Fuses

Nope. And AFAIC in this type of fuse of that rating, there normally isn't any in any case.

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. ;->

We used to use strips of milk bottle tops back in the day. But I'm giving my age away now. ;-)

The BS refers to "granular filling"

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 t end to use 'fault' to mean any failure to operate correctly. The I with som e Es seems to like to define existing terms differently to everyone else, c lassic communication poor practice.

NT

Probably fake - the end caps look too shiny to be Bussman

Agreed - hence why I mentioned it.

However a good deal of appliances (even then) don't actually need any overload protection... So there is a danger that you could cause more problems in the quest for "safety". (i.e. nuisance fuse blows, plugs running warmer etc).

I don't have a source of figures for how many are still out there. Do you? Some, sure; millions perhaps?

Define safer?

So if your life support system were to fail with a blown fuse when there is a mains spike because some well meaning but uninformed person replaced the manufacture fitted 13A fuse with a 2A one "because its safer", that would be better?

Think it though logically, what are you trying to achieve? Say you have a table lamp that takes a single B22 fitting lamp. What is the highest power lamp that it will take in that format? 250W or about an amp? Is there any way a lamp could draw say 2kW for a sustained period to put its flex at risk of dangerous overheating? The answer is not really (at least not without determined and conscious action by the user to be a complete numpty).

Now you say, ah but, its a lamp, 3A fuse is better... in a sense you are right, there is no downsize other than needing to replace the one fitted by the manufacturer. But what have you actually achieved? The thing that does matter (i.e. power gets swiftly disconnected when you stick your chair leg down on the flex and cause a short circuit), will happen regardless of fuse rating, since you have say 100A of fault current to play with[1].

Now there are some appliances that do have overload failure modes. If they are old enough, they may not include their own protection, for those, yes its important they are fitted with the "right" fuse. For others it matters less than many worry about.

s = sqrt( 100 ^ 2 x 0.1 ) / 115 = 0.27mm minimum CSA

(115 being the k factor for PVC insulated cable)

So even the smallest typical 0.5mm^2 CSA flex would be fine with any fuse.

Indeed I do - and perhaps I assume (maybe too readily) that since its discussed so often here, most readers will be aware of the term and how understanding it is fundamental to the concepts of circuit protection.

Here is a fairly succinct explanation:

(using the terms in the context of circuit rather than appliance protection, but the same principles apply generally even if overloads within a single appliance are harder to create)

A faucet probably:-)

It does, although its a kind of implied requirement. In section 8.1 on general requirements for testing, it says

"If acceptance tests are required, they shall be selected from the type tests as agreed between the manufacturer and the purchaser. Fuse links supplied by the manufacturer shall be regarded as complying with the requirements of this standard, provided that in the following respects they are identical with those tested in the type tests:

I find people are surprised we still have milk bottles (as deposited on the doorstep at 5am by Kevin our milkman!)

or L-E

Being one who also repairs stuff, I am fully aware that the colloquial use of "fault" is far less specific than that when used in engineering and standards documentation for electrical systems. However if you are going to have a meaningful discussion on fusing etc, it is quite important that everyone uses a consistent set of terms when it matters.

So sure, I am quite happy to agree that my radio may have a fault because it can no longer receive FM, or the computer PSU has a fault due to too much ripple on the 5V rail - but you do need a way of describing and differentiating between when something has gone badly wrong and a device is now trying to ingest the full output of the local substation, Vs. its taking an amp and should only be drawing 50mA.

And it failed miserably. If a fuse blows, all the vast majority will do is replace it to get it working again. And are very unlikely to have all those values to hand. And the spares they are likely to find, 13 amp.

Hence the current method of having wiring capable of taking out a 13 amp fuse if there is a sort somewhere without causing a fire. And protecting the device itself with its own fuse if needed.

those aren't dangers. And putting a 3A fuse on a 2A load does not cause nuisance trips.

I don't have a record of where they figures came from. But it's easy to come up with a very rough idea of the size of the issue.

1. How many substandard appliances have major retail sites sold?
2. How many PAT fail appliances are there per site? What proportion need & lack overload protection.
3. How many historic appliances are still in use? If you find just one per 63 people that's a million.

NT

define waste of time

With respect 99.999% of appliances are not life support. That different safety issues apply to that miniscule percentage is not news.

more safety

You're barking at nonexistent shadows there. Any appliance can get a smouldering insulator fault that takes >>3A but not >>13A. That's one way appliances catch fire.

any insulator can fail smouldering. All appliances include insulation.

many modern ones don't either as your tablelamp example shows

ah, we agree after all

Yup. But the chinese flea bay special with copper coated steel mains lead would catch fire. Proper flex that's partway broken also would not cope, and that is not a rare failure mode.

NT

No, the usage of 'fault' to mean zero ohm short only is specific to UK wiring regs not specific to engineering.

Good luck with that

On the contrary it was much more effective than the prior system

which is fine

IME most people had 3A & 13A.

Yup. But historically it did work a lot better than the old 2/5/15A system.

NT

IMO changing to a 2 amp fuse can only nudge safety in one direction.

Having blown 13 amp BS1362 fuses in the past, whatever I was doing that caused the fuse to blow, drowned out any noise the latter might have made.

An elderly person getting ripped off after a blown fuse is 'diagnosed' as a non-repairable item.

Most (many) domestic fires these days are caused by fake chargers and /or rechargeable devices, including genuine ones that were not fakes.

Wibbling about fuses doesn't seem to be relevant to these.

You can include Soviet colour TV's in that group, but not our problem, though Hotpoint/Beko white goods are, even though they are fitted with the 'correct' fuse.