Bathroom light switch question

[mooncat]

We have a pull chord bathroom light switch - I replaced the switch about 5 or 6 years ago, and it's been working fine until the last couple of months. Now, randomly, the circuit keeps tripping and we have to go down and flick the switch on the fuse box back on. It can go a week or two without doing it, and then trip two or three times in one day. By process of elimination (what we were doing at the time) we're pretty sure it's the bathroom light that's doing it for some reason.

I took the switch casing off today to see if anything had come loose, and the wiring goes as follows - one thick grey cable coming out of the ceiling with a green, red, and black wire coming out of it. Another slimmer grey cable coming out of the ceiling with a single red wire coming out of it. When I replaced the switch a few years back, I drew a diagram of how the old switch was wired before replacing it, and then put the new one on exactly the same way, and as I mentioned, it's worked fine for the last few years. The green is wired into the earth terminal at the top of the switch. The single red cable goes to Load L, and the red cable that's in with the green and black goes to (I assume) Supply L and then in a sort of bridge over to N. It doesn't say supply on it, but it's definitely L and N.

The black wire is not attached anywhere - it's just loose in the socket. I don't remember if that was the case when I replaced the switch, and that's my question really - should the black wire be attached, and if so, where? Could that be shorting the light and tripping the fuse? All the other wires are nice and tight in the terminals, so I'm not sure how the black has come loose (if it has).

 

[Lurch]

You need to look at where the wires go and determine what the functions are, there is no standard for putting wires in things, they could do anything. The black might be connected to nothing, it might be a neutral, it might be a switch wire, or it could be something else. The bridge/link sounds odd, considering nothing is connected. There is something that it could be, but if it is wired how you say it is the light wouldn't work (or possibly a fan). Either way, if the black does something and it isn't connected then something shouldn't work.

As for the fault, it is unlikely to be in the switch anyway, it will more likely be the light fitting itself.

 

[Evans Electric]

 Hi Moonperson ,

What is tripping at the board ?    Is it the lighting circuit breaker  (MCB)   or  is it an RCD ? 

As Lurchio says , your fault is more likely to be at the light fitting .  Is it the sort with a heat producing lamp in it ?

 

[mooncat]

Hi

It's an RCD (I think) - the fuse box was replaced recently as we had a new kitchen put in and I think it's RCD protectors. When it trips it takes out all the ceiling lights on the upper two floors (three storey house) and some of the sockets in the kitchen. The electrician who replaced the fuse box and put some new sockets  / circuit in the kitchen came back and checked all his work to see if there was anything loose / touching and it was all ok, and by process of elimination (what we're doing when the circuit trips) I"m pretty sure it's the bathroom light.

It's not a heat producing one, just a normal bathroom light with an energy saving bulb in it.

 

[Evans Electric]

Is that Black wire stripped back as if it was connected at sometime ?  

Could it have been touching the earth terminal at the back of the box.?

Its the RCD thats tripping which means its reading a   L to E      or N to E  fault .

Is there a fan in there that works when light is switched on  and continues to run after , for some minutes  ?

 

[mooncat]

The black is stripped as if it was connected at some point, yes.

Don't think it could touch the earth terminal, no - it's over the other side of the socket and hangs down a wee bit, whereas the earth is right up against the ceiling.

There is a fan in the bathroom but we've never used it in the last nine years, and the previous owners didn't either as it was too noisy. It (the fan) is switched off by a switch (like a light switch) in the loft, but I'm wondering if the bathroom light would also turn the fan on if the fan switch in the loft was on, and it's actually that that's causing the issue?

We have lights over the bathroom mirror which are working fine, and all the other overhead lights upstairs don't trip the switch, so at the moment we're just not using the main overhead bathroom light.

 

[Lurch]

If the fan is off then it shouldn't be causing an issue, but that is assuming it is an isolator wired correctly that is off.

Might be time to get the bathroom lighting tested if you have narrowed it sown to that area.

 

[mooncat]

Have just tried the light to see if it's still tripping, and it's not working all now, but neither is it tripping the rest of the lights. Which makes me think that loose black wire should be connected to something, so I presume it must be into load N as it's the only free one. And if it was getting loose, would that explain the random tripping?

(we are also going to get the wiring tested very soon when we get some new lights)

 

[Doc Hudson]

There is no Neutral 'N' required at a switch, just a live in, and a switched live out to the load.  I would have thought the Red & Black from the twin & earth grey cable would have been the standard switch cable for the light fitting and the single red would have been a switch live to trigger the fan (when it originally worked). So the Red (of the twin cable) would be into one side of the switch {possible called 'C' or 'L1'}  and the Black (of the twin cable) into the other side of the switch {possibly called 'L1' or 'L2'}.  Also the single Red cable would be in the same terminal as the black. If I understand that when you say its not working now you mean the light is not working that would definitely point to the black being the switched live out.  Confusion can arise because light switches can be labeled in different ways depending upon the manufacturer. and if it is a one way or two way switch.

Some call them  'C','L1','L2'   others called  'L1','L2','L3'.

supply in   'C' / 'L1' 

one way out  'L1' / 'L2'

two way out  'L2' / 'L3'

Actually just re-read your post, you mention 'Load N'?  That sounds more like a double pole shower switch than a light switch?

Doc H.

 

[Lurch]

Actually just re-read your post, you mention 'Load N'?  That sounds more like a double pole shower switch than a light switch?

Could be a 20A DP switch. We had them in my house when we moved in as the second pole did the fan, otherwise if you just commoned up the fan trigger the lights would come on in the other bathroom. Used to do this in new houses too when I was an apprentice. Pretty standard way of wiring a central fan.

@mooncat should stop just assuming though, if you don;t know get someone in to look at it properly. Do not just start prodding cables in willy nilly. I would assume the only place it shouldn't go is the place you suggested, if we're assuming things.

 

[kerching]

Could be a 20A DP switch. We had them in my house when we moved in as the second pole did the fan, otherwise if you just commoned up the fan trigger the lights would come on in the other bathroom. Used to do this in new houses too when I was an apprentice. Pretty standard way of wiring a central fan.

Yep.....that one caught me out when I was a ,'wet behind the ears' apprentice back in the 70s

 

[Lurch]

Yep.....that one caught me out when I was a ,'wet behind the ears' apprentice back in the 70s

When we first moved in we had someone come and change the board, they split the lighting into up and down. No borrowed neutrals so it was all fine, until you turned one of the lighting circuits off and then turned both bathroom and downstairs toilet lights on at the same time. Then you could operate the entire upstairs lights from the downstairs toilet! Still got to get round to fixing that....

 

[mooncat]

Yep, I'm not going to start messing about poking wires in without knowing what I'm doing. No idea what sort of switch it is, or if the fan was originally wired to it, but inside is a brown 'box' with load L and N closest to me and then L and N at the other end. When the spring went I took the old switch off and took it to the shop and bought the exact same one and wired it in exactly the same way as the old one as wired. I basically just copied what was there before - correct or not!

The shower isn't electric, but whether it's a shower switch, I don't know.

I've tied up the chord so I"m not tempted to try and turn the light on and am going to leave it to the electrician. Is it worth putting some electrical tape over the exposed end of the loose wire so there's no chance of it touching anything else inside the socket? Or does it not matter as the light is off / not working?

Thanks for all the answers!

 

[Lurch]

Is it worth putting some electrical tape over the exposed end of the loose wire so there's no chance of it touching anything else inside the socket? Or does it not matter as the light is off / not working?

Could argue it either way, up to you. Wouldn't hurt to just pop a piece over it, but like a piece of tape, not half a roll over everything.