Dual input switched live

[i_am_fubar]

I'm going to have the extractor fan tied into the lights via a switch live so that the fan comes on when the lights do, and stays on for x amount of time after. Light switch outside the bathroom along with isolator.

I will also have some controls for towel rail, mirror heater, mirror lights... etc located inside the bathroom near the basin.

It would be easy to fit a momentary switch there too, so I can tap the fan on for x amount of time only. Just parallel up the switched live from the lights to the momentary switch. However, this would cause the lights to come on while the switch is pressed.

Unlike good ol' DC, I can't stick a diode in there to stop this. Are there any other options to allow a secondary 'fan on' switch, without inadvertently also switching on the lights?

(also, need it to not swtich the lights off if they are already on)

Cheers,
Fubar.

 

[EFLImpudence]

Double pole switch.

 

[AndyPRK]

U mean a 2 way switch with com connected to the fan
L1 live
L2 light

 

[EFLImpudence]

No, that would be no good.

Double pole - to separate the light and fan supplies when OFF so that it does not back feed to the light when second fan switch on.

 

[AndyPRK]

How would yours be wired then?

 

[Lectrician]

Yep, double pole light switch outside door.

 

[EFLImpudence]

How would yours be wired then?

Supply to both 'ins'

One 'out' to light and the other to fan.

 

[SimonH2]

No, that would be no good.

It would work fine - tap the switch, com connects to L1 (live - should be the same as the light circuit) and fan comes on, release the switch and it reverts to L2 (switched live so works with the light as normal).
However, the challenge may be to find a momentary switch that's also changeover - not having bought one I don't know whether they tend to be single throw or double throw switching.

 

[EFLImpudence]

No, that would be no good.

It would work fine - tap the switch, com connects to L1 (live - should be the same as the light circuit) and fan comes on, release the switch and it reverts to L2 (switched live so works with the light as normal).

But it has to work the light as well, as normal usage.

 

[SimonH2]

I think you misunderstood, the two-way switch is to trigger the fan. The light still has it's normal switch.

So normal light switch operating the light. Then three way isolator for the fan.
From the isolator, the L&N got to the fan, a L&SL go to the momentary switch, and the COM on the momentary switch goes to the fan SL.

With the momentary switch in it's rest position, the fan SL connects to the light SL as normal and operates with the light. A tap on the switch momentary connects the fan SL to L regardless of the light switch position.

 

[AndyPRK]

I have seen 2 way momentary switches although they have a bell symbol.

With the fans I have seen It would need a long press of the switch.

 

[EFLImpudence]

Ah, right. Sorry.

Was only thinking of the main switch.

 

[i_am_fubar]

Thanks for the replies guys. Some good ideas, and with a chat I had with a mate last night, I think I've got it sussed.

Untitled

• i_am_fubar
• 7 Jan 2014
• 1

There are some additional isolators I want to put in to isolate all power to the sink area and some additional fuses. But as a general scheme, this should work where the light switch acts as a master control for the lights (by controlling the neutral return path). And the aux fan switch can operate without interfering with the lights.

Cheers, Fubar.

 

[AndyPRK]

It would work.

It's would be quite a lot of unrequired effort to bring a new neutral and return neutral to the light switch. (unless its already wired with that method)


I do question the whole requirement though, if you have a switch to trigger the fan timer, you may as well just have a latching wall switch to trigger the fan&timer, as there are times when you want the light on but not the fan (e.g at night)

 

[bernardgreen]

One option would be to use a momentary push button change over switch to switch the switched live to the fan.

Normally this switch would connect the fan's switched live to the lamp's switched live.

Pressing the switch would disconnect the fan's switched live from the lamp's switched live and connect it instead to permanent live.


Switch common to fan's switched live

Switch L1 to permanent live

Switch L2 to lamp's switched live.

( Maybe L1 and L2 might need to be the other way round, I don't know which way push button change over switches work on L1 and L2 )