I am thinking about it in electrical terms, ignoring the instructions for now. It is just conceivable the 3A fuse on the permanent Line supply (i.e. what the motor runs off) might provide protection to the motor. The switch Line is just a signal wire, it does nothing else.
Extractor fan need 3 amp fuse
- Thread starter spiderplant0
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If it does it will have internal protection.
Yes. if the cable is appropriate.
Because they are not needed.
There you go, then.
I am simply saying what I would personally do given a similar situation, it is up to the OP to decide what they want to do.
They are not necessarily 'wrong' since the equipment to do what they suggest is commonly available and doesn't go against any regs. However I personally would think it is unnecessary to fuse the SL, and would be happy not to if it is not practical to do so.
They often include a none resettable thermal fuse. Not to protect the winding, but to prevent the windings catching fire.
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The live from the light switch may just be a signal line but it is capable of drawing sufficient current for the unit to overheat and catch fire. It wouldn't normally but then again, the permeant live would not short-out in normal circumstances either. I.e. the point of the fuse is to offer protection in all excess-current circumstances. E.g. if the motor were to fly apart and short out the power on the signal live or something. So I would argue that the fuse needs to cut of all potential sources of power from the device.
Anyway, from your comments I'm concluding that the 3 amp fuse doesn't offer much in extra safety, but may be necessary to comply with regulations.
BTW, my main concern would not be claiming on the price of the fan if it melted, but if the overheating fan burnt the house down and the insurance company quibbling that it was my fault as I hadn't wired the fan correctly.
Anyway, from your comments I'm concluding that the 3 amp fuse doesn't offer much in extra safety, but may be necessary to comply with regulations.
BTW, my main concern would not be claiming on the price of the fan if it melted, but if the overheating fan burnt the house down and the insurance company quibbling that it was my fault as I hadn't wired the fan correctly.
That's my approach
I regard the 'electrical argument as pretty simple. For a 3A fuse (in the permanent L supply to the fan) to blow, something must already have happened within the fan to cause at least 22A to flow - and it is very difficult to think of any faults that would cause that and still leave the fan operational. I would therefore think that the fuse would only blow if the fan had already 'died' - hence the same situation as if there had been no fuse.
I've already made that point - but, as above, by the time 22A (or more) has flowed through the motor, the situation would almost certainly have become 'unrecoverable'.
Kind Regards, John
Nothing is impossible, but it's very hard to envisage any situation in which that would occur (unless the entire timer module had already 'catastrophically failed' - e.g. 'burned up').
The S/L ('signal') input to the module invariably goes to just one place - via a high value (typically about 280 kΩ, sometimes as 'low' as 150 kΩ) resistor to trigger the electronics - so, unless something somehow managed to create some other path for current flow (or the resistor were to fail 'short-circuit', which would be incredibly unlikely), the greatest current that could flow into the S/L input of the module (even in the event of some 'short-circuit'within the module) would be no more than about 1.5 milliamps (i.e. 0.0015 A) at most.
No, not to 'comply with regulations' (which only require one to 'take account of' the manufacturer's instructions) but, rather, only to comply with those MIs.
I think you can be strongly reassured about that concern. The (probably 6A) protection of the circuit will save your house from being burnt down at least as well as any 3A fuse would/could. If you were worried about electrical things on 6A circuits catching on fire and burning your house down, you would have to worry about all your lights and light fittings, and maybe other things.
Kind Regards, John
Are you not thinking of a 13A fuse when considering 22A?
Are, yes, well spotted (I blame 'old age'
). My apologies.So, yes, for a 3A BS1362 fuse,it only requires (at least) 5-10A to blow it - so a bit less than what it would take to trip a B6.
However, when one realises that the normal running current of one of these fans is usually of the order of 30 - 90 mA, even 5A would represent at least 50 times (maybe well over 100 times) normal the running current - and if that had already happened before the fuse blew, it would be extremely likely that the fan would have been damaged beyond repair.
Kind Regards, John
Go and ask the maker if they sell the fan in other countries. Unless it's come with instructions in multiple languages, which would tell you the answer.
Good point/question. From a typical Manrose Installation Guide ...
.... although the document is only in English, the preceding instruction (as seen above) indicates that they acknowledge that the fan might be installed 'outside the UK (where they seem to think that "the I.E.E' exists
), they still 'require a 3A fuse. I wonder how someone outside of the UK is expected to implement that 'requirement'?Returning to all the fuss about failures to fully comply with MIs "invalidating warranties", what about 'requirements of MIs" such as these (again, from Manrose MIs ...
OR
Kind Regards, John
If the manufacturer instructions stated 'must be protected by a 3 amp fuse or 6 amp breaker' I could understand it, but requiring a 3 amp fuse in all circumstances regardless is just unreasonable.
It amazes me too how many installers have the attitude of "that's what the instructions say so that's what it'll have", thereby unncessarily complicating the installation. For me, the tenuous nature of 'invalidating warranties' just doesn't cut it.
It amazes me too how many installers have the attitude of "that's what the instructions say so that's what it'll have", thereby unncessarily complicating the installation. For me, the tenuous nature of 'invalidating warranties' just doesn't cut it.
Up to a point, I agree - but as people always say, if the manufacturers really believe that a certain degree of over-current protection would possibly spare their product from some damage, and therefore is 'necessary', then they really should provide that protection internally within their product.
Quite so. As I recent wrote, their requirement as usually written would 'require' a downstream 3A fuse even if (I know it won't happnen!) the circuit was, hypothetically, already protected by a 2A OPD.
In any event, in practical terms, I feel sure that the probability of a 3A fuse protecting anything that a 6A MCB wouldn't at least equally protect is pretty close to zero!"
I totally agree. Us Brits have somewhat of a reputation for 'blindly doing what we are told', but I'm not sure it would work quite the same in some other countries
I recall some of the early 'smoking bans' in France, which were responded to with little other than laughter by a fair proportion of the population Kind Regards, John
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I disagree with your reading of this.
You seem to be omitting the full stop, and new paragraph number 3.
Would this be clearer?
End________________________________________________________________________
Next
It hasn't existed here for 17 years..... although the document is only in English, the preceding instruction (as seen above) indicates that they acknowledge that the fan might be installed 'outside the UK (where they seem to think that "the I.E.E' exists
They can't. Which just proves that the maker is utterly clueless.
To my mind those are falsehoods which are egregious enough to be classed as lies, and therefore, in an ideal world, would see the directors of Manrose facing prison sentences.Returning to all the fuss about failures to fully comply with MIs "invalidating warranties", what about 'requirements of MIs" such as these (again, from Manrose MIs ...
OR
Kind Regards, John
And yes, I really do mean that.