'Backfeeding' a PIR

[PeterC]

Having put a PIR on an outside light, it would be convenient to be able to switch it on manually. The usual switching pattern doesn't keep it on and initial On gives 5s. Now, if I had a 2-gang plate and used flat 3&E, I could feed a L to the output of the PIR. The PIR is rated for resistive, inductive and CFL loads, so has a relay I assume (haven't heard it click yet). If the 'manual' switch is on it will supply L to the output of the PIR; if the PIR then switches on it will have L on both side (normal anyway). The load will be a 4W (about 7 - 8VA) LED (GU10, 350 lm) 120deg., 4000K in a bulkhead fitting - there's a 180 lm LED atm and it's OK for the area).

Can you see any problems with this way of wiring it?

[Andy Wade]

Some PIRs require two cycles - off-on-off-on - to activate the manual override. Have you tried that?

Yes.

That doesn't automatically follow, although I've never encountered a PIR that didn't use relay switching.

No, I've done similar with no problems. For a safe switching arrangement make up a gridswitch assembly with one DP switch and one SP. Then mains feed via DP switch to PIR 'input' as normal - to give safe isolation for lamp replacement and mechanical maintenance - and your manual switch wire via the SP switch, taken fom the load side of the DP switch, obviously. Label switches appropriately.

[John Rumm]

Should be fine. You can wire it like:

[tabbypurr]

Lots have used triacs

ditto

seldom are such precautions taken

NT

[Adrian]

Have you tried switching it off and on rapidly? That often puts it to a manual perma-on.

Failing that, train a spider to run about in front of the sensor.

[spuorgelgoog]

Or if grid switches do not appeal, "Sink/Bath" switches for water heaters are available in this configuration.

Owain

[PeterC]

No, but just have and it doesn't work. Pitty, it would have been the easy way.

I do want at least SP isolation on the L - any ordinary light switching will be SP, including the MCB and the only way is the DP RCD in most cases. The simple way would be a 2-gang, 2-way plate. Actually, if the L to common for Manual was fed via the NC side of the Auto switch, the Auto would have to be Off for the Manual to work. With both switches Off, the supply would be as isolated as any other lighting supply.

[PeterC]

Cheers - that helps. At one time I could do fairly complex stuff in my head, but lack of practice, age etc...

[PeterC]

Did you get that idea via the web?

[ARW]

Is that really needed when you can turn off and lock off (not that anyone locks off on domestics) the lighting MCB?

[spuorgelgoog]

It can be useful, if not needed for safety, for DP isolating of outside lights in case any dampness causes low insulation N-E which would trip an RCD.

Owain

[John Rumm]

I make sure all my outside electrics have their own RCD...

[PeterC]

Done the front one now. 4W, 350lm, 4000K GU10 @ 120 deg. lights the area well and isn't obtrusive from the sides. Used a 2-gang, 2-way plate and flat 3&E. It is a relay - can hear the click when close to it. When I took off the plate next to it (does hall and landing) found that the pattress was falling apart - it had been screwed down over a void, so now all of the cables have to come out and the holes redrilled when the filler has dried out. The back light needs moving along about a yard - somehow there's another shed in the way.

[newshound]

Exactly my reaction! Saves having to think about it (and much clearer than my sketch on the back of an envelope would have been).