2 way PIR switch

I don't think you want a "2 way PIR". (I'm not sure what that would mean. If PR1 has turned the lights on then if PIR2 is also triggered it turns them off?) Being pedantic, I think you want the lights on if either PIR1 or PIR2 *or both* are triggered :)

You can do that by wiring two PIRs in parallel from the same supply. But check the PIRs are OK being wired in parallel. It's a while since I did this and at that time some weren't at all happy with a live "coming back at them" (as it were).

Belatedly realised this is probably covered in the Wiki, and lo, complete with picture, from John Rumm :

just connect the PIR outputs together, this has nothing to do with 2 way switching.

NT

Would something in the circuit prevent a problem?

Relays could. I'd try them connected first.

I doubt you'd want a two way PIR where one coming on would switch off the other?

You need to parallel connect them. So either coming on brings on the lights.

Relays

You don't actually need a two way switch. You want the lights coming on if either or both detectors are activated. You need to link the PIR switches in parallel.

(The "off" function is automatic.)

I connected mine like this a year or so back. Got some single core cable from an eBay seller to make the connection. It works a treat.

Not usually required... (and many PIRs will have a relay on the output anyway)

I have used several different types[1] without any difficulty. Including some built into lamp fittings to switch both internal and external lamps.

Thanks to all for your comments and explanations. I saw the Wiki but misunderstood the diagram. I thought it was similar to 2 way wiring at the top/bottom of a staircase for example. I now understand thanks to you guys. I like the look of the TLC ones mentioned by John but Robin comments that I should check if they are suitable for wiring in parallel. How do I do this?

Pete

You may be able to download the manuals - but they may not mention it either way. Chances are they will work just fine. (I have not found any that did not)

If you look at the instructions for the TLC one I posted a link to:

Here is another:

I agree (of course) but just to check that my memory wasn't /that/ far gone I've dug back and found the ones I had to return (because I didn't RTFM before buying) because the instns said they couldn't be wired in parallel. Turns out they were 2-wire Clipsal 750WP. And it was even longer ago than I'd thought.

Thanks both. That's the next project sorted while I'm confined to barracks. Stay safe and keep well. Pete

Yup 2 wire is a different beast - with no neutral reference, it needs to bleed a small current through the load even when "off" to allow it to self power. If you make the output live externally, then it now has two live connections and no neutral - in effect turning the non active device completely off.

That may in practice still work after a fashion[1] - each being able to turn the lights on - but you would lose that "wired OR" functionality that would allow both devices to be triggered, and the lights only go off when the last PIR reaches the end of its preset "on" time.

I don't know if this always applies: when deciding on a PIR I've looked for it being OK with CFL, on the assumption that it has a relay.

Yup, that's usually a safe bet. While being CFL compatible does not guarantee it has a relay as such (i.e. it could use a triac output stage to switch the load) - it indicates that it does not draw its own power through the load, which is the potential show stopper here (pun possibly intended!)

Just to finish off this topic, I've installed the lights and sensors and they're working fine. Really pleased with the result. I used the Pir's suggested by John from TLC and some LED downlights from them also. Ordered them last Monday at 1.00pm 'ish and they were delivered The following day at 10.30am 'ish, on their standard delivery service. Excellent service from TLC and DHL in these difficult times. Thanks again to all. Pete