Because BS 7671 specifically states that your traditional ceiling rose should not be connected to a circuit with a protective device exceeding 16A.
Obviously a 13A fuse is fine if the cable is protected by it.
Appliance fuses
- Thread starter Ray Tay
- Start date
Obviously a 13A fuse is fine if the cable is protected by it.
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Right.
...but it would.
I don't think it could occur - let alone indefinitely.
...but you counter my argument by saying it's only hypothetical.
Fair point - then the element will melt.
Would an element that can withstand 13A indefinitely be effective at its designed 4A rating?
No, I mean it sounds like a good idea but has no basis.It sounds like you do agree after all.
I disagree.
Apart from the flying piece of metal, the only overloads that can occur in such appliances are stalled motors.
I am sure the manufacturers are aware of this and make provision otherwise they would instruct lower fusing, albeit due to their ineffectiveness.
I think fires in such appliances are much more likely to be caused by the ignition of fluff etc. when fusing is irrelevant.
A traditional loop-in ceiling rose could carry the entire circuit current.
Ditto switches if looping there.
Ditto any compliant JBs.
In the same way as a socket may carry 32A?
Granted the loop has separate terminals.
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EFLImpudence -I think you are getting caught up in the examples I used to explain the principle and you are thinking about a device rather than the principle. To keep purely to the principle, a device that normally draws say 4A could conceivably develop fault(s) where the current increases to say nearly 13A. At that point a 13A plug fuse will not disconnect the device, whereas a 5A plug fuse will. A faulty device consuming over 3x its normal power could overheat which could cause a fire.
I think you are saying that what I describe above is unlikely to occur for a number of reasons and I agree! In real life the overload would probably not cause enough heating to cause a fire, or would be so large as to break the element, or blow a 13A fuse and the appliance should have other protective devices, etc, etc. In the situation I am describing all of these things happen to fail in a particular way as to lead to the situation described. Yes it is very unlikely, but so is winning the lottery jackpot and that does happen, just as what I describe could happen.
Returning from the principle to real life, I had an appliance where the protection failed and it caught fire. Yes, it may have been ignition of fluff, but shouldn’t an appliance such as a tumble dryer that produces fluff be designed not to set fire to the fluff!? Of course it should, but in my case something went wrong which lead to it catching fire which should never have happened – but it did.
The manufacturer was unable to do an ‘autopsy’ of the device, so the root cause is not known in this case, however in your words fluff was the “more likely” cause, meaning there are other possible causes. One of the other possible causes is an overload that did not blow the fuse. The fire is a fact, the cause is unknown. I agree fluff is the more likely cause, but neither of us know the actual cause and saying that something is unlikely means that it is possible.
When you say you disagree, rather than arguing with my examples, what is the principle behind your argument? Are you saying that a faulty appliance will always, unequivocally and without fail disconnect itself in a safe way when a 13A fuse is fitted when a lower one could have been used? Appliance fires are a fact, are you saying that all appliance fires ever, past and future could never be prevented by using a better matched fuse in the plug? Would you personally guarantee that by betting yours assets, i.e. house(s) and car(s) etc. on that fact?
I think you are saying that what I describe above is unlikely to occur for a number of reasons and I agree! In real life the overload would probably not cause enough heating to cause a fire, or would be so large as to break the element, or blow a 13A fuse and the appliance should have other protective devices, etc, etc. In the situation I am describing all of these things happen to fail in a particular way as to lead to the situation described. Yes it is very unlikely, but so is winning the lottery jackpot and that does happen, just as what I describe could happen.
Returning from the principle to real life, I had an appliance where the protection failed and it caught fire. Yes, it may have been ignition of fluff, but shouldn’t an appliance such as a tumble dryer that produces fluff be designed not to set fire to the fluff!? Of course it should, but in my case something went wrong which lead to it catching fire which should never have happened – but it did.
The manufacturer was unable to do an ‘autopsy’ of the device, so the root cause is not known in this case, however in your words fluff was the “more likely” cause, meaning there are other possible causes. One of the other possible causes is an overload that did not blow the fuse. The fire is a fact, the cause is unknown. I agree fluff is the more likely cause, but neither of us know the actual cause and saying that something is unlikely means that it is possible.
When you say you disagree, rather than arguing with my examples, what is the principle behind your argument? Are you saying that a faulty appliance will always, unequivocally and without fail disconnect itself in a safe way when a 13A fuse is fitted when a lower one could have been used? Appliance fires are a fact, are you saying that all appliance fires ever, past and future could never be prevented by using a better matched fuse in the plug? Would you personally guarantee that by betting yours assets, i.e. house(s) and car(s) etc. on that fact?
I don't think there are valid engineering reasons which would not have already been considered.
Of course I am getting caught up in the examples. That is what you used to justify your reasoning.
...but could it?
Have you an example where that will occur with the consequences you are worried about.
Theoretically yes but is it possible?
Could it? Example, please.
