Upstairs lights keep tripping

[dmcg14]

When i got up yesterday morning i noticed the upstairs lights had tripped. I put the breaker back on and after half an hour or so they tripped again.

As a total coincidence i was planning on changing all the ceiling rose's as the excisting ones are old, so seen this as a good opportunity to change them and hopefully fix the fault at the same time.

I disconnected the front bedroom light, then had to stop due to poor light. At this point the front bedroom light was disconnected. The back bedroom and cupboard were untouched and the top landing was still connected but the ceiling rose had been unscrewed. I switched the breaker on and the top landing light didnt work, the cupboard flickered, and the back bedroom worked fine. They then tripped after a period of time so i left them off overnight.

This morning i disconnected all 4 lights and fitted new ceiling rose's but now when i try to put the breaker on, the rcd trips. I tried changing the breaker but had the same issue. I have then disconnected each light in turn and tried to put the breaker on at each interval but the rcd still trips. Now with every light disconnected the RCD still trips. Any ideas?

 

[Aragorn84]

Is it specifically the MCB for the upstairs lighting thats tripping, or the RCD for the whole board/section of board?

Your post is confusing as you say the RCD trips but then mention putting the breaker for that specific circuit back on.

 

[dmcg14]

Its a split-load CU so an RCD protects the upstair lights, kitchen sockets and central heating. The upstair lights breaker had tripped. Now when i try to put the breaker back on, it forces the RCD to trip. Does that explain better?

Thanks

 

[wingcoax]

You obviously have a (few) wires in the wrong terminal(s). Did you make a note of which went where?

 

[dmcg14]

Yeah i took a note of which went where:

Front bedroom
- 1 white core in red sleeving connected to the blue core of ceiling rose
- 2 black cores in black sleeving connected to the brown core of ceiling rose
- 2 earths connected in the earthing terminal

Back bedroom
- same as front bedroom

Top Hall
- 1 white core in red sleeving connected to the brown core of ceiling rose
- 1 black core in black sleeving connected to the blue core of ceiling rose
- 2 earths connected in the earthing terminal

Does that sound right?

 

[ban-all-sheds]

White cores?

What type of cables are these? How have you got (probably) 1 live, 2 neutrals and 2 earths at the bedroom lights?

What's at the switches?

If you disconnect everything do you still get the MCB or RCD tripping?

Do you have a multimeter?

 

[dmcg14]

At the front bedroom switch i have 1 red core in common and one white core in L1. At the back bedroom switch i have 2 red cores in common and 1 white core in L1.

So from this i assume the white cores are my switch wires, the red cores which aren't visible at the ceiling rose, are my loop and connected elsewhere, and the 2 neutrals and 2 earths are 1 from the supply and 1 going to my next light?

 

[dmcg14]

When the front bedroom and top hall are completely disconnected, and the back bedroom the ceiling rose cord disconnected, the MCB still trips the RCD.

I dont have a multimeter at hand but could get one for tomorrow.

Thanks

 

[ban-all-sheds]

At the front bedroom switch i have 1 red core in common and one white core in L1. At the back bedroom switch i have 2 red cores in common and 1 white core in L1.

Are these all single-core cables?

Are they insulated and sheathed?

Are they run in steel conduit?

So from this i assume the white cores are my switch wires, the red cores which aren't visible at the ceiling rose, are my loop and connected elsewhere, and the 2 neutrals and 2 earths are 1 from the supply and 1 going to my next light?

Sounds reasonable.

But no earths at the switches?

When the front bedroom and top hall are completely disconnected, and the back bedroom the ceiling rose cord disconnected, the MCB still trips the RCD.

Given that, and the problems of random tripping and flickering lights you describe, I'd say you have a fault somewhere else, it could be a conductor which has come loose, or it could be a damaged cable.

I dont have a multimeter at hand but could get one for tomorrow.

You might be better off getting an electrician....

 

[dmcg14]

Are these all single-core cables?

Are they insulated and sheathed?

Are they run in steel conduit?

They are run in steel conduit, they are all single core cables as far as i can see at the switches. They are insulated, hence red and white cores, and they are not sheathed.

But no earths at the switches?

There are 2 earths at each switch connected to the back box

Given that, and the problems of random tripping and flickering lights you describe, I'd say you have a fault somewhere else, it could be a conductor which has come loose, or it could be a damaged cable.

I dont understand how a conducter can become loose given that they have been working for a long period of time, and also dont understand how a cable can become damaged since they are run in conduit.

You might be better off getting an electrician....

I have a degree in electronics, an HNC in electrical engineering and i'm employed as an electrical engineer, so i think i'm more than capable/qualified to be tackling a lighting circuit. The only problem i have is i have little experience working in houses, hence the reason i ask for advice on here

 

[dmcg14]

Since my last post i have disconnected the main neutral in the CU to ensure the RCD isn't faulty. With the main neutral disconnected, the RCD still trips so this would say the RCD is fine, but i probably have a neutral fault somewhere I then started to disconnect every neutral in turn, then every earth, then every switch wire, so at present no wires are connected at any fitting on the circuit.

Any suggestions where i go from here?

 

[wingcoax]

At this stage in the game all you can do is check each wire against all the others for shorting to each other and the conduit. Hopefully you will find a fault.

 

[ban-all-sheds]

I dont understand how a conducter can become loose given that they have been working for a long period of time, and also dont understand how a cable can become damaged since they are run in conduit.

So once something is working it never breaks?

When i got up yesterday morning i noticed the upstairs lights had tripped. I put the breaker back on and after half an hour or so they tripped again.

That was before you had done anything.

Something had gone wrong all on its own...

I have a degree in electronics, an HNC in electrical engineering and i'm employed as an electrical engineer, so i think i'm more than capable/qualified to be tackling a lighting circuit.

Get hold of an insulation resistance tester and start checking each segment of the circuit.

 

[sparkwright]

Front bedroom
- 1 white core in red sleeving connected to the blue core of ceiling rose
- 2 black cores in black sleeving connected to the brown core of ceiling rose
- 2 earths connected in the earthing terminal

Back bedroom
- same as front bedroom

It would seem you've got the white core going to the neutral of the lampholder, and the blacks going to the live of the lampholder.

White is switched live,
and the blacks should be the neutral.

This shouldn't cause the RCD to trip though.

Make sure there are no wires shorting together, or against any metalwork like the conduit/fixing screws.

 

[sparkwright]

Have you worked on or disturbed any switches?

Any lights etc outside getting wet inside?