Grant(e) said:
I know what you are all thinking... NOT another post on this subject.
I have read the previous posts on the subject and can someone please post a wiring diagram for (a) wiring to a light circuit and (b) wiring from a shower Isolator switch.
I'll come to (b) in a minute, but regarding (a), if you know how lighting circuits work, and what supplies timed overrun fans need, it should be self evident. If you don't know these things, maybe you should study them before getting too heavily involved in wiring. Have you looked at the diagrams of lighting circuits in the For Reference section? Bought the Which? book?
I have already installed one of my fans to the light circuit but I could not see any other way round it and ended up fusing the live feed to both the light and the fan via a 3amp fuse.
That's the most obvious solution - something like this
and it works fine - the combined load of light and fan is OK for a 3A fuse. The only drawback is that if the fuse blows you lose the light.
An alternative method is to use a DP light switch, then the fan supply can be separate to the lighting one, and therefore the light is not on the same fuse:
the added bonus of this method is that if you use a switched FCU you no longer need a fan isolation switch.
I want the other fan to come on when the shower isolator is turned on, which in its self is straight forward, but where does the live come from for the run on?
I want that too, and it is
not straightforward because of the problems of cable sizes and fusing down.
To switch the fan as you want means that you have to supply it via the shower pull switch, and as you should really use 10mm² cable from the switch to the FCU (or whatever size cable your shower circuit is - even if it is currently 6mm² you should plan for 10mm², as you might have that in the future). After the FCU 1mm² will be enough.
The problem is that you can't get 2 x 10mm² cables into the terminals of the switch, so you need some sort of junction box. I've seen the photo of the 60A jobbie that TLC sell, and it doesn't look as though it will take two cables into one side, but it is worth checking with TLC. The other option would be to use a Henley block - that will certainly have the capacity, but then you've got the problem of how to prepare the cable ends, as you shouldn't remove the sheath outside of the block, but it's not designed to take sheathed T/E inside it....
If you have a timed overrun fan, the position is further complicated by the fact that you need to sort out two feeds, permanent and switched live, so simply using the shower supply would need two JBs/Henlys, and two FCUs, and it all starts to get a bit messy.
What I plan to do is to have a small box with a DIN rail in it, into which I bring the switched shower supply. On the rail I will have some through terminals with bus-bar interconnections to give me two sets of outgoing 10mm², one for the shower, the other going to the coil of a rail mounted contactor. Also entering the box and first going through a rail mounted fuse carrier will be a 1mm² cable from the lighting circuit (yes, I will label the box accordingly). From the fuse I'll take the permanent live for the fan, and a connection to the contactor terminals to give me the switched live. But this is probably not a solution that many people would want to implement....
I have drawn a diagram of what I have already done but I cannot paste it on here
how do you paste diagrams ?
You have to turn the drawing into an image file, by scanning if it's on paper, or exporting as an image from whatever drawing tool you used, and then either upload the image to your webspace, if you have any, or upload it to a free image hosting site.
See
//www.diynot.com/forums/viewtopic.php?p=86738#86738 for details I posted earlier on.
I'd be interested to see your plan, I'm worried that if you think it's straightforward you might have missed something...
