fuse for extractor fan
- Thread starter nick9one1
- Start date
Sponsored Links
Good point. I sort-of misread (or 'mis-thought about') what you'd written, and was trying to think of a way it could be wired which would not result in the switch isolating both L and S/L, not the issue about fusing to which you refer.
So, yes, I agree that with just the wiring that had previously gone to/from an isolator, one could not swap it for one of those isolator+fuse thingies and have both L & S/L protected by the fuse.
Kind Regards, John
Indeed, as has been said, if one really wants to add a fuse, it has to be upstream of the light switch.
Not in the minds of those who want to be able to isolate just the fan (leaving lights working), whilst the fan is fault or whilst one is working on the fan (as well as having the upstream fuse).Which completely negates the need for a three pole isolator!
Kind Regards, John
Sponsored Links
As has very often been said, if the manufacturers really feel that the product requires 'tight' protection (0.5A or whatever), then that should be provided internally within the product, leaving the circuit's OPD to protect the fixed wiring of the circuit!
Having said that, I seriously struggle to think of what useful purpose such 0.5A (or whatever) protection would serve.
I never have, and never will, provide any of these fans with a fuse as 'required' by manufacturers!
Kind Regards, John
I'm sure that I posted these a year or two back but, for anyone interested, below typical circuits (two diagrams) of these things, mainly ascertained at 'autopsy'! As can be seen, they are all very similar, the Wickes one being slightly different, in having an (essentially unnecessary) transistor.In this case: ,annotated photo of a fan timer module> (Not my work!) ... the switched live goes through the 270k resistor and a 15V zener before reaching the logic circuit. Theoretically, no need for a fuse
Kind Regards, John
Pretty sure it's a click minigrid 3 pole fan isolator module plus a click minigrid fuse module on a 3 module click minigrid plate.
You could put the fuse before the lightswitch, this would mean that both the light and the fan were protected by the fuse but I don't see that as a problem.
You could also build a plate with a fan isolator and two seperate fuse modules using minigrid, but that would require a double backbox.
Sorry, my point was that if there were to be a single fuse to protect both L and SL, you will only ever need a two pole isolator.
To have a three pole isolator and a fuse in one unit, as in this context, seems senseless!
Yes, that was pointed out to me.
Yes, both sparkwight and myself have suggested that - not that I (nor, I suspect, he) think that there is any point in any such 'additional fusing down'!
Yes, one could - but, as also has been said, that would mean that if just one of the fuses blew (and/or was removed) with the isolator switch still 'on', then some parts within the fan enclosure would remain live, which wouldn't be a terribly clever/safe situation.
To simply forget about this silly 'fusing down' seems to be the simplest solution, leaving one just having to decide whether or not one wants the (very occasional) 'convenience' of having a 3-pole isolator (since a 'very very occasional convenience' is really all it offers)!
Kind Regards, John
Only if one is happy to have to lose the light when 'isolating' the fan. If one want to have the fuse (priotecting both L and S/L) AND to be able to isolate just the fan, then one has to have the fuse and isolator 'in different places' (electrically),, not within the same 'unit' - which is perhaps your point, since you go on to say ....
Kind Regards, John
Bernard posted a diagram in another thread.
As can be seen in the diagram the fuse *does* connect directly to one of the poles on the isolator.
I suggest implementing this by using the isolator/fuse plate as the junction box. The light, switch and fan can then be connected to the isolator/fuse plate using normal T&E and 3+E cables.
As can be seen in the diagram the fuse *does* connect directly to one of the poles on the isolator.
I suggest implementing this by using the isolator/fuse plate as the junction box. The light, switch and fan can then be connected to the isolator/fuse plate using normal T&E and 3+E cables.
Yes, that was what I meant, but again, sorry John
I was tied up with the original diagram in post #3 and couldn't immediately see where the 3 pole isolator would go to make sense.
And I was just about to post my X marks the spot picture, when plugwash beat me to it!
He did.
It does, and I don't think anyone (certainly not I) have suggested otherwise - but, as you go on to say ...
Indeed - but, as sparkwright said, as a 'retrofitting' exercise, that involves appreciable 're-wiring' (i.e. if being done on an existing installation).
As I've said, I really cannot get myself interested in fitting these fuses - and, if one doesn't use them, then life become much more simple, even if one wants an isolator ('for very occasional convenience').
Whoever thought up that 'isolator + fuse' combination of modules probably had not "thought it through" (any more than I did, initially
).Kind Regards, John
Alternative options involving less rewiring would include,
1. Disconnect the feed cables from the light and use a JB to attach them to a new cable running to the fuse/isolator plate. Then use the existing 3+E to take fused live and neutral from the fuse/isolator to the light and switch (via the light) and bring switched live back.
2. Replace the switch drop with 3+E and locate the fuse at the lightswitch rather than at the fan isolator.
3. Locate the fuse separately from either the fan isolator or the light.
4. Cut out a larger box at the fan isolator location and fit two fuses.
Fair enough, we all have to decide to what extent we will follow manufacturers instructions and to what extent we will accept responsibility for the consequences of deviating from them.
IMO it does have legitimate uses, but selling it as a pre-assembled combination with no instructions and no indication that it is in most cases *NOT* a drop-in replacement for a regular fan isolator leads to a high probability of only one of the two live feeds to the fan ending up fusedWhoever thought up that 'isolator + fuse' combination of modules probably had not "thought it through" (any more than I did, initially
Surprisingly It seems that Scolmore Click themselves are now selling these pre-assmbled I'm sure that didn't used to be the case.
Yep, all possibilities, but (1) and (2) represent significant re-wiring'. As I've said, if I really wanted (or 'was being forced to')add a fuse, I would almost certainly do (3)
As has been discussed, it can be argued that such would be potentially dangerous.
Indeed. I really see no electrical consequences (of not adding the fuse) that I would ever have to 'accept responsibility' for, but I've acknowledged that there could conceivably be hassle dealing with a manufacturer who was (unreasonably) 'trying it on' in relation to a warranty claim.
Agreed. However, the 'legitimate uses' are probably so relatively rare that it would be better to let people put modules together themselves in such situations, rather than selling such an item 'pre-assembled', with the risks you describe.IMO it does have legitimate uses, but selling it as a pre-assembled combination with no instructions and no indication that it is in most cases *NOT* a drop-in replacement for a regular fan isolator leads to a high probability of only one of the two live feeds to the fan ending up fused
Kind Regards, John
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
