Two PIR sensors to actuate one device

You can parallel as many pirs as you like provided they are of the relay type which most are. The toolstation ones I bought had relays.

The ones with solid state switches will also work if you can wire a manual override switch to them as they can take mains on the output as provided by the manual override switch.

Virtually all have relays in now as it removes any issues with triacs not liking certain types of load.

Cheers. Terry.

Are the PIRs powered by a common source?

ie are they fed from the same circuit

No, one is fed from his house, the other from a battery, and the other from the streetlights circuit he hotwired into. WTF?

That is different "supply" not "circuit".

A different circuit wouldn't matter. Same voltage, same phase, etc.

But you know exactly why they should not be off different circuits.

I cannot think of a reason. The only thing I can think of that you may be getting at is it would bypass a blown breaker if both sensors switched on at once. But then the other breaker would just break on the same fault.

A different circuit *would* matter. Think about it.

With most PIRs and have no problem.

Make sure they are all fed form the same circuit though.

Only if they have the latest protection. I assumed they would be on the same circuit but you are probably correct in saying so.

Hi. Thanks for all the replies. Yes, the PIRs will be fed from the same circuit. The plan is to wire a phot osensor trigger, whose output goes live in darkness, to a relay, such that I get a "on" switch in daylight only. The two PIRs will both be supplied by the same output of that relay so that they are active in daylight only (wh ich is what I need). Both PIR outputs will be connected to the same power t erminals of the single device that I intend to have them control, which, in turn, ought to keep herons away from my pond! Lol.

Cheers. Terry.

The toolstation PIRs have built in photocells. They only operate in the dark once you set the brightness knob to low.

I have, and there is no reason. The voltage and phase from it is identical.

Try again, voltage or phase are not the issues.

I won't try again, because there is no other reason.

Dennis and John have both given different reasons.

Both are viable reasons.

Nobody gave any reason, all I've seen is "It would matter".

Ah - the moron's defence...