Any idea what's going on here?

[SUNRAY]

Light dimmer switch on - 1 - 0V / 2 - 266V / 3 - 0V

Light dimmer off - 1 - 0V / 2 - 266V / 3 - 0V

Fan switch off - zero readings on any cable

Fan switch on - 266V on cable 2 only

The voltage from cable 2 flys around upto 700, then stabilises once good connection to multimeter.

Also, my mistake. The flat twin which I said had only 2 wires, actually has 2 brown and a bare wire.

Thanks again guys, very much appreciated.

Thanks, excellent work. This will make the fan work but without the run-on timer facility.

If you would you like the timer function to work there is some more testing for you to do,

With the power off at the consumer unit [fuse box], using the Ω setting of your multimeter [or the buzzer setting] test between this number 4 wire and number 3. is it very near 0Ω or the buzzer sounds?

 

[hellboy]

2 looks like a permanent live that comes from the switched side (if you see what I mean) of the fan iso.

With the fan switch on and the light on, you should get a live that goes off when the light does.

Just checked and double checked....there is now 286V at No 2 cable, regardless of the light dimmer switch position

 

[hellboy]

Thanks, excellent work. This will make the fan work but without the run-on timer facility.
View attachment 198112
If you would you like the timer function to work there is some more testing for you to do,

With the power off at the consumer unit [fuse box], using the Ω setting of your multimeter [or the buzzer setting] test between this number 4 wire and number 3. is it very near 0Ω or the buzzer sounds?
View attachment 198113

The 3/4 wires are about 3m apart, so unable to do the above?

Also, there are zero readings from the cable that has the neutral into the junction box. All electrics and lights are working, could it be this was intended for something else? Where is that neutral likely to goto?

Another question. As the position of the light dimmer has no bearing on the voltage at wire 2, is it possible the dimmer has been wired incorrectly, causing the feed to the extractor fan switch to be permanently live??

Thanks again, amazing help.

 

[securespark]

Just checked and double checked....there is now 286V at No 2 cable, regardless of the light dimmer switch position

I'm sorry if I confused you. When I said that there should be a live that comes on when the light is turned on, I meant in addition to the number 2 conductor.

 

[ajohn]

I’ve dumped the screwdriver!

It's way better than nothing but always test it's working on something that you know is live.

 

[SUNRAY]

Just checked and double checked....there is now 286V at No 2 cable, regardless of the light dimmer switch position

Thanks for the update, that is what I understood from reply #13

I'm sorry if I confused you. When I said that there should be a live that comes on when the light is turned on, I meant in addition to the number 2 conductor.

SS,
I think this is the current set-up, independant of the light:

and the fan is not currently started by the light switch, just the fan switch.
The actual arrangement for the light fitting is not important, it could be a rose, junction box or a 4th terminal in a spotlight etc.

Hellboy,
I think the person who wire this originally only had twin and earth cable so wire number '1' has always been surplous and the same is probably true for nmber '3' which I think is the other end of number '4'. If this is the case the original fan was either a 'non timer' unit or wired to operate in that mode.
The neutral has [I think] been connected to any random neutral point hopefully on the lighting circuit and very probably at the bathroom light fitting. Can the cables be traced in the loft?

If you want it to be operated by an independant switch and don't require the timer function [as current] then simply wire as shown in post #16 with number '2' and neutral.
If you want to use the timer function then more testing of cables is required. Potentialy we can also get it operated by the light switch.

The question at the moment is how do you want the new fan to operate?

 

[securespark]

Cheers, SR.

Misunderstood that.

 

[SUNRAY]

Cheers, SR.

Misunderstood that.

As I wrote 'I think' that's it.

 

[securespark]

From looking the whole thread over again, "I think" you're right!

 

[hellboy]

View attachment 198155
The neutral has [I think] been connected to any random neutral point hopefully on the lighting circuit and very probably at the bathroom light fitting. Can the cables be traced in the loft? - It's a victorian terrace, its a closed roof space above.

If you want to use the timer function then more testing of cables is required. Potentialy we can also get it operated by the light switch. - All ears!

The question at the moment is how do you want the new fan to operate?[/QUOTE]

Awesome, that diagram makes sense to even me!

Well, preferably we'd like the light to run on a timer, but I imagine its going to need more wiring? The current cables are chased into the walls and there's no chance we'd be wanting to rip walls apart!

 

[SUNRAY]

Well, preferably we'd like the light to run on a timer, but I imagine its going to need more wiring? The current cables are chased into the walls and there's no chance we'd be wanting to rip walls apart!

In that case I'll go back to #16 and you will have to find a way of extending the leads on your multimeter to see IF wire 3 and 4 are one and the same. with the power turned off and using the Ω range.

To put you in the picture, this is what we are attempting to achieve but not until you have verified that wire:
Drawing removed as it contained an error.
And we also need to decide what to do with the existing fan switch.

 

[SUNRAY]

Revised drawing to correct error

 

[hellboy]

Hi fellas,

Apologies for the delayed update, I got sidetracked with a couple of other jobs in the house. So, I've wired as per post 16 and all appears to be working fine. I opted against wiring for the timer as the current set up suits us just fine.

Just to say a big thanks to all of you who helped me out, especially SUNRAY. You fellas do a great thing, parting with your knowledge to strangers, for nothing.

Thanks