Are 3A plug fuses really necessary? Why not always 13A?

[The Natural Philosopher]

Fusing is nothing to do with power. Its about wires not catching fire.

[tabbypurr]

I didn't know this thread could get even stupider.

[John Rumm]

I assume that (non shonky) 13A leads are 13A rated, and will have a 13A fuse in the plug.

Yes I realise that other leads are available, as I am sure you know full well.

I was saying that for a lead of 13A rating, there is no point in swapping fuses about each time you use them.

Sure, but they need to 1) care, and 2) know enough to ask the question in the first place.

So you are now expecting a user to 1) recognise that the kit is 40 years old class 0 device with 10m of 0.5mm^2 CSA flex, and now work out what fuse they should put in the extension lead?

Good luck with that one.

Seen any of those Chinese three pin unfused plugs?

[John Rumm]

Because when one is engineering stuff for use by non technical people, one tries to make it fool proof and fail safe to a resonable extent.

What one designs for use by technically competent people in controlled environments is a different matter.

Bet ya do though...

[John Rumm]

Give it five mins thought and I doubt that you doubt it...

How many appliances have you seen with internal 20mm glass fuses? Were they all fast blow? All the same rating?

Thermal fuses and cutouts?

Internal fuses are typically for overload protection where there are plausible failure modes that could generate non fault over currents. (glass cartridge fuses don't usually have the breaking capacity for fault protection)

[John Rumm]

There was no original standard.

[Bill]

He is quite correct. The plug fuse is to protect the cable.

[Dave Plowman (News)]

I'm sure you might have been able to buy a non 13 amp fused extension lead once.

If you can today, I'd like to hear of where.

[damduck-egg]

G.Harman

[tabbypurr]

It's called a straw man when you invent something totally brainless, claim the other person said it then criticise it. And it ain't worth discussing.

NT

[tabbypurr]

And new compliant stuff is. So what?

Yes. And?

No, I won't be discussing a ridiculous claim that all extension leads are 13A rated.

NT

[tabbypurr]

All of which is irrelevant to picking a plug fuse for a historic item.

Hint: 20mm fuses did't even exist. And internal fuses were not usually used.

NT

[John Rumm]

Read the bit that follows:

Did you see it mention the fuse in the plug? Or did it just refer to a fuse protecting the device?

Why keep prattling about historic devices, when it has already been accepted by everyone that they are a special case? They have no relevance to current practice.

[John Rumm]

Why would you? No one claimed that.

I claimed that 13A extension leads are best protected with a 13A fuse. Not rocket science is it?

[John Rumm]

Yup, you certainly used to be able to get 5A ones. I have a 15m cassette style lead like that somewhere.

[John Rumm]

So grow up and stop doing it then.

[tabbypurr]

Current plug fusing practice they obviously do. Calling them special cases means pretty much nothing. They are what they are, and some are simply not safe on 13A fuses. End of story.

[tabbypurr]

Oh. Silly me I thought it was you that invented & argued about the idea of changing extension lead fuses every time something different was plugged in.

[PeterC]

Indeed. Also try a 5A fuse in 1kW vac - fair chance it won't last long. In the '80s a fridge plant installer wanted to know if there were slow/delay fuses for the 13A plug. As he pointed out, having a 13A fuse on a 250W device was a bit OTT. He'd tried lower ratings but, of course, the start took them out. Now, I can't remember the figures, but we put a scope on various motors, from a 4 cu.ft. freezer via a big single phase job and some 3-phase plant. The initial 1 - 2½ cycles are very high for the rating of the motor. I do recall that the little freezer would have, eventually, strained a 10A fuse.

[Dave Plowman (News)]

My first colour telly took out anything other than a 13 amp plug fuse. Despite having the usual weedy twin flex as a mains cable.