Maybe you should have asked them why they were making flaky equipment without the necessary protection intrinsic to the device.
Appliance fuses
- Thread starter Ray Tay
- Start date
Sponsored Links
I wish The Normans would give us back our country.
Too late - we assimilated them. They became us.
Sponsored Links
D'oh!
I can't help but ask ....
... if we really believe the concept that an OPD is there only to protect the cable, regardless of what the cable may be connected to, why is it that virtually everyone here (including myself) regularly advises those who want to run lighting off, say, a 32A-protected circuit circuit that they should install an FCU with a 3A fuse - given that we are usually talking about Method C 1mm² (or even 1.5mm²) cable, for which a 13A fuse would be adequate/appropriate.
Kind Regards, John
... if we really believe the concept that an OPD is there only to protect the cable, regardless of what the cable may be connected to, why is it that virtually everyone here (including myself) regularly advises those who want to run lighting off, say, a 32A-protected circuit circuit that they should install an FCU with a 3A fuse - given that we are usually talking about Method C 1mm² (or even 1.5mm²) cable, for which a 13A fuse would be adequate/appropriate.
Kind Regards, John
Hypothetically if I had a basic 900W heater that draws just under 4A, a 3A fuse is clearly inadequate so based on the previous comments on this thread, it would be reasonable to assume a 13A fuse was installed by the manufacturer in the appliance’s plug. Assuming a suitably rated mains lead was used, this lead would be protected by the fuse.
Now assume a metallic object finds its way into the heater and rests across the bare heating element in such a way as to short circuit some of the heating wire, reducing its effective length and hence increasing the current flow. In this hypothetical fault, the current increases to say 13A, the output of the heater is therefore more than tripled due to the fault and the heater's wire glows red hot. Assuming that this doesn't cause the element to burn out, this situation will continue almost indefinitely and could reasonably result in a fire.
In that example, had a lower rating fuse, say a 5A, been fitted it would only allow this overload for a limited time, which would limit the heat build up and may prevent the fire from starting.
In another hypothetical example, a bearing in a 4A appliance fails causing a motor to be overloaded which draws increased current, say 13A which is enough to heat the failed bearing and motor windings to the point of combustion. Again, a 13A fuse will not prevent this overheating, whereas a 5A fuse may prevent a fire.
The above scenarios are not beyond possibility, but I concede they are unlikely to occur in such a way as described. There should also be various other safety devices such as thermal fuses that should protect the appliance itself - however I have personal experience that such devices don't always work.
I understand that the main job of the fuse in the plug is to protect the lead to the appliance and assuming a suitable lead is used, a 13A fuse will perform this function. I remember noting that the mains lead of the charred remains of my tumble dryer was not damaged.
However, perhaps as a ‘bonus’ the fuse is also providing a degree of (what should be additional) protection to the appliance itself. Whether this is intentional or not, the protection is still there. In the above scenarios, a suitable but lower rated fuse may, in some specific circumstances have prevented a fire where a 13A fuse may not have done.
So I think there are valid engineering reasons why reducing a plug fuse size could at least be considered. As already mentioned, there are also disadvantages such as nuisance failure too.
Now assume a metallic object finds its way into the heater and rests across the bare heating element in such a way as to short circuit some of the heating wire, reducing its effective length and hence increasing the current flow. In this hypothetical fault, the current increases to say 13A, the output of the heater is therefore more than tripled due to the fault and the heater's wire glows red hot. Assuming that this doesn't cause the element to burn out, this situation will continue almost indefinitely and could reasonably result in a fire.
In that example, had a lower rating fuse, say a 5A, been fitted it would only allow this overload for a limited time, which would limit the heat build up and may prevent the fire from starting.
In another hypothetical example, a bearing in a 4A appliance fails causing a motor to be overloaded which draws increased current, say 13A which is enough to heat the failed bearing and motor windings to the point of combustion. Again, a 13A fuse will not prevent this overheating, whereas a 5A fuse may prevent a fire.
The above scenarios are not beyond possibility, but I concede they are unlikely to occur in such a way as described. There should also be various other safety devices such as thermal fuses that should protect the appliance itself - however I have personal experience that such devices don't always work.
I understand that the main job of the fuse in the plug is to protect the lead to the appliance and assuming a suitable lead is used, a 13A fuse will perform this function. I remember noting that the mains lead of the charred remains of my tumble dryer was not damaged.
However, perhaps as a ‘bonus’ the fuse is also providing a degree of (what should be additional) protection to the appliance itself. Whether this is intentional or not, the protection is still there. In the above scenarios, a suitable but lower rated fuse may, in some specific circumstances have prevented a fire where a 13A fuse may not have done.
