Confusing switched live / neutral?

[jonmc1980]

I just have a question concerning wiring a light fitting. What happens if a light is wired incorrectly i.e. switched live / neutral confused. Does it work or does the s**t hit the fan when switched on?

I ask as a lad I work with was telling me he switched a light but lost track of which wires were which (old cables) and he just went ahead. I thought it sounded a bit dangerous, but wasn't exactly sure of what would happen if they were mixed up

 

[rebuke]

If you treat the switched live as a neutral, then it will go bang when you turn the switch on, since you create a short circuit (live connected to neutral through the switch without any load).

If you're lucky, all that will happen is the MCB will trip - however, on an older system with rewireable fuses, there's a small risk it may not trip quickly enough to prevent the cables melting / catching fire, and regardless of system you're quite likely to weld the contacts of the switch closed (and obviously totally fry a dimmer switch)...

 

[ban-all-sheds]

Depending on the type of lighting circuit, and which conductors get misplaced, you could also end up with part of the circuit dead, or part of it needing that light on for the rest to work, or lights coming on, but dim....

 

[flameport]

Another possible error is where the neutral is switched instead of the live. The light and switch will work - but when off, the lampholder is still live. Unsafe as the person changing the lamp could get a shock.

 

[sparkyspike]

The scenario your mate is talking about is almost certainly what flameport has described - mixing sL and N at the light fitting will mean that the lamp will still work. With BC fittings, this isn't so serious - although it still should be identified correctly for various reasons. With an ES fitting it is much more serious as you could touch the live part of the bulb when screwing it in!

 

[Greenspot]

Evening everyone. Need some advice re something which doesn’t make sense. I have a greenbrook lighting connector which is wired as you would do a standard ceiling rose. I’ve now got issues with one set of lights. The wiring I’ve done (I know the looped live and switched live are the ‘wrong way’) is attached as the photo in bright green but the image I have from a well know screw shop shows something odd on their photo in safe green. It shows a neutral as a switched neutral. Not sure if that is the right term. Any help would be appreciated.

 

[EFLImpudence]

You are correct. The screw shop picture is wrong.


As for your wires being 'the wrong way round', some people like to do it that way so you can tell which cable goes to the switch (when not as obvious as those connectors).

 

[Greenspot]

You are correct. The screw shop picture is wrong.


As for your wires being 'the wrong way round', some people like to do it that way so you can tell which cable goes to the switch (when not as obvious as those connectors).

Thank you for helping me here. It’s as I thought so basically the shop that you can buy screws and fixings at has an incorrect image?

 

[sparkwright]

You are correct. The screw shop picture is wrong.


As for your wires being 'the wrong way round', some people like to do it that way so you can tell which cable goes to the switch (when not as obvious as those connectors).

They also like to do it so the perm live terminal has at least one brown in it, and the switched live terminal has a brown in it as well.

 

[EFLImpudence]

I don't follow:

They also like to do it so the perm live terminal has at least one brown in it,

How could it have none?

and the switched live terminal has a brown in it as well.

Why would they particularly want that?

 

[Sureitsoff?]

further to this thread I contacted greenbrook and they have just confirmed that their pic is wrong and they are going to change it !!