Ten Amp Fuse in a Telly Plug (aka plugtop)

[JohnW2]

Are there no examples for this theoretical possibility?

As I wrote this afternoon, when BAS asked essentially the same question (in his inimatable style - "Will you please cite the evidence ...."), it'simpossible to provide any evidence. If an item of equipment develops a fault which causes a low-rating fuse to blow, one can't know whether it would have suffered more damage in the absence of the fuse. If an item of equipment which is not protected by a 'low rating' fuse suffers damage due to a high-current malfunction, one can't know whether it would have suffered less damage if it had been protected by a lower-rating fuse.

It's just like RCDs 'saving lives'. If, in the absence of an RCD, a person suffers a fatal electric shock, one cannot know (unless one is somehow certain that it was a purely L-N shock) what would have happened in the presence of an RCD. If a person survives an electric shock which caused an RCD to operate , one cannot know whether they would have survived in the absence of the RCD.

As you say, it will do no harm but the question is "Does it do any good?"

All I can say is that it is not impossible that it could do good. Given that I have large vats of 1A and 3A fuses, the cost and effort of doing it is minimal, so why not? Millions of people (albeit not me!) buy Lottery tickets!

Kind Regards, John

 

[EFLImpudence]

I think that it boils down to the fact that -

if an appliance needs a small fuse then the manufacturer will have fitted one - not doing so would be irresponsible - and so fuses protecting the cable/flex can be sized for the cable/flex and no benefit will be gained as far as the appliance is concerned.

The OP's TV will have a couple, boilers have a couple, etc. I have even come across some standard lamps which have one protecting the inevitable (these days) circuit board.

Of course, many appliances cannot cause an overload so we could scare the OP and doubters by saying that for these items it may be that actually no fuse at all is needed.
We just have to put something in the plug/FCU so, as you say, it may as well be the smallest - by that I mean 3A; there's no need to calculate the milliamps - but it doesn't matter.


I have, in the past (only once), blown a DNO 60A fuse with a 1mm² CPC resulting in the smallest of globules where it touched.

 

[JohnW2]

if an appliance needs a small fuse then the manufacturer will have fitted one - not doing so would be irresponsible ....

Well, manufacturers have been known to be irresponsible! However, it's not really as black and white as you suggest, since there is no clear definition of "needs". Very many items which contain electronics (i.e. most current-using equipment these days!) will contain conductors which could not tolerate 13A, but might survive 3A or 1A - but many of them, particularly the smallest, lower power and (probably) most vulnerable aren't deemed to 'need' fusing.

The OP's TV will have a couple, boilers have a couple, etc. I have even come across some standard lamps which have one protecting the inevitable (these days) circuit board.

Yes, but you are talking fairly 'big' bits of equipment. It's the small boxes of electronics, even just PSUs, which take a dozen or three watts that often won't have internal fuses.

Of course, many appliances cannot cause an overload so we could scare the OP and doubters by saying that for these items it may be that actually no fuse at all is needed.

Agreed - but, of course, if one is using a BS1363 plug, one has no (acceptable!) option other than to have a fuse.

We just have to put something in the plug/FCU so, as you say, it may as well be the smallest - by that I mean 3A; there's no need to calculate the milliamps - but it doesn't matter.

Indeed - so are we agreed?

I wouldn't do any formal calculations, but if I knew the equipment in question only used 'a few dozen watts', I would know that 3A was unnecessarily high, so would probably use a 1A fuse.

Kind Regards, John

 

[EFLImpudence]

.

Well, manufacturers have been known to be irresponsible! However, it's not really as black and white as you suggest, since there is no clear definition of "needs". Very many items which contain electronics (i.e. most current-using equipment these days!) will contain conductors which could not tolerate 13A, but might survive 3A or 1A - but many of them, particularly the smallest, lower power and (probably) most vulnerable aren't deemed to 'need' fusing.

Then how will they manage to draw whatever current they cannot tolerate?

Yes, but you are talking fairly 'big' bits of equipment.