So I think there are valid engineering reasons why reducing a plug fuse size could at least be considered. As already mentioned, there are also disadvantages such as nuisance failure too.
That may be so, but some alarm panels as has been mentioned recommend a 2 Amp fuse in the FCU that is supplying them. I just used a 2 Amp fuse instead of a 3 Amp one in the FCU as a extra course of protection along with the internal and non replaceable T 2A Fuse, even if it only adds 0.001% extra protection. I had plenty of Spare BS1362 2 Amp fuses anyway when installing the system.
I accept .
I would say that is because of the generally accepted view that, for whatever reason, lighting and lighting circuits are protected by 6A OPDs.
I, quite frequently in those examples, think I may add that if the circuit is run in 2.5mm² then no fusing is required but this would lead to discussions that the lighting products are only 6A or 10A even though fitted with lamps of low wattage and each item cannot be overloaded.
Anyway, why are lighting circuits 6A with 1mm²?
Also, DIYers cannot check the Zs and fault current on their spurs.
Similarly, I do not like to advise connecting ovens with less than 32A cable but you often say it would be impossible for the short connection not to comply with the fault current requirement.
All but impossible and it would cause the element to melt.
Does the element not get red hot in normal use?
Assuming it did happen, why would a hot element cause a fire.
That is one reason given sometimes for extractor fans requiring the 3A fuse.
However, that would be the manufacturer's neglect in designing the product badly.
You say that and it sounds good but are there any examples?
Well, there presumably aren't or Europe, America and the rest of the world would be going up in smoke.
What do they "recommend" in countries where there are no such things as FCUs?
Maybe, but that really begs a similar question/point. If it is felt that a 6A OPD is necessary, that presumably must be because the OPD is being expected to 'protect' something other than just the cable??
I'd certainly say 'virtually impossible' in a 'normal house', wouldn't you?
Kind Regards, John
Yes, but, as in the rest of the thread, I don't think that is a genuine expectation.
The accessories and pendant drops may be 6A but they only carry the current to individual items.
I would, but we can't tell from here.
The circuit may be otherwise inadequate.
I started the post by saying this was a hypothetical situation, there is no real appliance. It is a description to show the engineering reasoning of how a lower fuse rating may, in some circumstances, provide additional protection. I also specifically said "assuming that this doesn't cause the element to burn out". In this abstract context, what the element does in normal use is not relevant, the point is that a substantial overload could occur indefinitely with the 13A fuse and that such an overload "could reasonably result in a fire".
The idea is consider the principle not any specific device. I am saying that preventing a substantial overload would limit heat build up and in so doing, may prevent a fire from occurring. If you want to think about the element example, perhaps plastic components of the heater that normally stay cool melt under the fault condition and drop on to the element which then causes a fire.
Yes, I completely agree. However coming back to real appliances in the real world, I have personal experience of an appliance that became faulty, the internal safety mechanism(s) failed to prevent an unsafe condition, the 13A plug fuse did not blow and the appliance caught fire which set fire to the house. When you say the fault I describe is "All but impossible" you are saying that it is possible, just unlikely and I agree. The total number of fires attended in the UK in 2013-14 was 212,500, 19% were dwelling fires so 40,375. With a population of about 64 million making the chance of a dwelling fire about 1 in 1,600 - and not all of those were caused by electrical appliances. So thankfully fires are not that common and whilst I agree the situation I describe is unlikely, there is still the possibility that it will occur and it happened to me. Winning the lottery jackpot is also an unlikely event, but but people still buy Lottery tickets and people do win jackpots. That has not happened to me btw!
It sounds like you do agree after all
. Examples I'm not so sure about as you cannot prove a negative. Do appliances sometimes become faulty and catch fire? Yes, that is a fact. Will a more closely matched fuse provide better protection against overloading and hence reduce the risk of fire? There are good engineering reasons to argue that would be the case in some circumstances. Where more closely matched fuses have been used have fires been prevented? This is more difficult to answer, a blown 5A fuse does not mean the appliance would have caught fire had a 13A fuse been fitted, but equally there is still a small possibility that it may have done.Electrical fires do occur in Europe and I have read that the US do have more electrical fires, but mainly due to the higher currents used due to the 110V supply and also the common use of aluminum wiring. So excluding the US due to the voltage difference, does Europe have more electrical fires, is it due to the different electrical system design, are there other influencing factors - not easy to answer. This document "Comparison of European Fire Statistics Final report for the Department for Communities and Local Government Fire research report 1/2012" probably gives more information but from a very brief look it seems to be saying the influencing factors and vastly differing ways in which data is collected makes a meaningful comparison difficult.
http://webarchive.nationalarchives....es.gov.uk/documents/corporate/pdf/2159418.pdf
Last edited:
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
