Wiring PIR in parallel with standard switch?

amcluesent

So in my glass-windowed porch, I have four 240V (no transformer) halogen ceiling lights, wired to a standard wall-switch.

I'd like an external PIR which will detect approach and switch on the existing lights for a set period, as the light going through the glass provides plenty of illumination.

What prevents me wiring up the PIR and light-switch in parallel, so either can energise the light set?

Is it doable, is it Part P legal?

TimBuckTeeth

It depends on how the PIR switches the lamp, if it uses a relay on the circuit board then it would be possible, but if it switches electronically (using a triac - should be labeled not suitable for fluorescent lamps) then the PIR may be damaged .

Either way it is not really a good way of connecting it. A two way or changeover switch should be used : the lamp should be connected to the COM terminal on the switch, L2 to the switched live output from the PIR and L1 to the Live supply. With the PIR live feed permanently connected. You might need a new switch (2 way) if the L2 terminal is missing on the existing switch.