On Monday, 17 August 2020 22:29:49 UTC+1, Cursitor Doom wrote:
On Mon, 17 Aug 2020 21:57:17 +0100, John Rumm
wrote:
On 17/08/2020 16:59, Scott wrote:
On Mon, 17 Aug 2020 16:20:35 +0100, John Rumm
wrote:
On 17/08/2020 14:04, Cursitor Doom wrote:

Seems there's even more leaway than I'd expected for extended
over-current tolerance. Perhaps we should never fit anything bigger
than a 10A fuse in a 13A plug? I think I'll toss out all my 13A fuses
to be on the safe side.

You could flip the argument, and say never fit anything other than a 13A
fuse. The purpose of the fuse (for any moderately recent appliance
anyway) is to provide *fault* protection to the flex - and a 13A fuse
will do that just fine.

The exceptions to this are some low quality multiway extension leads
where 10A would be more appropriate, or for historic appliances and
flexs, or cases where a manufacturer explicitly cites a smaller fuse.

I have seen this argument so many times before and have never
understood it at all.

ok.

I acquired a supply of 2 amp fuses and fitted
them to various low current appliances, without any difficulties. How
anyone can argue that limiting the fault current is anything other
than a safety enhancement confounds me.

Because you are confusing fault current with overload current. Fuses (or
any other circuit protection device have *no* ability to limit fault
currents. The only thing that limits a fault current the round trip
impedance of the circuit with the fault. So if that is 0.23 ohms, then
your fault current is 1,000 A regardless of the fuse fitted.

That will open any BS 1362 fuse pretty sharpish - the nominal current
rating is not important.

What matters is that the fuse has the breaking capacity to clear the
fault before something else (like the appliance flex) is destroyed /
catches fire.

This is a *totally different* discussion from overload protection - foe
example fitting a 13A fuse to a spur feeding multiple sockets on a ring
circuit.

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10 and
13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They will all
handle fault currents.


You frequently use the term "fault current" which crops up frequently
when professional electrical engineers are discussing installations.
However, for everyone else, it requires clarification. I'm not an
electrician, so I have no idea when you use that term whether you're
referring to *short circuit* current or *earth leakage* current or
something else altogether (unless you use an example as you did above
but even that's not watertight). And then there's that lot that read
this through Homeownershub - God only knows what *they* make of it.
;-

The electrical wiring regs' meaning of 'fault' is a hard zero ohm L-N short.. John uses that meaning. Those of us that are more into repairing things tend to use 'fault' to mean any failure to operate correctly. The I with some Es seems to like to define existing terms differently to everyone else, classic communication poor practice.


NT