Electrics

[bodgerfederer]

Shower extractor fan and light problem. I have wired it up like this (ignoring earths for simplicity). I'll start at the junction box. There are three terminals here: Live, Switched Live and Neutral.

Three wires are attached to the Live terminal: the first from the feed, the second to the light and fan switch (located outside the shower room) and the third to the fan isolator (and then on to the timer fan).

Three wires are also attached to the Switched Live terminal: the first comes from the light and fan switch, the second goes to the fan isolator (and then on to the fan) and the third goes to the shower light (via a 240V to 12V transformer).

Three wires are also attached to the Neutral terminal: the first comes from the feed, the second goes to the fan isolator (and then on to the fan) and the third goes to the fan light (via the transformer).

Here is the problem:If the fan isolator switch is on and I turn the fan and light switch on, the fan hums, but hardly moves round at all, and the light is very dim. I measured the voltage going to both the fan and the transformer (for the light) and it came in each case to about 50V (not 240V) which means perhaps (I am not an electrician) that they are in series? If I remove the light altogether, the fan works fine. If I remove the fan, the light works fine. What am I doing wrong?

 

[breezer]

use the edit button to put some spaces in it will you

 

[ColJack]

you may have the wires to the transformer in the wrong holes.. putting the transformer in series with the light / fan switch..

you may have the switched live and neutral backwards or crossed somewhere on the way to ( or at ) the fan..

it's best to disconnect all of the wires, bell them out and make certain to lable them.. then connect as per the diagram I will post in a bit.. ( takes time to draw.. )

 

[bodgerfederer]

Thank you ColJack for your reply and drawing. That is exactly as I wired it. I'll check tomorrow morning that I don't have any crossed wires and that I wired up the transformer correctly.

 

[bodgerfederer]

Right: I've checked all my wires and it's all exactly as drawn by ColJack above. I've tried the transformer both ways and the whole system fails in just the same way whichever way it is wired up.

I flick the switch and this is what happens: the light flares up properly for about 5 or 10 seconds, and then dims to a faint glow; the fan hums but never properly gets going. When I flick the switch off, the light goes off (as it should) and the fan gets going properly and carries on going until the overrun time is up (as it should). The fan is working at this time not from the switched live but from the permanent live (which is clearly a good connection).

I thought to myself then: it must be a fault with the fan, so I took away the fan (and the fan isolator) and just put a light there instead.

When I flicked the switch on this time, both lights were dim again.

Then I thought: it must be a fault with the fan light. So I took away the fan light and replaced it with another light.

Same result again: the fan never got going and the light was dim.

The wiring seems right, the fan seems right, the light seems right---but when I put them all together.... I'm going mad.

 

[bodgerfederer]

Another clue: When the whole fan and light system is switched off the voltage across the live and neutral feed is 240; when it is switched on, the voltage throughout the circuit (before it gets to the transformer) is 50, that is, across the feed (L & N) and across all other points in the circuit, L & N and S/L & N.

Anybody any ideas?

 

[bodgerfederer]

What about this? In order to get my power I just cut into a random lighting circuit cable in my loft. Could I have chosen the wrong one? Is it a problem with the feed?

 

[bernardgreen]

What about this? In order to get my power I just cut into a random lighting circuit cable in my loft. Could I have chosen the wrong one? Is it a problem with the feed?

Never work on random cables... check twice before cutting.

You have probably cut into a cable froma ceiling rose ( lamp A ) to the switch for that lamp. The red will be live, the black the switched live back from the switch to feed the lamp A.

This means the fan wil be in series with lamp A. Lamp A will come on dimly when you turn the fan ON as long as the switch for bulb A is OFF.

The fan may or may not run as it is not getting full voltage.

Turn the switch for bulb A ON and the fan will stop and bulb A will light normally.

 

[bodgerfederer]

Hallelujah!

 

[bodgerfederer]

Thank you Bernard Green. That was it. I picked another random cable (!)and this time it worked.

 

[bernardgreen]

Glad you fixed it but please

do NOT work by random selection......

And repair the switch wire with a proper junction box that is accessible

 

[bodgerfederer]

No I won't.

And yes I will.

Thanks again.