Fluorescent bathroom lights from main room spur

[Loofah]

Hi,

Had a look around the forums and Wiki but can't seem to find an answer to this...

I've moved house and the bathroom has a dimmer controlling several halogen downlighters. There is also a mirror with fluorescent lights in it and its own light switch. When the main lights are on you can't operate the lighted mirror as the fluoro tubes flicker very dimly; if the main lights are off then the illuminated mirror operates ok. I checked out the wiring in the loft and the mirror power has been taken from the same spur as the one that powers the dimmable halogens, presumably this is what is causing the problem with the dimmer affecting the fluorescent tubes.

My question is - can I isolate the fluorescent tubes in the mirror from the effects of the dimmer switch? If so, how?

I also want to put in an extractor fan in place of one of the lights directly above the shower unit but from what I've read in the threads I'd need a separate circuit?

 

[bernardgreen]

Looks like the mirror lights have been wired from the red and black wire in the switch. The person who connected it must have assumed red was live and black was neutral.

Needs to be re-wired to the live (loop) and neutral from the CU

 

[Loofah]

Not to sound like an idiot, but what's a 'CU'?

And thanks for the reply - much appreciated.

 

[Loofah]

DOH! Consumer unit!

 

[Space cat]

Looks like the mirror lights have been wired from the red and black wire in the switch.

That idea doesn't fit the symptoms as described. If the mirror lights were connected across the ceiling light switch then (a) both sets of lights would try to work (badly) all the time and (b) the mirror lights wouldn't work at all if the ceiling lights were on.

The only plausible answer I can come up with off the top of my head is that there is something else in series with both - but what? Let's hope it's not a bad connection because it'll be getting pretty hot!

 

[bernardgreen]

(b) the mirror lights wouldn't work at all if the ceiling lights were on

For the time in each cycle the dimmer triac is OFF the flourescents will have some voltage..

As to the two being in series and sharing the supply volts the flourescents may be very high impedance if the starter doesn't conduct on the available voltage so no current path.

It is a pair of complex networks in series. Anything could happen.

 

[Space cat]

For the time in each cycle the dimmer triac is OFF the flourescents will have some voltage.

Quite right. I read the post in a hurry and forgot about the dimmer. Loofah, do the mirror lights change when you adjust the ceiling lights. Do they go out when you turn the ceiling light up to full brightness?

 

[Loofah]

Looks like bernard was right first off, wire wasn't going to neutral. All fixed
Cheers for the input though Space Cat, it's good to know people on the forum all want to help out.

Second part of my original post was regarding an extractor fan... I can't have this attached to the dimmer switch circuit so am I left with just the option of installing a separate switch or is there a way round that? I want the fan to come on with the lights ideally...

 

[Space cat]

What terminals do you have on the back of your dimmer switch? If there are only two you're out of luck. With three it might be possible and with four I'd say it should be possible. What you need is a terminal that gives access to a point between the dimmer part of the switch and the on-off part. I've got one here that combines a two-way switch with a dimmer. One side of the dimmer is connected internally to COM but I have access to all three terminals of the two-way switch. The trick is to bring the live feed to the switch part first then connect the fan to the middle terminal (COM in my case). The lights go at the far end after the dimmer.

 

[Loofah]

On the back I have L1, L2 and the wavy line with an arrow through it (dimmer). Oh and earth of course...

So you're saying that I could install the fan if I break into the wire at the right points / terminals? That would be great!

 

[Space cat]

With the three terminals you've got it MIGHT be possible. The wavy lined terminal is one side of the dimmer. This is where the wire to your lights needs to be. Live feed will go in one of the others. If it doesn't make any difference which one you use, the switch is a two way and you have no access to the COM terminal. You're out of luck. If one of them works correctly but the other one disables the switch and leaves you with only the dimmer, you're there. Put the live feed in the one that makes it all work correctly and the fan in the other one. This should give you what you want.

 

[Loofah]

Checked - it's a two way Could I replace the switch with an alternate dimmer, if so what would you suggest?

 

[Space cat]

Sorry Loofah, I don't know of a particular make and model that will do. I've got one here but it's over twenty years old (bought from Woolworths) so that doesn't help. You need one that gives you direct access to both sides of the dimmer and also to both sides of the switch.

Such a device must have at least three terminals: switch in, common and dimmer out. Or it might be like mine which has the three terminals of a two way switch and the dimmer between COM and a fourth terminal. Or it could have a dimmer and a switch in the same box but isolated from each other. You'll just have to hunt around - unless somebody else around here knows the answer.

 

[Loofah]

hehehe, wish me luck, I may be some time....

Thank for all your help