I have seen it done and it worked.
Both are wired in parallel .
Ideally though they SHOULD be on the same supply switch or fuse, OTHERWISE you would need to isolate both together to make the system safe, as when one operates, the load side of the pir will feed back to the other side of the pir.
With seperate supplys if you was working on the one isolated pir, if the other was activated the load would come on but then feed back and liven you up.
Personally as a safer way, I would wire the load via two small contactors in an enclosure, wired in parallel switching the load.
Use each pir to control each contactor seperate
Still use the same switch /fuse /spur for the whole set up, but it will be safer as there will be be no direct connection between each pir.
You will need though , pir's that are not affected by a Minimum load to do this.
An even better way
With a similar set up as above you could make the control circuit using 24volt transformer, using discreet small outdoor alarm sensors and smaller 24 volt relays switching the main 240 v light load.
Sorry did not explain very well. Some PIR's use electronic switching these are not suitable to be run in parallel. Unless like rocky says you use relay. But as long as the type used has a relay built into it the switched outputs from both PIR's can be connected together. As long as both feed from same source. So I would expect 3 core and earth between PIR's connecting Live, Neutral, and Switch of both PIR's together. Two core and earth feeding one of PIR's and two core and earth feeding lamp or lamps. Because you may need to use SWA you may need junction boxes to terminate glands. This will most likely come under Part P if your not in Scotland and even if not it would be prudent to get it tested. I had though you were only asking if it could be done I had not expected you to be doing the job. I would recommend using an electrician you may find one who will allow you to do laboring jobs so reducing price.
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