PIR curiosity

[Harry Bloomfield]

PIR, is a two terminal, L and SL, designed as a replacement for a one gang wall switch and installed in my utility room. I installed it several years ago, because often you would walk in or out with both hands full. It has always worked fine, apart from if you spend any time working in there, where it cannot see you, as happened a few weeks ago fixing the washing machine in the far corner. Light would go out, plunging me into darkness, so as a botch, I moved the switch wire, into the L terminal with the live, turning the light out by simply twisting the tube in it's end caps.

The PIR includes a red LED, which flashes red when it is triggered and a NiCad battery. Even when there was no motion to trigger it, I would hear the relay click and see the LED flashing, so basically it would switch off for a few seconds them retrigger. On finishing the washer repairs I refitted the PIR switch, but it continued to misbehave, so I decided to buy a replacement, designed to fit by the light, where it could 'see' anyone in the room - that is no working and much better than the wall switch PIR.

The curious part - Connect the wall switch PIR to a live, at the L terminal - nothing in the SL terminal, and it's LED flashes and the relay clicks away, as before. Disconnect it from any wiring - the LED stops flashing and relay clicking.