Why don't lamps come with a 1 amp fuse in the plugs?
- Thread starter eveares
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I wouldn't, but I don't believe for a moment that such would be the case.
I can't say that I've got any incandescent lamps protected by 1A fuses these days - but, although I do use a fair number of 1A ones (mainly for trivial 'electronic' loads) I have very rarely, if ever, had to replace one of them.
Your guess is as good as mine. One imagines that replacement of (thermally or mechanically) damaged ones is probably the most common reason but, beyond that, I really don't know. However, the amount of 'shelf space' given to them in the sheds etc. suggests that there must be a pretty significant market.
Kind Regards, John
Mum once plugged two 2Kw heaters into a normal extension lead 
while I was out. The lead of course got very hot but the 13 amp fuse in the plug did not blow?
Why was this, surely 17 amps through the fuse should of caused it to blow!
My guess is it was a faulty fuse, i wonder how many fuses are faulty?
while I was out. The lead of course got very hot but the 13 amp fuse in the plug did not blow?Why was this, surely 17 amps through the fuse should of caused it to blow!
My guess is it was a faulty fuse, i wonder how many fuses are faulty?
Mum once plugged two 2Kw heaters into a normal extension lead
Why was this, surely 17 amps through the fuse should of caused it to blow!
My guess is it was a faulty fuse, i wonder how many fuses are faulty?
no quite normal 50% surge would probably blow it 25% over not unusual
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It would take a long time (probably well over an hour) for 17A to blow a 13A fuse. If it were a (hypothetical) 13A Type B MCB it would take up to an hour to operate at ~19A.Mum once plugged two 2Kw heaters into a normal extension lead
As for 'faulty fuses', it's obviously impossible to test the desired functionality non-destructively, so one is reliant on sample testing from batches - in which case the occasional rogue one is bound to get through.
Kind Regards, John
A3 amp fuse is probably safer than the method used elsewhere in the world including the rest of Europe and the USA. They don't have any fuses at all in the plugs and rely on a 10A or 15A MCB in the supply to the sockets.
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Flexible cables sizes.
0.5mm² = 3A
0.75mm² = 6A
1mm² = 10A
1.25mm² = 13A
Since only require a fuse to protect a cable only 3, 6, 10, and 13 amp fuses are required. Oddly you can buy 1, 2, 3, 5, 7, 10 and 13 seems some one forgot 6A was rating for 0.75mm² flex?
As an apprentice 5 and 13 were the sizes carried but as time went on 3 and 13 replaced the stock as for 0.5mm² 5A is too big.
and the IEC 60320 C3/4/5/6/7/8
are rated at 2.5A this includes Clover-leaf used with computers since you can't get a 2.5A fuse to fit in a British plug it follows we either have to use a 2 or 3 amp fuse. C11 - 18 are rated 10A and clearly fitting a 3A fuse in a kettle it is too small and 13A is over rating of the C15/16 connectors used with many kettles.
But many years ago I taught my children how to select a fuse. I showed them the watts rating and explained for with heating it could be as rating so 750W was 3A and for a motor you went to next size so 750W was 5A with an electric drill. They had gone around the house checking fuses under my watchful eye and ensured right fuse was in every appliance.
About 6 months latter they were taught in school how to wire a plug and select a fuse which resulted in me having to visit the school when my kids where telling the teacher he had it all wrong. And the teacher was not totally wrong but had simplified the selection process.
And the point is we have to have a simple method which can be taught in schools. I am sure some teachers call it 250v others 240v and some 230v as very likely they teach what was valid when they were taught.
My son came home laughing that his teacher said he was wrong when he said the two types of transistor were Field effect and Bi-polar the answer was NPN and PNP. Clearly the teacher knew no better and with such a wide range that teachers have to cover one can understand the error.
So at least teaching below 750W = 3A and above = 13A is easy for school teachers to remember and teach.