The OP has a TV set.

It's the small boxes of electronics, even just PSUs, which take a dozen or three watts that often won't have internal fuses.

Then a track will melt.

Agreed - but, of course, if one is using a BS1363 plug, one has no (acceptable!) option other than to have a fuse.
Indeed - so are we agreed?

We are agreed that something has to be inserted in the plug.

I wouldn't do any formal calculations, but if I knew the equipment in question only used 'a few dozen watts', I would know that 3A was unnecessarily high, so would probably use a 1A fuse.

You can go on saying that to convince yourself that it is doing some good.

Is Europe burning?




I liked your first reply - in both senses - and was surprised but then you reverted to prevaricating mode or is it playing Devil's advocate as you say you sometimes.

It doesn't really matter. There will (hopefully) be a fuse (or fuses) inside the telly (probably a lot less than 10A) to protect the telly as much as any fuse could, so the fuse in the plug is only protecting the bit of cable between the plug and the TV.

[ and, just for the record, it would take a lot more than "2000W" (about 9A) to blow a 10A fuse - probably double that ]

 

[JohnW2]

We are agreed that something has to be inserted in the plug.

Indeed we are, but you went further than that and said of that 'something' ... "as you say, it may as well be the smallest", so you presumably agree with that as well?

You can go on saying that to convince yourself that it is doing some good.

As I keep saying, it's not a question of "doing some good", since the chances of it ever 'doing good' are extremely small, but that is is conceivable that it might one day 'do good'. If plugs came without a fuse fitted, I would say that it would be a no-brainer - if I had to reach into my store cupboard, grab a fuse and put it into the plug, why on earth would I choose a 10A or 13A one when a 3A (or maybe even 1A) one would be adequate (and 'might just conceivably' one day 'do good'). Since they do come with fuses fitted, it's an 'inconvenience' of a just couple of minutes work and a few pence, but the argument is essentially the same.

I liked your first reply - in both senses - and was surprised ....

I gave an appropriate reply, saying that, in the context of a TV (which almost certainly has internal fuses), "It doesn't really matter" (what size fuse is in the plug).

But what if it hadn't been a TV? What if someone had said that they had just acquired some small electronic box of tricks, which needed 20W, 50W or 100W and wanted 'confirmation' that he should put a 10A (or even 13A) fuse in the plug, would you have really expected me to just say "yes, that's fine"? Would you have given that reply?

... but then you reverted to prevaricating mode or is it playing Devil's advocate as you say you sometimes.

I don't think it can reasonably be called either prevarication or 'playing Devil's Advocate', since I merely honestly reported what I personally actually do. I didn't start this, and wouldn't have said anything more if someone else hadn't ... big-all wrote that he had always used the smallest fuse size appropriate to the load, and I responded by saying that is what I do as well - which is, in general, the truth. We then got (yet again!) into the "Why?" discussion, and, as you know, my basic response is "Why not?", if it takes me only a couple of minutes and a few pence and just conceivably ('1 in millions' or whatever) might 'do some good'.

I suppose that, in my case, there's also the matter of history. When I first became exposed to BS1363 plugs (I wasn't 'brought up' on them!), it was 'drummed into me' that one should use the smallest adequate-sized fuse - so that's what I've 'always' done.

As I said before, if millions of people buy Lottery tickets every week, on the basis that is is 'not impossible' (even though incredibly unlikley) that they will win the jackpot, then I don't think what I do is any 'worse' - and they are paying £2 per go, not 'virtually nothing'!

Kind Regards, John

 

[EFLImpudence]

Indeed we are, but you went further than that and said of that 'something' ... "as you say, it may as well be the smallest", so you presumably agree with that as well?

Yes, but only if you have one.
There's no point specifically going out to buy one.
Also, in customer's houses because the next person who sees it may not understand.

