On Sunday, 29 December 2019 13:01:52 UTC, 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).

When the ring main system was introduced (in 1947, I believe), the
correct fuse was used for each appliance. Why have we moved away from
this commonsense arrangement and apparently degraded a safety feature?


A few things have either changed or been more widely recognised since the 1940s.

Back then appliances were routinely not suitably fused & designed to safely deal with internal faults. The plug fuse was a safety device for the appliance as well as the lead. Now it's usually not, it only remains so for historic appliances.

Leads were often very thin, basically what we now call speaker wire. Using under 3A fuses is wise if such wire is used.

Now most people are not expected to have any clue what value of fuse an appliance can or should run on - and don't. In the 40s it was expected that people would have some idea on this.

The financial saving of having fewer choices is now widely recognised & appreciated. Stocking 3 & 13A is cheaper than stocking 1, 2, 3, 5, 7, 10, 13A.

Ultimately yes, it's always safer to use the fuse that best suits each appliance. For historic goods that matters far more. I don't have any real data on what difference that approach can make to fire & death stats.


NT