PIR occupancy switch and LED battens

[rafletcher]

I want to fit an occupancy sensing switch in our outhouse. The lighting is two mains LED tubes that are slotted in as direct replacement for fluorescents, no messing about with ballasts, as in these (recommended btw)..

https://led.me.uk/t8-led-replacement-tube-4-1200mm-in-cool-white-6000k

Being mostly ignorant of things electronic, and capable only of simple electrical work, would this switch

https://www.lightshopdirect.com/wall-mounted-pir-sensor-with-switch-ip20/?aditem=948&gref=112259818279&gdev=t&gloc=1006490

work with that load? I do have live, neutral and earth at the current manual switch.

[Kim]

If you've got a neutral at the switch position, I expect it should be fine.  The tubes won't be anywhere near its load rating.

[Diver300]

Being mostly ignorant of things electronic, and capable only of simple electrical work, would this switch

https://www.lightshopdirect.com/wall-mounted-pir-sensor-with-switch-ip20/?aditem=948&gref=112259818279&gdev=t&gloc=1006490

work with that load? I do have live, neutral and earth at the current manual switch.

Just to be clear, any switch, not just a PIR, has to have switched live. The textbook way to wire a simple switch is with two brown (red in old colours) cores in a wire, plus earth. One core is live, one is switched live. However that needs a different type of cable for a just a few wires in each house and it's very common that switches are wired with the more readily available brown + blue (red + black in old colours) and the blue (black in old) sometimes has a coloured sleeve to show what colour it's supposed to be, but not always.

If your switch has a three core cable, one of which is earth, going to it, it can't have live, neutral and earth.

You need 4 cores to go to the switch for a PIR one. The 4 cores are live, neutral, switched live and earth. 4 core (Triple and Earth) cable is usually used for that.

It's very common for the light fitting or the ceiling rose to have all 4 connections (live, switched live, neutral and earth) and you are likely to have to run a triple and earth cable from the light fitting to the switch.

[grams]

I'm going to assume an outhouse is more likely to have the incoming mains going through the switch than the ceiling rose arrangement found indoors.

One foreseeable problem is that these things detect motion, not occupancy. If you sit still for a long time (ahem) it goes dark.

[Jurek]

I'm going to assume an outhouse is more likely to have the incoming mains going through the switch than the ceiling rose arrangement found indoors.

One foreseeable problem is that these things detect motion, not occupancy. If you sit still for a long time (ahem) it goes dark.

Can I correct you grams. They don't detect motion. They detect temperature change.

[fuaran]

I've got one of those tubes in the shed. Connected to a PIR sensor like this. https://led.me.uk/white-pir-infraed-motion-sensor-light-switch-st15-for-led-and-energy-saving-bulbs
That goes on the wire between the switch and the light, so could give more options for where to put it. I have it just below the ceiling. Can adjust the angle, so it points where you want.
And adjust the time it stays on for. Though yes, if sitting still for too long, have to wave your arms about...

Was not too complicated to wire up, once I figured which way round the wires go.

[rafletcher]

Being mostly ignorant of things electronic, and capable only of simple electrical work, would this switch

https://www.lightshopdirect.com/wall-mounted-pir-sensor-with-switch-ip20/?aditem=948&gref=112259818279&gdev=t&gloc=1006490

work with that load? I do have live, neutral and earth at the current manual switch.

Just to be clear, any switch, not just a PIR, has to have switched live. The textbook way to wire a simple switch is with two brown (red in old colours) cores in a wire, plus earth. One core is live, one is switched live. However that needs a different type of cable for a just a few wires in each house and it's very common that switches are wired with the more readily available brown + blue (red + black in old colours) and the blue (black in old) sometimes has a coloured sleeve to show what colour it's supposed to be, but not always.

If your switch has a three core cable, one of which is earth, going to it, it can't have live, neutral and earth.

You need 4 cores to go to the switch for a PIR one. The 4 cores are live, neutral, switched live and earth. 4 core (Triple and Earth) cable is usually used for that.

It's very common for the light fitting or the ceiling rose to have all 4 connections (live, switched live, neutral and earth) and you are likely to have to run a triple and earth cable from the light fitting to the switch.

I think it is live, neutral and earth - red, black, yellow/green because... the supply comes in to an RCD double socket, and the lights are plugged into one of those sockets with a conventional plug. The cable from that plug goes via the switch with a switched live. Apologies for the less than full disclosure! Not very professional but it’s lasted 20 years thus far.

[rafletcher]

I've got one of those tubes in the shed. Connected to a PIR sensor like this. https://led.me.uk/white-pir-infraed-motion-sensor-light-switch-st15-for-led-and-energy-saving-bulbs
That goes on the wire between the switch and the light, so could give more options for where to put it. I have it just below the ceiling. Can adjust the angle, so it points where you want.
And adjust the time it stays on for. Though yes, if sitting still for too long, have to wave your arms about...

