PIR occupancy switch problem?

ste mac · Feb 28, 2012

Can anyone offer a solution to this problem:

Male toilets & female toilets in a village hall both have thier own light switches, but are feed from the same MCB.
Both toilets share an extract fan with overrun timer.
I have replaced the 2 pole light switches with PIR switches but now when either PIR is activated both male and female toilet lights come on due to power from one PIR backfeeding the other PIR output via the commoned fan timer trigger wire.

Does anyone know of anyway to prevent the back feed but still operate the fan from either PIR or do I just leave it as is?

The only way I can see is to have 1 fan for each toilet.

Does anyone know of another method that doesn't require rewiring of the circuits?

spark 68 · Feb 28, 2012

This is how it could be wired with your single pole Pir switch, using two DP N/O relays, this would stop you backfeeding to the light that is not in use.

Ps. If I have made any mistakes please be kind enough to point them out, as Iam not used to this drawing package yet.

ste mac · Feb 28, 2012

Spark 68 you are correct with your drawing of the circuit as was.
I think relays or separate fans are the only way forward, unless the customer is ok with the set up as it is.
The original reason for the PIR's was safety of people using the facilities not for energy saving so the current setup maybe acceptable.

Rockingit · Feb 28, 2012

Just use the S/L on the PIR's to activate a contactor to switch the fan timer S/L circuit. One contactor per PIR.

spark 68 · Feb 28, 2012

Thanks for that Ste,

It gave me something to play with on this drawing package (tiny CAD), which Iam trying to get to grips with for something else.

Iam more used to back of smoke packet drawings lol, but I need to get up to speed with the computer, as you can tell, drawing is not my forte.