help needed with bathroom light

[terryshand]

Hi
I have been abroad working and left the builders doing a loft conversion, part of the regs was to fit a bathroom fan. The builders have gone bust.

When I switch the bathroom light off it blows BOTH lighting 6A trips in the fusebox.
I thought I'd be clever and disconnect the new fan wires which I cant get to as its buried within the new woodwork, I assume the wires come from the ceiling rose, but there are 8 cables and 21 wires including earths.

2 core, red to loop in, black to N
2 core, red to loop in, black to N
3 core, red to loop in, blue to L, yellow to earth
3 core, red to loop in, blue to L, yellow to earth
3 core, brown to L, blue to N, green/yellow to E
2 core, brown to loop in, blue to N
3 core, brown to loop in, grey to L, black to N, bare to earth
3 core, brown to L, black & grey spare, bare to earth

L has 5 wires, loop in has 6 wires, N has 5 wires, E has 5 wires. Plus the 2 for the lampholder.

The room has 2 doors so 2 switches and also a lamp with shaver socket over the basin which comes on with the main light.

There is 242V on L and loop in With respect to N or E and the last 2 cables on the list look the newest.

Its a long shot but any one got any starting point.

Please help

 

[SUNRAY]

That lot of wiring is going to take some thinking. My first guess is they have damaged cables in the building work, putting a short on somewhere.

The fact that both trips blow could again be damaged cables but 10p says there's some wrong wiring on a 2way circuit. Do you have 2 way switched lights any where else with 2 lights? my first guess is top and bottom of stairs, if so switch the light on using the downstairs switch, then switch off both trips, one at a time to to identify which trip supplies that circuit. Then switch the light off using the downstairs switch and then put it on again using the upstairs switch and again check which trip powers the circuit. My 10 p says its the other one.

Hope its not too confusing

 

[terryshand]

Yes I am confused and I dont see what the stairs light has to do with my bathroom problem.

I have 2 flights of stairs with lights at top middle and 2 at bottom and theres 4 switches that control ALL 4 lights.

 

[SUNRAY]

OK Terry
First I am trying to identify why both trips blow, as it should only affect one!

As there are 4 switches, 2 will be 2way and the other 2 will be intermediates. What I want you to do is turn both trips off then remove the switches from the wall one by one to identify which are which. 2 will have 4 terminals, these are the intermediates and should be put back on the wall and then ignored. The other 2 switches will have 3 terminals, these are the 2way and are the ones to perform my previous test on.

 

[terryshand]

That was easier done than said as I replaced the switches only a month ago and still had the notes in a book.
the switch in the hall is powered by the left trip and the switch up stairs is powered by the right trip. also the bathroom now goes off when tthe right trip is off.

Not so confused now

 

[SUNRAY]

Yep

Come across this one several times. that light circuit with 4 lights and 4 switches is badly wired and NEEDS TO BE REWIRED. It is a surprisingly popular way of wiring 2 way [or 4way!] circuits and the method is even shown on this site but I dont like it as its so easy [as in your case] to get it wrong!

Any way I dont have any instant ideas for the other problem, can you get to the cables to check for damage?

 

[electronicsuk]

Perhaps, as part of the work, the 'lighting trips', which were previously fuses or MCBs, have been replaced with RCBOs. If the fan has been installed by taking a live off one circuit with a borrowed neutral off the other, both RCBOs would trip when the fan is switched on, despite their being no fault with the fan itself.

Do the trips have a test button on them?

 

[terryshand]

I only changed the switches and put all the wires in exactly as they were in the old switches. Im glad I put lables on everything and took notes as there are spare wires in every switch.
No I cant get to any of the wiring now as that part of the loft has been floored over.

 

[securespark]

Just to eliminate one line of questioning:

When you changed all the switches, everything worked OK afterwards?

Has the bathroom fan ALWAYS tripped the circuit breakers ever since it was installed or ever since you first operated it? Or is this a recent problem?

 

[Spark123]

My 10p is on that one of the twin and earths is a switch wire and is connected across L&N, but all those wires at one point is a nightmare!
You need to start by identifying which cable goes to what. Is there access from above in a loft?

 

[terryshand]

Thanks guys, I was expecting the answers to take hours or even days, this is great.

When we went away the 2 lights in the bathroom worked properly, with the 2 switches. The fan has been added since and was running when we got home. The fuse box has not been changed yet, it has got plug in trips with a coloured handle abit like an old fashioned up/down switch. I dont have any rcd (I think thats the right letters). That was all supposed to have been done by the builders.

 

[terryshand]

My 10p is on that one of the twin and earths is a switch wire and is connected across L&N, but all those wires at one point is a nightmare!
You need to start by identifying which cable goes to what. Is there access from above in a loft?

That bit has been boarded over and I'm reluctant to rip it up as it looks like the builder has gone bust or something. I'm just thanking my lucky stars the roof was finished.

 

[Spark123]

Looks like all the wires are at the one point to stay! Is there enough room behind the fitting to fit some sort of enclosure? I personally don't like having masses of wires all in one place.
Also you mention you have some red/black wires which could have ideally have been replaced with twin and earth.
Have just re-read your original post.
The yellow cores in the 3 core sound wrong to me, how are they connected in the switches - assuming they go to the switches?
These cables should also have ideally been replaced with 3C&E
It doesn't sound like any inspection or testing has been carried out too!

 

[terryshand]

It looks like all the cables are 2 core with a bare earth or 3core with a bare earth except 1 which looks like a 3core flex. Most of the bare earths are not used.
I cant see the wires in the ceiling switch as they are too short and wont allow me to pull it down far enough, its just occured to me other ceiling switch has been replaced with a new wall switch & has L1 brown, L2 black COM grey.
Its getting dark so this must go on hold till tommorrow as I only have a stupid little torch.
Thanks for your help guys its been terrific so far

 

[electronicsuk]

My 10p is on that one of the twin and earths is a switch wire and is connected across L&N, but all those wires at one point is a nightmare!
You need to start by identifying which cable goes to what. Is there access from above in a loft?

Yup. Mind you, doesn't explain why it takes out "both trips", which presumably means two MCBs.