Fuses for an extractor fan

[ban-all-sheds]

I'm going to be installing an extractor fan in my bathroom with either a timer- or humidity-overrun. I want it to be switched by the pullswitch that controls the electric shower, not the light. The instructions say there should be a fuse in the supply to the transformer, but the position assumes that the switch either controls the fan, or the fan + bathroom light, for it will have to carry the current for the latter as well. But substitute a shower for the light, and that fuse would need to be 40A, and might not do much to protect the fan transformer. Or the wiring thereto.

The solution I've thought of is to have 2 fuses after the fan isolation switch, one in each live. The switch will be outside the bathroom, so would panel fuseholders of this type:

mounted on a blanking plate be allowable?

Can the connections to the fuseholders be soldered, or must they be crimped?


Alternatively, does anybody know if I can get a 3- or 4-pole pull-switch?

 

[spark]

How is your wiring arranged at the moment for your shower? Surface mount or flush mount pull-cord? How will you run cables between all the accessories? Loft space or not? I have a better idea for you but need as much info as poss to see if it's viable.

 

[breezer]

to do what you propose you would have to run the SAME size cable (that feeds the shower) from the pull cord to your fan (ok so you will have a fuse) but you can not get 2 X 6mm or 2 X 10mm cables into a pull cord,

Also the fuse holdes you show could not be connected to a 6 or 10mm cable

 

[spark]

not necessarily...

 

[ban-all-sheds]

spark How is your wiring arranged at the moment for your shower? Surface mount or flush mount pull-cord? How will you run cables between all the accessories? Loft space or not? I have a better idea for you but need as much info as poss to see if it's viable.

The wiring runs in the loft, as will the cable to the fan. Shower pullswitch is currently surface mount on the bathroom ceiling, but when I do the work I'm going to make it flush.


breezer to do what you propose you would have to run the SAME size cable (that feeds the shower) from the pull cord to your fan (ok so you will have a fuse) but you can not get 2 X 6mm or 2 X 10mm cables into a pull cord,

Why is that? Looking at the sketch I did I wonder if it depends on what goes on inside the control unit/transformer - could there be a path for current to flow to the shower along the permanent live and back along the switched live?

The mechanical problem of cable size could be fixed by using a junction box - assuming I could get the cores into the transformer...

Or I could use a relay to isolate the switching of the supplies to the fan.

Also the fuse holdes you show could not be connected to a 6 or 10mm cable

Yo - I just chose that image to illustrate the type of fuseholder I meant - others are available with larger terminals.

 

[spark]

Breezer is quite right, if you're going to reduce the current carrying capacity of a cable in a circuit, then you must provide a suitable fuse to protect it from fault current. Generally you fuse down before the point at which you reduce the size of your cable, but there is a regulation (but there are restrictions) that permits you to fuse down after the point at which you reduce the size of the cable. I have never done this in a domestic situation and wouldn't recommend it unless you really need to come from the shower. Why do you really not want to come from the lights?

If it was my house and I really needed to supply the fan from the shower I would install as follows:

Mount another flush box immediately next to the shower pullcord.

Take a 3 core+E cable from the shower isolator to the new flush box. Connect the 3 core so that the red is taken from the live supply (input) terminal, the yellow connects to the live load (output) terminal and the neutral connects to the supply neutral terminal.

At the other end, in the new flush box, fit an MK 2-Gang Grid plate (+yolk) part number K3632 and two MK fuse modules part number K4890. Connect your yellow through one fuse module, connect the red through the other fuse module and put the neutral in a connector block.

Then take another 3 core out to your fan isolator from the new flush box and then on to your fan from the isolator.

If your shower pull cord is mounted in zone 1 or 2 you will need to mount the new fuse modules as close as practicable to the shower isolator (to minimise the length of run) but outside zones 1 and 2.

As I said, this is permitted but would not recommend it unless you really need to and you must ensure that the run of 3 core between the shower isolator and the fuse modules is very tidy, very well secured, well out of harms way, absolutelt no more than 3 metres and as short as practicable.

 

[breezer]

to elaborate on why spark said i am right the problem is that if you run say a 1.5 cable from the shower pull cord to the spur (for your fan) in effect you have a 40 amp fuse protecting a 1.5 mm cable if something were to go wrong the 1.5 mm cable would melt before the fuse (or mcb) even thinks of going, and consequently it may cause a Fire insurance company will then not pay out as it was not done properly.

that is why you should run the same size cable from the pull cord to the spur, but that gives the problem two 6 or 10 mm cables will not fit in the same terminal.

Another thought is that with an electric shower must people will turn it off after using it at the shower not the pull cord, so your fan will still be running. By feeding the fan from the lights not only is it safer also people dont leave a bathroom with the lights on, unless you are mrs breezer

 

[Scoby_Beasley]

By feeding the fan from the lights not only is it safer also people dont leave a bathroom with the lights on, unless you are mrs breezer

Mrs Beasley and the juniors are just as bad.It's like a day trip to Blackpool approaching my house, every b***dy light is left on, I'm thinking of removing all switches and hot wiring all the lights in to make it easier when decorating

 

[masona]

My family nickname me 'lighthouse keeper' that all I do is to go round & round to switch the flipping lights out,only cos' I'm the one that paying the bills

 

[Scoby_Beasley]

THIS could be the answer to our dreams masona/breezer, just doesn't give you long enough to finish the Express crossword is my only concern !!

 

[breezer]

you may jest scoby, but i am seriously considering one of these as it is out of harms way, water proof and only works when it is dark

I have also seen similar built into a standard light switch

 

[masona]

Well that the wall lights covered,what about the ring mains!!! Television,CD player & PC all left on when they've gone out !!!


Scoby_Beasley,Time Delay Switch Pneumatic are good but I've seen people put cellotape across them to override it

Breezer,we have a florescence lighting at work with no wall light switch and only come on when you're in the room and I can't see pir anywhere so as you say they must be built into lighting housing somewhere.

 

[breezer]

no i bet not, it will be behind you (they always are, no matter what you are looking for, its behind you)

I have also seen it where the pir is mounted on the cable tray or trunking that the lights are fitted to.

 

[Scoby_Beasley]

Perhaps a DtD pir should be the answer then, when you walk in, on comes the light, when you walk out, off it goes, might save me getting laryngitis

 

[spark]

I'm preparing now for when mine is older. Most of my new house is going to be wired in radials via contactors. The other bedrooms will be via contactors controlled from my bedroom so I won't get any teenage loud music tantrums; one flick of the key-switch and I can isolate the power to that bedroom without affecting anything else