PIR Sensor

[JohnW2]

Thanks for that. For the existing wire, what I mean is there was a single light on the old soffits, which has been removed whilst new soffits were put up. There is now the old existing single length of T & E wire in the soffits, coming from the hallway switch.

Fair enough. Thanks for clarifying.

My query is if I use that for the new PIR, I would have to cut the earth at the PIR as there is only 2 inputs and 2 outputs.

I'm not really sure what you mean by 'having to cut the earth' at the P|IR. You would surely also have to 'cut the neutral and the live', to connect them to the PIR, wouldn't you? If the PIR does not need an earth, and if there is no terminal in the PIR to which to connect the earth wire you would have to use a little bit of connector block or suchlike to connect the earth wire to.

However, this "2 inputs and 2 outputs" you keep mentioning is very unusual. Most commonly, PIRs have four terminals - a ('permanent') live 'input' (from house/switch), a ('switched live') output [for light(s)], a neutral (common to both the incoming power and output to lights) and, finally, a terminal to which to connect the earths (of both incoming and outgoing cables), even if the PIR itself does not need the earth. Could you possibly provide us with a photo of the connections to the PIR (or, if that is not possible, tell us the make and model of the PIR)?

... Then daisy chain from there, to the row of downlighters. Therefore because the PIR only has 2 inputs and 2 outputs, I cant use 3 core and earth, is that correct?

I thought that the PIR was going to be at the end of the run of lights, and that the 'existing' T+E cable (which supplied the previous light) would not be long enough to reach it. However, if that cable will reach the PIR then, yes, you could do as you say. As above, even if the PIR really does not have anywhere to connect the earth, you can still use T+E, but would then have to use something to connect the earth wires safely to. In fact, to be strictly compliant with the Wiring Regulations, you must run an earth to the PIR and to each light, even if none of them actually need an earth.

If I wire it the way I mentioned with the T&E, am I correct in saying that the lights will come on when sensor is activated, & I will need my switch on all the time?

Yes, the switch would then only serve as a means of disabling ('switching off') the whole setup. With that arrangement, there would be no way of switch the lights 'permanently on'.

Or…am I best just wiring straight to the lights, forget about the PIR for now, & install a smart switch with timer?

Only you can answer that one - it depends what you want, since the functionality of a PIR and 'a smart switch with timer' are very different. However, to wire with the PIR really is very straightforward.

Kind Regards, John

 

[scottpetrie]

Okay thanks. Yes the existing cable would reach the end, would just need re-routing in the loft first (im in a bungalow). Was just trying not to for easiness! I will get a pic soon, but am away from home for a couple of days. Its a LAP motion sensor from screwfix. If I used the existing T&E, would I just join the earths with a connector at the PIR, then continue on as normal to the rest of the lights (they have 3 terminals)? Only thing confusing me is the PIR having only 4 terminals (2 in & 2 out).

 

[bernardgreen]

Earths not shown but must be run to all lights and PIR even if it is not required. Reason is to protect from cable faults

 

[scottpetrie]

I will get pics of the sensor and the switch once Im home, but if I changed the length of cable from the switch to 3 core and earth, where would the additional live go in the switch? If I did it that way, could I run that cable to the PIR, permanent live in, switched live out, neutral in/out, join the live to the T & E (thats going to the lights) and join the earth to the T & E (thats going to the lights) then continue on the T & E to the remaining lights?
Would that then mean that the PIR is permanently live and the lights can be switched on/off as normal, and when they are off the PIR would still kick in when its triggered?
Thanks for all your help

 

[JohnW2]

Okay thanks. Yes the existing cable would reach the end, would just need re-routing in the loft first (im in a bungalow). Was just trying not to for easiness!

Fair enough. I misunderstood, and thought you were implying that the existing cable would not reach the PIR.

I will get a pic soon, but am away from home for a couple of days. Its a LAP motion sensor from screwfix.

OK. There are actually four LAP motion sensors on the Screwfix website, so I don't know which one. However, none seem to come with useful instructions (on-line), so I'm not sure it would help to know which one you have! As you will realise, my interest is in ...

.... Only thing confusing me is the PIR having only 4 terminals (2 in & 2 out).

... since, as I aid, that's not an arrangement I've ever seen. As I said, I'm used to seeing 3 or (usually) 4 terminals - one 'live in', one 'live out', one neutral (for both 'in' and 'out') and, usually one for the earth. However, if there really is nowhere for connecting an earth, that alters nothing, other than that you'll have to provide some sort of connector at the PIR to connect the 'incoming' earth to that going to the first of the lights in the chain.

