Switching the Neutral?!!?

[Greenie9657]

Hi all,

I've just been to my Nans to sort out a light switch that had fell off the wall (no back box, faceplate screwed straight into the wood which has now rotted). When I took the switch off to mount it in a PVC back box it looks like whoever wired it up has switched the neutrals through the light switch.

Theres one continuous T+E from the source, then the black breaks through the switch but the red is continuos up to the light fitting. It's never been touched since she bought the house well over 15 years ago.

It's a shed light so one switch and one light.

I've never seen it before and never even heard of it. It obviously works but is it safe?

The obvious safety would be if someone was to change the actual light fitting and guessing it was dead because the switch was off.

Regards

 

[JohnW2]

Theres one continuous T+E from the source, then the black breaks through the switch but the red is continuos up to the light fitting. It's never been touched since she bought the house well over 15 years ago. ... It's a shed light so one switch and one light. ... I've never seen it before and never even heard of it. It obviously works but is it safe?

If it is as you say, and if the colours have been used correctly then, as you say, the switch appears to be switching the neutral and (for the reason you go on to mention), it is not safe.

However, are you certain that the cable you mention is the feed from the supply, and do you have the means of determining whether the colours have been used correctly?

Kind Regards, John

 

[Greenie9657]

Thanks for your reply John,

The wiring is wrong on all fronts TBH.

The feed into the light switch comes for a socket on the adjacent wall in the joining garage. No FCU just straight from the socket. t+e clipped to the wall.

 

[JohnW2]

Thanks for your reply John, The wiring is wrong on all fronts TBH. ... The feed into the light switch comes for a socket on the adjacent wall in the joining garage. No FCU just straight from the socket. t+e clipped to the wall.

Oh dear - that's not good. I don't think you really have any safe option other than to have it all redone properly - with an FCU and correct polarity of switching!

Kind Regards, John

 

[kai]

In a pinch, you could use a DP switched FCU (with 3amp fuse) as a switch, as both poles will be switched.

 

[JohnW2]

In a pinch, you could use a DP switched FCU (with 3amp fuse) as a switch, as both poles will be switched.

I suppose so, but he would at least have to take the existing switch 'out of circuit' (e.g. by putting both conductors into one terminal) - or else there would be the risk that someone would switch it off with that switch (with the SFCU still 'on') and think that the lamp was isolated.

'Doing it properly' is obviously the best way to go. If there's enough slack for the red at the switch to be cut and connected to the switch (with the two cut black ends joined in a connector block, he could keep existing switch and cable and merely add an FCU.

Kind Regards, John

 

[plugwash]

Provided there is enough slack in the wires I'd replace the existing switch with A FCU, this would provide overcurrent protection and double pole switching.

I'd also want to check the rest of the shed wiring though to make sure it had adequate overcurrent protection and was wired in a suitable cable type.

On a related note personally I would not rely on a lightswitch as a means of isolation even if I was pretty sure it was wired correctly. If I have to remove the remains of an exploded lightbulb I turn the whole circuit off at the CU.

 

[JohnW2]

Provided there is enough slack in the wires I'd replace the existing switch with A FCU, this would provide over-current protection and double pole switching.

Yes, that would be a little simpler than what I suggested - provided it was not considered likely that any further lighting would be required in the future (in which case retaining the switch and having a separate FCU would make sense).

I'd also want to check the rest of the shed wiring though to make sure it had adequate overcurrent protection and was wired in a suitable cable type.

Agreed. That obviously should include confirm that the cabling of lighting circuit has correct polarity (insulation colour-wise).

On a related note personally I would not rely on a lightswitch as a means of isolation even if I was pretty sure it was wired correctly. If I have to remove the remains of an exploded lightbulb I turn the whole circuit off at the CU.

So would I, but we both know that a substantial proportion of the general public would probably rely on the light switch - which is obviously why the present situation should not be allowed to persist.

Kind Regards, John