0.5mm² = 3A
0.75mm² = 6A
1mm² = 10A
1.25mm² = 13A
Since only require a fuse to protect a cable only 3, 6, 10, and 13 amp fuses are required. Oddly you can buy 1, 2, 3, 5, 7, 10 and 13 seems some one forgot 6A was rating for 0.75mm² flex?
As an apprentice 5 and 13 were the sizes carried but as time went on 3 and 13 replaced the stock as for 0.5mm² 5A is too big.
But many years ago I taught my children how to select a fuse. I showed them the watts rating and explained for with heating it could be as rating so 750W was 3A and for a motor you went to next size so 750W was 5A with an electric drill. They had gone around the house checking fuses under my watchful eye and ensured right fuse was in every appliance.
About 6 months latter they were taught in school how to wire a plug and select a fuse which resulted in me having to visit the school when my kids where telling the teacher he had it all wrong. And the teacher was not totally wrong but had simplified the selection process.
And the point is we have to have a simple method which can be taught in schools. I am sure some teachers call it 250v others 240v and some 230v as very likely they teach what was valid when they were taught.
My son came home laughing that his teacher said he was wrong when he said the two types of transistor were Field effect and Bi-polar the answer was NPN and PNP. Clearly the teacher knew no better and with such a wide range that teachers have to cover one can understand the error.
So at least teaching below 750W = 3A and above = 13A is easy for school teachers to remember and teach.
3 amp x 230v (official UK voltage) = 690 watts not 750 watts (690w commonly round up to 700w). Same goes for 13 amp being rounded up from 2990w to 3000w
Also I would not want a 13 amp fuse in 1KW appliance fed by 1mm² cable; thus they need to teach that 5 amp is sometimes needed as 3 amps is to low and 13 amps is to high.
Also a lot of teachers (especially at secondary school level) only know what they need to teach of the syllabus, i.e I was never taught ohms law at school what I think should be.
Also I was once taught in a ICT lesson that a drive (i.e. cd drive) and a driver (i.e. software to make hardware work) were the same thing!
Not really - 3A at 240V is 720W. The same resistive appliance at 230V will be 662W.
You have to use the voltage quoted by the manufacturer or convert the power.
I don't think rounding up comes into it.
What does that prove?
A 3000W @ 240V heating element is 12.5A. At 230V it will be 12A.
Are things made or measured that accurately?
But not in this case (if talking about flex). 1kW @ 240V is 4.17A. What danger is there?
What about the English teacher?
We didn't do such things. It hadn't been invented.
It was where you parked the car and the person who did it. Cue winston.
Does that not depend upon the nature of "the 1kW appliance"? If the load were not one which was considered 'unlikely to create an overload' (note the double negative!), then there would be a theoretical issue with 1mm² flex protected by a 13A fuse, wouldn't there?
Kind Regards, John
I was referring to the amount of power a 3/13 amp fuse can take at 230v, not the fact that an appliances power and current consumption decreases as the voltage goes down to the point of where the current goes below the fuses threshold.
I don't think it takes a genius to understand that a appliance that is rated at 240v will consume less than it's rated current and thus less power at 230v - Ohms law.
I simply took the fuse rating and multiplied it by the official UK voltage. whether BS1362 fuses rated are 230 or 240v should not matter as they are current dependent and not power dependent right?
The cable size being ok for 1kW was not what I was referring to, 1Kw is more suited to a 5 amp fuse than a 13 amp fuse - that was my point.
That would be true but what is this 1kW load which could do that (in the home?)?
It doesn't. However, it might require a little bit more 'genius' to understand that Ohm's Law only applies to 'dumb resistive' loads. With the more intelligent loads that we are increasingly seeing (e.g. those powered by a SMPSU), a decrease in supply voltage will actually lead to an increase in current (and little change in power).
Kind Regards, John
A vacuum cleaner or similar, something like a 1kW fan heater, a good few DIY power tools etc. etc. (the common feature in all those examples being the presence of a motor which could jam)?
Kind Regards, John
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