If I used the existing T&E, would I just join the earths with a connector at the PIR, then continue on as normal to the rest of the lights (they have 3 terminals)?

Indeed, just like that - and all could be done with 2 core + earth cable.

I obviously don't know how the cables will be routed but, if they are 'exposed' (to sunlight and 'the elements'), someone will undoubtedly point out to you that T+E cable is not really 'suitable for' outdoor use (even though countless people use it for outdoor lights).

Kind Regards, John

 

[scottpetrie]

Okay thanks. So thats fine I can link all lights together and PIR. My final question, do I need to change the length of cable from the switch to PIR to 3 core and earth, to provide the PIR with a permanent live (so the lights switch on/off as normal but PIR also stays active when switch is off during the night)? If so where does the extra live go to on the switch? Ill post pics soon of whats there already.
The cables will be run up in the soffits, so basically in the loft and are exposed to no elements.

 

[JohnW2]

Okay thanks. So thats fine I can link all lights together and PIR. My final question, do I need to change the length of cable from the switch to PIR to 3 core and earth, to provide the PIR with a permanent live (so the lights switch on/off as normal but PIR also stays active when switch is off during the night)?

IF you want to be able to switch the lights on ('permanently')/off (independent from the PIRE control) then, yes, you would need 3-core+earth cable from the switches to PIR but, as has been illustrated, you would also have to change the single switch to a 'double' ('2-gang') one, since you would also need a switch to disable 'everything' (including the PIR) - not the least in case something went wrong with, or work needed to be done on, the lights/PIR/wiring.

The cables will be run up in the soffits, so basically in the loft and are exposed to no elements.

Fair enough.

Kind Regards, John

 

[scottpetrie]

Aah Okay I get it. The switch already is a 2 gang switch as it has another switch for hallway light. The PIR says it can be over-ridden by flicking the switch on/off/on. Maybe Ill just need to do that and leave the switch on during the night to keep the PIR active. I thought of a smart switch so I could have the lights on a timer but dont think that would work with the PIR as all it would do is switch on or off and not double switch to override it.
What would happen if I didnt have another switch, would the PIR just be permanently on unless lighting circuit was switched off at mains?

 

[Taylortwocities]

…

 

[Taylortwocities]

What would happen if I didnt have another switch, would the PIR just be permanently on unless lighting circuit was switched off at mains?

I think you are missing an essential point.
You have a switch which will provide power or no power to the PIR. When the switch is off, the lights are off. When the switch is ON the PIR is enabled. If you want the lights on all the time then you do the on/off/on malarkey.

You didn’t mention the pulse over ride feature. Nobody round here would buy a LAP product

You won’t need 3-core and earth. Thd cable u have is ok.

 

[scottpetrie]

Yeh thats what I thought. I just wondered if I switched the switch off, do I then need a permanent live to the PIR for during the night when lights are off?

 

[JohnW2]

Aah Okay I get it. The switch already is a 2 gang switch as it has another switch for hallway light.

OK. If you wanted to do what I was talking about, you could change it to a 3-gang one, hence providing the required additional switch/'gang'.

The PIR says it can be over-ridden by flicking the switch on/off/on. Maybe Ill just need to do that and leave the switch on during the night to keep the PIR active.

That would be the simplest approach, and would only require T+E cable from switch to PIR. The 'flicking to over-ride PIR' facility (which many/most PIRs have) usually works fine. The only real downside is that if (like me) you get 'fraction-of-a-second power cuts', that can sometimes put the PIR into it's 'over-ridden' (lights permanently on) mode - but, if your PIR has that facility, that problem exists regardless of whether you ever use the facility yourself!

I thought of a smart switch so I could have the lights on a timer but dont think that would work with the PIR as all it would do is switch on or off and not double switch to override it.

As you imply, although 'do-able', that would make things more complicated.

Kind Regards, John

 

[JohnW2]

Yeh thats what I thought. I just wondered if I switched the switch off, do I then need a permanent live to the PIR for during the night when lights are off?

The PIR cannot work (i.e. turn the lights on when triggered by motion) if it does not have a 'permanent live' supply.

Kind Regards, John

 

[JohnW2]

You didn’t mention the pulse over ride feature.

See post #9.

Nobody round here would buy a LAP product

All of my PIRs are 'at least as bad' as LAP ones (look the same {probably come from the same Chinese factory}, but unbranded and cheaper) and, for what it's worth, have always served my purposes satisfactorily and reliably. Experiences will obviously vary.

Kind Regards, John

 

[EFLImpudence]

I think it is confusing Scott to keep calling it a permanent when the switched-live is normally left (permanently) ON for the operation of the PIR.

Turning OFF the switch will turn OFF the system.