Drill bit meets hidden flex

[F]

I put a drill through the wall into the garage yesterday and hit a flex that had been buried in the garage ceiling and which ran between the security light and the PIR that feeds it. The fuse on the fused spur that feeds the PIR didn't blow and I didn't realise what had happened until I went into the garage, tried to prise some 'silicone' out of the way with a screwdriver and got a bit of a tingle. The 'silicone' was the chewed up white flex.

I'm not sure why I should get a tingle from the flex when the PIR was 'off' due to it being the middle of the day.

Anyone?

And what would be an acceptable repair? One of the damaged ends is very short and there's no slack to pull through.

[ARWadsworth]

The PIR has a permanent live!

Crimps/replace cable?

[F]

So only the neutral's switched?

The (existing) cable was routed through/under a new roof and I can't get at that routing so it looks as though I'll have to crimp. Unless a connector strip and insulation tape, then push the repair into the void above the ceiling, is good enough?

[The Natural Philosopher]

yes: BTTGTTS

[John Rumm]

No, the PIRs have three connections; perm live, switch live and neutral.

The dangerous bodge used on some of these installations uses three core flex, and repurposes the earth wire as something else (something you are not supposed to do to a earth/CPC even if you sleeve the wire)

(three core and earth cable would be the appropriate choice)

As long as the repair is either enclosed in heatshrink or in small plastic box like a chockbox etc.

[F]

I'm confused...

The flex I hit was the one between the PIR and the lamp, as opposed to the one between the fused spur and the PIR. I would have expected the live in question to be 'off' as it was daylight and the PIR wouldn't have switched it to 'on'.

[dennis]

It depends on where the live is feed from.

If the live feed from the CU goes to the PIR first there may only be switched live and neutral to the lamp.

However if as on one of mine the feed goes to the lamp first there will be permanent live, switched live and neutral in the cable. Quite common when a PIR is added to an existing lamp.

There is probably an earth too, but it can be missing.

[F]

It's CU > ring > fused spur > PIR > lamp. From the fused spur onwards it's all in 3-core (live, neutral, earth) flex. The PIR is this one:

[dennis]

the live and neutral aren't swapped on the PIR output then.

[Adam Funk]

Think about it like "loop-in" ceiling light wiring: there's an always-on live running from the light fitting to the wall switch (or PIR), and a switched live running back from the switch (or PIR) to the light fitting.

John & Adam: Do all PIRs need a neutral as well as live coming in & switched live going back? I think I've seen two-connection ones (not counting the earth) in the past, although I could be wrong.

[Toby]

Further on, you say the connection is SUPPLY----> PIR -------> Lamp

You have drilled into the cable between the PIR and the lamp.

The PIR may not have a neutral connection, it may rely on leaking a small current through the lamp to power the PIR electronics, if this is the case, you could then get a tingle from this leakage current, if it says it is not suable for fluorescent/low energy lamps, then this is almost certainly the case)

If the PIR is drawing under 30mA then it probably wouldn't trip and RCD either.

Repair in order of preference

1. Replace the cable if practical
2. Replace the easiest to replace section, joining the cable with crimps if the join is not going to stay accessible
3. insert a short length of cable and make two new connection (crimped if the joints are got going to stay accessible)

[John Rumm]

"All" is a strong word ;-)

Most will require a L&N connection to function. However some designed for installation in the location of an existing switch may find a neutral reference by drawing a small amount of current through the lamp itself. Generally these only work properly with traditional filament lamps.

[John Rumm]

It depends on how these things have been wired... If the wiring delivers power to the PIR first, then it is possible that there is only a switched supply to to the lamp. In which case you either have one of the rare PIRs designed to work without a neutral, that are never truly "off" and pass a small current through the lamp at all times, or, it has been incorrectly wired with the neutral being switched rather than the live.

Personally I tend to run 3&E between all the parts of PIR switched systems so that you can add parallel PIRs or override switches anywhere, and you have some flexibility for future modifications.

[F]

Thanks for all the feedback. I'll check that the connections are correct and put the repair into a chockbox.

[Toby]

Will the joint be accessible later, or will it be covered over, if it is going to be covered over with plasterboard etc.. you need to crimp it.