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Extractor fan relay for two independent light switches

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metanet

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Thinking a 240V AC relay activated by two independent light switches could be used to switch power to a shared inline extractor fan. The fan serves two bathrooms, just needs to be activated from two different switched live lighting circuits.
I'm aware double pole light switches could be used in this scenario but the light switches didn't pass wife test.

Anyone know of a dual input relay I could use for this purpose?

Thanks
Meta
 
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Simon47 said:
Sorry, no diagram, but here goes.
Relay coil to one light S/L, relay pulls in when that light is on.
Contact (needs to be C/O) common to fan S/L input.
Connect contact N/O to same S/L as coil.
Connect N/C contact to S/L on other light.

Switching one light on pulls in the relay, changes over the contacts, and applies live to fan control. Fan runs.
With that light off, tge fan is controlled by the other light as if the relay wasn't there.

The above assumes bith lights on same circuit. If on different circuits, relay coil S/L & N come from one circuit. The N/O contact must connect to the permanent L the fan is connected to - needs an extra cable core.
Click to expand...
[ElectriciansForums.net] Extractor fan relay for two independent light switches
 
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suffolkspark said:
Id just get another inline fan probably as cheap as relays and enclosures
Click to expand...
You can fit a relay in a backbox - and you'll most likely have one already for an isolation/maintenance switch. And it'll cost (if you pick sensibly) less than some of the switches people have been suggesting, and definitely less than an extra fan.
 
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Like Simon47, Post #14 I was assuming all to be on same RCD protected circuit and maybe just a L & S/L at the switch! in an existing installation with loft access. Maybe it is being wired from scratch so is open to other options, but just re-read OP's post ........
metanet said:
from two different switched live lighting circuits.
Click to expand...
TWO different circuits requires a different solution!
 
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DefyG said:
TWO different circuits requires a different solution!
Click to expand...
The OP only says it's two different S/L circuits - I would read that as two different S/Ls, but probably still on the same MCB.
If it is split across two different circuits, that's easy to handle - as I mentioned above, you just take the N/O contact of the relay to the permanent live of the circuit the fan is on. So the relay simple switches the fan between the switched live for that circuit, and to the permanent live for the same circuit when the light on the other circuit is turned on. The relay coil is connected to the lighting circuit that the fan isn't on - and it takes care of the isolation.
 
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metanet said:
Thinking a 240V AC relay activated by two independent light switches could be used to switch power to a shared inline extractor fan. The fan serves two bathrooms, just needs to be activated from two different switched live lighting circuits.
I'm aware double pole light switches could be used in this scenario but the light switches didn't pass wife test.

Anyone know of a dual input relay I could use for this purpose?

Thanks
Meta
Click to expand...
When you say double pole, did you mean, double pole in each switch for the bulb a jumper from each live to the fan and fan permanent neutral. With no relays ?.
 
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Simon47 said:
Oh yes, the relay will hum when on. It's possible to add a couple of diodes so the coil operates on DC, and it's inductance will smooth out the half wave and eliminate the hum.
Click to expand...
It's not a good idea to drive an AC relay coil with DC.
 
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Simon47 said:
The OP only says it's two different S/L circuits - I would read that as two different S/Ls,
Click to expand...
You are probably correct as OP doesn't make it clear how its installed, that was my original thinking in my post #6 which incidentally a circuit I had used before and didn't experience any humming (or perhaps drowned out by sound of fan)
😄
 
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richardbatty said:
When you say double pole, did you mean, double pole in each switch for the bulb a jumper from each live to the fan and fan permanent neutral. With no relays ?.
Click to expand...
That's it. But both lights must be on the same circuit.
mainline said:
It's not a good idea to drive an AC relay coil with DC.
Click to expand...
It's quite common - some applications use a purpose designed DC coil, some use an AC coil and just feed it DC. Heatmiser do the latter in their UFH control/wiring centers.
Since it's only half wave, and relies on the coil inductance to maintain the current for over half of each cycle (so it's not smooth DC, and significantly less effective voltage than full-wave & smoothed), I doubt it's particularly bad for the coil.
 
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