As I keep saying, it's not a question of "doing some good", since the chances of it ever 'doing good' are extremely small, but that is is conceivable that it might one day 'do good'. If plugs came without a fuse fitted, I would say that it would be a no-brainer - if I had to reach into my store cupboard, grab a fuse and put it into the plug, why on earth would I choose a 10A or 13A one when a 3A (or maybe even 1A) one would be adequate

The 10A and 13A are adequate.

(and 'might just conceivably' one day 'do good').

I don't see how.

I gave an appropriate reply, saying that, in the context of a TV (which almost certainly has internal fuses), "It doesn't really matter" (what size fuse is in the plug).

Therefore, neither does it matter for other things.

But what if it hadn't been a TV? What if someone had said that they had just acquired some small electronic box of tricks, which needed 20W, 50W or 100W and wanted 'confirmation' that he should put a 10A (or even 13A) fuse in the plug, would you have really expected me to just say "yes, that's fine"? Would you have given that reply?

It depends on the cable, doesn't it?
Presumably the manufacturer would have fitted an appropriate fuse.

I didn't start this,

I have noticed you say that quite often when people are 'discussing' things with you.
It's not really relevant when you keep replying.

it was 'drummed into me' that one should use the smallest adequate-sized fuse - so that's what I've 'always' done.

I think that says it all.

As I said before, if millions of people buy Lottery tickets every week, on the basis that is is 'not impossible' (even though incredibly unlikley) that they will win the jackpot, then I don't think what I do is any 'worse' - and they are paying £2 per go, not 'virtually nothing'!

...but winning the lottery IS possible; lots of people HAVE done it.
There are lotteries in non-British parts of the world.

 

[JohnW2]

Yes, but only if you have one. There's no point specifically going out to buy one.

Fair enough. Given the extremely small chance that it would ever 'make a difference', I can accept that approach.

Also, in customer's houses because the next person who sees it may not understand.

I'm not so sure about that. People vary, so it can work either way. After all, this very thread was started by the OP because he was concerned when he found a 10A fuse in a plug supplying a load probably no more than an amp or two.

Therefore, neither does it matter for other things.

As I keep saying, it could conceivably 'matter' if, unlike a TV, the 'other things' did not have appropriate internal fusing.

It depends on the cable, doesn't it? Presumably the manufacturer would have fitted an appropriate fuse.

Never presume/assume Are you really saying that, if, say, someone posted a message saying that they had just bought a secondhand device which consumed 50W but which didn't have a fuse in the plug, and wanted 'confirmation' that they should put a 13A fuse into it ('because it is a 13A plug'), you would simply say "Yes, that's fine" (maybe after enquiring about cable size), without any qualification or other comments?

...but winning the lottery IS possible; lots of people HAVE done it.

Indeed they have. You obviously think that the chances (I would normally say 'probability', but changed just for you!) of using a lower-rated fuse ever 'making a difference' is less than 1 in 14 million (or whatever), and I'm far from sure about that.

Kind Regards, John

 

[EFLImpudence]

I'm not so sure about that. People vary, so it can work either way.

No, I mean I would fit a 3A in the customer's house as they, or someone else, may not understand.

As I keep saying, it could conceivably 'matter' if, unlike a TV, the 'other things' did not have appropriate internal fusing.
Never presume/assume Are you really saying that, if, say, someone posted a message saying that they had just bought a secondhand device which consumed 50W but which didn't have a fuse in the plug, and wanted 'confirmation' that they should put a 13A fuse into it ('because it is a 13A plug'), you would simply say "Yes, that's fine" (maybe after enquiring about cable size), without any qualification or other comments?

I refer the honourable gentleman to the references to the rest of the world.

You cannot argue (without blatant jingoism) that something that is only possible in the British parts of the world is 'necessary'.

 

[JohnW2]

No, I mean I would fit a 3A in the customer's house as they, or someone else, may not understand.

Oh, I see. Sorry, I misunderstood. However, you still haven't answered my question as to how you would respond to an OP in this forum who asked for 'confirmation' that he should put a 13A fuse in the '13A plug' that was supplying a 50W load.

I refer the honourable gentleman to the references to the rest of the world. You cannot argue (without blatant jingoism) that something that is only possible in the British parts of the world is 'necessary'.