Due to the protection failing so - irrelevant to the argument.
The rest of your post seems to agree with me yet asks if I can guarantee that something never happens.
It is not necessary to fit smaller fuses than required.
I don't know what else to say.
Thank you! That is all I was getting at
.“Theoretically yes” has the definition that something is possible according to theory. As I have said before I think you are saying “will this happen in real life?” and as I have said before, it is unlikely, perhaps very unlikely but as you concede it is possible, in theory, for what I describe to occur.
To be clear I am not saying that it is necessary to fit smaller fuses, I am sorry if I gave that impression. I am simply giving clear, valid technical reasoning as to why fitting a smaller plug fuse may provide additional protection in certain circumstances. Assuming that standards are met, I agree that just because a small amount of additional protection may be available, it doesn’t mean that you have to do it – just look at some Chinese products, they take this to the extreme!
I’m not saying your statement is wrong, but you have made a statement with no justification and give no principle behind your argument. You need to explain, with valid technical reasoning the basis behind your view, rather than saying “could it…” to my reasoning and then stating something.
I think we have reached a consensus of understanding, but just in case you feel I haven’t fully answered your questions, you ask for an example twice, but I have already provided two examples in my previous posts which describe how the situation that I am explaining could occur; the heater and the motor. However you have already agreed that is theoretically possible, so I don’t think further explanation is needed.
Finally, yes I was asking you to guarantee that fitting a smaller fuse could never be beneficial. In a similar way that manufacturers guarantee (and are liable for) their products not breaking down or catching fire. Sometimes, despite all the design, testing and protection, faults and fires do occur and hence they have to pay out… I see you are not willing to put your money where your mouth is! Probably as you agree that what I describe could theoretically happen, which is a wise move!
Are you confusing theory and hypothesis?
http://www.oxforddictionaries.com/definition/english/theory
http://www.oxforddictionaries.com/definition/english/theory
If you think I have confused those two words, you have clearly misunderstood everything I and others have said.
Your own linked Oxford definition is appropriate here theory - "A supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained:"
If you agree that the theory of what I describe (with technical and scientific basis) is correct, I think we are on the same page. If you are saying that fitting an appropriate but lower than 13A fuse can never provide any additional protection to an appliance under any circumstances, then please do explain, with technical and scientific reasoning, why that is the case.
Whilst I am satisfied as to the validity of my points, I genuinely would like to read a solidly reasoned and well explained argument as to why the theory I have explained, with examples, is not correct. I suspect I will just get more of "could it..." and "I think this. Because."
Your own linked Oxford definition is appropriate here theory - "A supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained:"
If you agree that the theory of what I describe (with technical and scientific basis) is correct, I think we are on the same page. If you are saying that fitting an appropriate but lower than 13A fuse can never provide any additional protection to an appliance under any circumstances, then please do explain, with technical and scientific reasoning, why that is the case.
Whilst I am satisfied as to the validity of my points, I genuinely would like to read a solidly reasoned and well explained argument as to why the theory I have explained, with examples, is not correct. I suspect I will just get more of "could it..." and "I think this. Because."
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Are you always spoiling for an argument?
WTF are you on about?
Have you installed any of their stuff?
I strongly suspect not, otherwise you would know they are neither flaky nor without the necessary protection.
Please clarify your statement.
A smaller fuse provides more protection. That is obvious.
I have been saying that it is unnecessary and have been trying to get you to provide an example of when it would be necessary; not just theoretical scenarios.
Well, if the answer to "Could it?" is "No" then there is no point.Whilst I am satisfied as to the validity of my points, I genuinely would like to read a solidly reasoned and well explained argument as to why the theory I have explained, with examples, is not correct. I suspect I will just get more of "could it..." and "I think this. Because."
With some posts talking about fuses for alarm systems, I would not agree that a smaller fuse always provides more protection.
Oh bugger.
I have been trying to think of an analogy.
I seem to keep coming up with bullet-resistant glass.
If it is designed to withstand the projectiles from all the weapons which it encounters, then arguing that increasing its strength by 50% would offer more protection is true and sounds like a good idea - but it is not necessary.
Saying that a new weapon may be invented which would necessitate the strengthening is also true but it does not exist.
I seem to keep coming up with bullet-resistant glass.
If it is designed to withstand the projectiles from all the weapons which it encounters, then arguing that increasing its strength by 50% would offer more protection is true and sounds like a good idea - but it is not necessary.
Saying that a new weapon may be invented which would necessitate the strengthening is also true but it does not exist.
Yes, but I was not talking about a "protective device exceeding 16A". I was asking why, if we really believe that the OPD is only there to protect the cable, 'we' almost invariably advise people to use a 3A FCU to feed lighting from a 'higher rated' circuit (e.g. 32A) when a 13A fuse would almost always adequate to protect the cable . As you go on to say...
It may be "obvious" but it is very rarely advised.
Kind Regards, John
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