On Saturday, 4 January 2020 13:36:11 UTC, Dave Plowman (News) wrote:
In article ,
wrote:
On Friday, 3 January 2020 19:36:07 UTC, Dave Plowman (News) wrote:

Things with a transformer (that might catch fire) often have a thermal
fuse in the windings. Non replaceable.

often yes. And often no.

Relying on a plug fuse would be plain daft. All too easy to fit the
wrong one.

That you think it daft makes zero difference to the fact that that is
how it was done for a long time, and old appliances have not in most
cases sprouted an extra fuse since construction.

And long experience is why their aren't lots of values now used.

A fuse on say a radio etc that can be replaced has the correct type
printed beside it. No such thing on a plug.

No. It was reckoned that people could normally work out for themselves
that a radio should be on a 2A plug, and a toaster on a 15A, which have
since morphed into a 3A fuse & a 13A fuse in the square pin plug. Today
we know that often people don't know this stuff.

2 amp plug? Does that restrict the peak current to 2 amps?

No but most plugs & sockets have a current and voltage rating
and that is how you decide on which should be the maximum sustanable rating.
Those with enough inteligence know what these rating mean while it
might need explaining to others.

It's also why there are differtn types of fuses.
The most common fuses I buy are 1 amp quick blow glass bodied, which for one lab
we normally get through about 30-50 and another skills lab we get through a
similar amount each year.

The lowest current fuse I've bought is a 32ma, (a 20mm fuse) while the highest current fuse I have is a 500 amp. But strangley enough it won't fit in a
13 amp plug !
Because the fuse body is 210mm in lengh and 72mm in diameter.

I also have some 3/8th inch fuses and some 1 1/4" as well as the now standard
mains and 20mm types of which some are quick blow, semi delay, delay, and anti-surge. I try to keep a range from 50ma to 3.15 amp.