Was not too complicated to wire up, once I figured which way round the wires go.

Damn, I should have looked there too! Ta.

[grams]

Can I correct you grams. They don't detect motion. They detect temperature change.

They detect sudden changes in temperature* consistent with movement. The electronics are designed to filter out smooth changes consistent with actual changes in temperature.

(* double pedantically, IR radiation)

[Diver300]

I think it is live, neutral and earth - red, black, yellow/green because... the supply comes in to an RCD double socket, and the lights are plugged into one of those sockets with a conventional plug. The cable from that plug goes via the switch with a switched live. Apologies for the less than full disclosure! Not very professional but it’s lasted 20 years thus far.

Nothing to apologise for. It's your shed!

If power comes from a conventional plug to the switch, there has to be live, neutral and earth, and the wire out to the lamp will be switched live, neutral and earth, so all 4 are available at the switch.

There's nothing wrong with wiring the live and neutral via the switch. All it means with a simple switch is that the neutral and earth wires have to use the switch box as a junction box. House wiring is usually done with live to the ceiling rose as a way of simplifying the installation of lights in multiple rooms, often with 2 or 3 way switching.

The plug is a really good thing to have when wiring up a switch like that. You can unplug and be certain that the switch isn't live. Don't rely on turning off the ELCB*.

You should put the plug fuse at 3 A or less if powering lights. I would use a 1 A fuse, having bought loads for just such applications, but 3 A are far more readily available.

* Turning off the ELCB is virtually certain to make it safe, but there can be very rare faults that leave it live when off.

[Jurek]

Can I correct you grams. They don't detect motion. They detect temperature change.

They detect sudden changes in temperature* consistent with movement. The electronics are designed to filter out smooth changes consistent with actual changes in temperature.

(* double pedantically, IR radiation)

Every day is a school day 

[Kim]

PIR sensors are one of those things that shouldn't work anywhere near as well as they do.  There's a little bit of magic stuff that does electrical things when the amount of IR radiation it's subjected to changes, and then a deviously cunning piece of IR optics that divides the field of view up into zones.  As an IR source moves across the field of view this causes a rapid change in received IR (as opposed to a slow one, from the room heating up), which the electronics detect.  Witchcraft.

As for controlling lights with them, it can work well if sufficient thought is given to sensor coverage and timeout duration.  It can work appallingly badly if there aren't enough sensors or their view is occluded by, say, a toilet cubicle door.

And I'm of the opinion that it's just shortsighted not to run the neutral to the lightswitch these days.  Too many smart thing options that require it.  Just fit a deeper backbox and make the junctions normally done at the rose behind the switch.

[rafletcher]

So, I bought the sensor fuaran linked to.  Rather than try and guess which wire goes where - I have L, N & E, not L, N, L - I thought I’d ask here, as the wiring diagram isn’t (to me, anyway) crystal clear...

Untitled by Richard Fletcher, on Flickr

How should I wire this? TIA.

[Diver300]

You need to have L, N and switched Live at the switch.

The connections with the colours are the internal connections from the terminal block to the workings of the PIR sensor, so they are already there. The load, the circle with the cross in it, is the light you are switching. It's a circuit diagram, not an engineering drawing, so sizes don't scale. Your light will be larger than the terminal block.

The ones underneath are the connections that you have to make.

1) Neutral goes to the middle of the three terminals

2) Neutral also goes to one side of the light.

3) Live goes to the right hand terminal, the one with the brown wire connected to the other side.

4) Switched live connects the left hand terminal, the one with the red wire, to the other side of the light.

Earth is not needed for the PIR. If there is an earth terminal on the light, that should be connected to earth somehow. There may be intermediate connectors, or not, it doesn't matter.

[rafletcher]

You need to have L, N and switched Live at the switch.

Oh dear 

[Diver300]

You need to have L, N and switched Live at the switch.

Oh dear 

I thought that you had a L, N and E cable feeding the PIR switch from an ordinary plug. If that is the case, L and N come from there.

Switched live is produced by the PIR switch and comes out on the red connector to the left.

Then a cable from the switch to the light, that has switched live, Neutral and Earth. The red / brown of the cable between switch and light is the switched live. Blue / black is neutral and that is connected the centre connection along with the neutral from the plug.

At the light, you have switched live and neutral which connect to the two connections on the light, probably marked live and neutral.

Earth wires connect to everything metal at every point. If the switch has no earth terminal, fit one.

[Feanor]

Would a diagram help?


20201121_172407 by Ron Lowe, on Flickr

[rafletcher]

Thank you