No, one couldn't argue that. However, one could argue that those in other parts of the world are missing out on a potential (albeit extremely small) advantage that only exists when it is possible.

Kind Regards, John

 

[EFLImpudence]

Oh, I see. Sorry, I misunderstood. However, you still haven't answered my question as to how you would respond to an OP in this forum who asked for 'confirmation' that he should put a 13A fuse in the '13A plug' that was supplying a 50W load.

An inspection lamp springs to mind.

Well, I probably wouldn't bother getting involved in an explanation which may explain the belief that it was actually needed when the reply was "A 3A will do" but that doesn't mean it will do any good.
It depends on the cable - and more involved, the likelihood of overload and whether the fault current is covered.

No, one couldn't argue that. However, one could argue that those in other parts of the world are missing out on a potential (albeit extremely small) advantage that only exists when it is possible.

You could (and do) argue that but I, and presumably they, don't think it is valid.


I've just thought:

Do you think in the past that British manufacturers actually did rely on the knowledge that their customers could fit 3A fuses so they instructed that that should be done rather than protect their products sufficiently?
Now that production is for world-wide markets it really is no longer a valid argument.

 

[JohnW2]

... "A 3A will do" but that doesn't mean it will do any good.

If you had been asked to 'confirm' that a 13A fuse should be put into the '13A plug' and you replied (as I suspected you would, one way or another) "a 3A will do", wouldn't you be closer to what I have been saying than to the view you've been expressing?

You could (and do) argue that but I, and presumably they, don't think it is valid.

Goodness knows what "they" think, but nothing impossible, and I would expect that the chances of a lower-rated fuse sometimes/occasionally minimising the damage to some piece of equipment would be greater than that of winning the Lottery jackpot. Returning to the OP, one might ask why they put a 10A fuse into the plug for a TV which very probably would have been fine with a 3A one, particularly given that 10A is not even a BS1362 'preferred value' - it's not as if 10A fuses are cheaper!

I've just thought: Do you think in the past that British manufacturers actually did rely on the knowledge that their customers could fit 3A fuses so they instructed that that should be done rather than protect their products sufficiently?

Perhaps. The problem surely is that "protect their products sufficiently" is far from well-defined - and, whatever they decide is 'sufficient' does not mean that no-one would feel inclined to go beyond that 'minimum requirement' and provide 'even greater protection'. A different "they" have decided that we have to have 30mA RCDs protecting all sorts of things 'to save lives'. They presumably must regard that degree of protection as 'sufficient', but that doesn't necessarily mean than 20A, 15A or 10A ones wouldn't 'save more lives'.

Kind Regards, John

 

[stillp]

As I keep saying, it could conceivably 'matter' if, unlike a TV, the 'other things' did not have appropriate internal fusing.

Don't forget the let-through energy is a lot less for smaller fuses.

 

[JohnW2]

Don't forget the let-through energy is a lot less for smaller fuses.

Indeed. What makes you think that I am 'forgetting' that?

Kind Regards, John

 

[stillp]

I²t doesn't often get mentioned when fuse ratings are discussed on here.

 

[JohnW2]

I²t doesn't often get mentioned when fuse ratings are discussed on here.

That's true. However, it's part of the reason why I still believe that there will be occasions (perhaps rare) in which a smaller fuse will result in less damage (as the result of some fault {everyday sense}) in equipment downstream of the fuse.

The potential 'good' is, I agree, not often going to be realised - since, by the time a faulty piece of equipment has generated enough current to operate any OPD it is very frequently going to have been 'damaged beyond cost-effective repair' (one possible exception being when input filter capacitors go short-circuit) - but, as I keep telling EFLI, that does not mean that such will always be the case (such that the fuse has 'done no good).

I remain of the view that if it costs little or nothing more (in time/effort or pence) to fit an appropriate 'smaller' fuse, then "why not?", if there is an outside chance that it just might, one day, 'do good'.

Kind Regards, John