PIR occupancy switch problem?

[ste mac]

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?

 

[malcolmsanford]

Off the top of my head ............. perhaps a diode in the circuit

 

[spark 68]

Hmm,

That is probably the reason for the DP light switches originally used, so as to break the N for the light not being used.

I have never seen DP Pir switches, but that is not to say you cannot obtain them.

 

[spark 68]

perhaps a diode in the circuit

I had thought of this Malcom, but it depends if the relays would trigger off halfwave rectified mains @ reduced voltage or not, but this still leaves the problems of the N connected, where as it was originally broken by the DP switch.

Edit; oops! meant to say the lamps would be running off HW rectified mains as well, and may flicker badly

 

[spark 68]

It would be possible to do with two DP relays, each switched by it's own Pir switch, this would then fully isolate the unused light.

 

[chronyx]

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.

Sorry to hijack the thead but I'm struggling to picture this in my mind and want to understand the reason behind this happening in case I ever have a similar problem!

How would a double pole PIR/relay help?

Thanks for any info!

 

[spark 68]

Hi Chronyx,

I was having a bit of a Blonde moment earlier on, any way I drew the circuits out, sorry for the scrappy drawing as Iam just finding my way around the drawing package.

I suspect this is wired as per my drawing named 'original' which had DP switches, if it was done like this ?, it is not good practice, as you will have a switched live at the lamp which is off.

The second drawing with PIRs, these are single pole and so giving the symptoms the OP was complaining about!, as the switched lives are backfeeding on to the unused lamp, as it was in the first drawing, but with the neutral disconnected via the DP switch, this would not have been noticed, as the lamp was off.

I have added a third drawing, showing diodes (as Malcom mentioned) to stop the backfeed, but it is debatable if this would work in practice.

I have not completed the drawing with the DP relays yet, but it would basically be just slaved off each PIR, to give DP switching as in the original drawing.

 

[needasparks]

Why have the fans been left with the timers connected, surely the pir is now doing the timer part so the fans just need L/SL inked out so are just fed via the pir. Makes no sence having a timer feeding a timer.

 

[spark 68]

I have no idea needasparks,

but that still would not solve the op's problem, which is one fan shared between two lamps, they would still back feed each other.

 

[needasparks]

Yeah i see now, just read again.
It cant safely be separated for maintenace purposes with things like diodes so i would not even go down that route.
as for as i can see you have two options, either link pirs properly so both toilets come on together or install another fan.
As its a village hall i would think both toilets are used about the same when open anyway and the lights would only be on for a few minutes so the cost to install another fan would far outweigh the odd two minute light on when someones not in the other loo.

 

[spark 68]

I agree needasparks,

It cant safely be separated for maintenace purposes

I suspect this is wired as per my drawing named 'original' which had DP switches, if it was done like this ?, it is not good practice, as you will have a switched live at the lamp which is off.

 

[needasparks]

Yes, I speed read first so missed the one fan bit. correct matey, this is a village hall so would think any numty over the years will be changing lamps extra so really not good to have this kind of setup. It can be labeled to death but still would not be understood so would be easier to keep it simple.
Public buildings need a simple system or all sorts of things will come back and haunt ya if its changed from the normal. Most of these places run on a small budget so cost will always come before anything else.

 

[ste mac]

I should have been a bit clearer about the 2 pole switches. 1 pole is used to switch the lights & the other pole is used to trigger the fan. The live feed to the switch was linked across the two poles. Because the PIR switch only has 1 output I have put the fan and lights output together and hence I now have the backfeed problem.

 

[spark 68]

Ah! I see,

lol I said I was having a blonde moment!

I will try and draw it out again, and see what I can come up with (to make amends).

 

[spark 68]

Is this how it was wired originally ?