standalone PIR

[IanJ]

I have a standard 150W security light on the back of my house high on the wall, wired via a standlone PIR halfway down the wall. This used to be powered via a plug in my daughter's bedroom, and worked fine.

I wanted to move the power source to the loft, to hook this light in with a couple of new lights I've fitted and generally tidy things up. I thought I could use the existing single run of 3-core cable to switch the live via the PIR, but it doesn't work

If I bypass the PIR and hook the two cables together (live feed + 'switched' live), the light works fine. But if I hook them into the PIR, it doesn't. So I assume the PIR needs a neutral feed to work? (The previous owner fitted this, so I don't have the installation instructions.)

There are three wires at the junction block inside the PIR - brown (I assume for live in), white (I assume for switched live) and a couple of blue wires looped together (I assume for neutral), plus an earth block.

So do I have any alternative to running a separate cable?
Are there any standalone PIRs on the market that could just be used to switch the live?

IanJ

 

[breezer]

they all require live, neutral and earth ro work, as you assumed the white wire is a switched live, so the anser to your question is no.

you will have to run a new sutable cable/ s

 

[IanJ]

Thanks Breezer - now I just have to persuade the wife that this was part of my plan in the first place ...

 

[IanJ]

One more question ... the light is connected via a JB in the loft, and it's obviously just the live I want to switch via the PIR.
So, can I use the earth wire in the existing 3-core cable to the PIR to act as the neutral supply to the PIR?
The PIR wouldn't be earthed, but as the earth wire just goes to a terminal block, I assume it doesn't need to be.
The light would still be connected to neutral and earth via the JB in the loft.

Would that work? Would it be safe?

 

[ban-all-sheds]

One more question ... the light is connected via a JB in the loft, and it's obviously just the live I want to switch via the PIR.
So, can I use the earth wire in the existing 3-core cable to the PIR to act as the neutral supply to the PIR?.

You can, but you may not.

Would that work?

Yes.

Would it be safe?

No.

 

[IanJ]

OK ... I won't do that then.
But just out of interest (and sorry if this is a stupid question) what's unsafe - presumably that the 'earth' cable isn't sheathed within the outer cable insulation?

Thanks for the advice.

 

[IanJ]

Thanks for the info.

Yes, the PIR is double-insulated, so it doesn't need to be earthed.

So if I make sure the exposed 'earth' (now neutral) cable within the PIR and within the JB in the loft are properly sleeved and labelled, then make sure the whole thing is fused appropriately ... I take from what you say that the job would be safe (i.e. not about to burst into flames), although against regulations and not recommended practice. Is that right?
I can live with breaking the rules as long as I live to tell the tale ...

 

[securespark]

It is unsafe, double insulated or not - for the following reason (at least)

The earth wire (cpc) is only intended as a cpc and not as a phase conductor. Imagine using it as such and then someone else coming along believing it to be a cpc..........

 

[IanJ]

Fair enough.
Would it be safe enough to do this as a temporary measure for a week or so, until I've had chance to run the new 4-core cable (providing cable is sleeved and labelled, and I make notes on what I've done)?
I'd prefer not to be without the security light in the meantime, but I don't want to do it even temporarily if there's a risk of fire etc.

 

[ninebob]

I guess it comes down to the saying - "there's nowt so permanent as a temporary job".

It won't take you too long to obtain and fit the correct cabling, so my advice would be to do that first.

 

[breezer]

my late father would say, "there is nothing so temporary as a permanent job"

so the answer is NO, wait untill you get the 3 core and earth, that way you save time, because you are only doing the job once, it will be the correct way of doing it.

Now the crunch.

This cable run, not going outside is it?

 

[IanJ]

Thanks breezer
Cable run is inside (out of loft through ceiling, down through a corner of a bedroom inside trunking, then out through the wall at skirting-board level, straight into the PIR)
Out of interest - would that be a problem if it was outside? I assume from your question it would need to be some kind of special exterior cable?

 

[breezer]

Out of interest - would that be a problem if it was outside? I assume from your question it would need to be some kind of special exterior cable?

yes you can not run t & e outside as it will break down.

It is also why outside steel wire armoured cable is used \ as it is designed to go outside, buried