Is there any benefit in fitting a fuse significantly
larger than needed? Common sense suggests go for maximum protection.

I appreciate that motors have a surge at the start. I believe a 50%
margin should be added generally (more for a motor).

BS 1362 plug fuses already have a margin greater than 50% built in. A
13 amp fuse can take 20 amps for a long time before it fails.

See:

https://www.diynot.com/diy/threads/b...istics.430472/