one light, 2 supplies

I have recently installed an outside light which is switched usind a pir, however I want to install a second pir at the other end of my garden to also swith tyhe same light on when movement is detected. the second pir has a power supply right next to it so I was wondering can I use the 2 suplies, 2 pirs and one light safely, my main concern is that whe pir 1 is on then if pir 2 switches will the two seperate supplies conflict with each other? any advice is greatly appreiciated. Thanks

The two pir relay output contacts would be wired to a common point - thus, if both pirs are triggered, the two supplies would be commoned via the contacts. Not a good idea as, effectively, the two circuit breakers at the distribution board would also be put in parallel. Pirs usually have a small fuse in them but I have come across some that don't.

So this would almost certainly be banned by your wiring regs.

You have to run a cable between the pirs, to link them. So I can't see why it would be a problem to also run power up the link cable. 4 core cable is widely available here, I expect that it is in Australia, too.

In the US it would be a code violation to do that unless both sources were controlled by the same breaker or fuse. In general it is bad practice. You have to run wire from the lights location to that of the new PIR so run three conductor cable and use the third conductor as the controlled switch return for the light.

First, both PIRs must be connected to the same branch circuit. Second, I don't know how well the ones with solid state switches will put up with being wired in parallel. You are better off buying the kind that has a relay. Usually, these are 'heavy duty' and are rated for inductive loads.

There are X10 systems, where the PIR units send out 'on' and 'off' commands via the X10 power line carrier. An X10 receiver (or a bunch of them) can be controlled by them. They need not be on the same circuit, but fed from a common secondary system (you can even turn your neighbor's X10 stuff on and off if you can figure out the channel numbers). I have some of these at my house and they work quite nicely.