MCB switch trips when all lights are switched off

[AJonesyA]

Hi,

I don't know how simple this is to solve and I apologise for any simple language that I may use as I'm not an electrician.

As you can see from the title of the post the mcb switch trips when all the lights in our bungalow are off.

This has literally only started to happen this week and I know it is my fault and yes I shouldn't mess with things I don't understand.

What I have done is remove 2 fluorescent lights and one old plastic spotlight from our old kitchen. I was careful not to mix up wires etc.. as I understand that these lights are on a loop. I am now left with the following:-

1. A small hole in the ceiling with 3 grey wires each one with a live, neutral and earth.

2. Another small hole in the ceiling with 2 grey wires each one with a live, neutral and earth.

and

3. Another small hole in the ceiling with 1 grey wire with a live, neutral and earth.

What I want to do it get rid of the 3 and 2 grey wires. I have put a basic pendant fitting on the hole with the one grey wire and that seems to work okay.

I take it that by messing with these wires I have caused something to start tripping?

My questions are:-

1. Why would it happen when the lights are off?

2. How should the grey wires i.e. the 3 together and the 2 together be joined i.e should all the lives be joined in a block, all the neutrals together and all the earths together?

3. I take it that as it is a loop you cant just cut the wires and tape them?

4. How can I solve this and how do I actually find the fault?

Thank you in advance for any help that I get.

Andy

 

[ricicle]

How did the lights switch before ?

 

[Chri5]

Are you ABSOLUTELY sure all the lighting was on the same circuit ?

Say the wall lighting was via a ring (and fused spur), and you have now added that in to the lighting loop- If they were on different rcd's you'd have a shared neutral with would cause a trip.

Might be a good idea to isolate the lighting circuit at the board and then test all the wires, if any are live then you would appear to have been using 2 x circuit to control seperate areas of the lighting.

On standard rose you would (not always, but mostly) expect a cable in live, loop out to next light AND a wire down to the switch.

Have a look at the Wiki on the tabs at the top of the page, UK electrics- lighting.
Those wiring diagrams may help resolve your issues.

 

[bernardgreen]

1. Why would it happen when the lights are off?

2. How should the grey wires i.e. the 3 together and the 2 together be joined i.e should all the lives be joined in a block, all the neutrals together and all the earths together?

The grey are cables and each has 3 wires in it.

One is bringing power to the rose, one is taking power forward onto the next rose. These should have their red and blacks joined red to red and black to black. Earth to earth.

The third cable goes to the switch where red and black are joined together when the switch is on. By connecting the red in that cable and the black in that cable to the red and black in the other cables you are shorting the live and neutral via the switch. Hence the trip tripping.

 

[AJonesyA]

Firstly, thank you all for answering so quickly. I think I am going to have to get the electrician in but before I do I just had a couple of things I wanted to say/ask to to see if it would solve the problem.

I have been round all the light switches in the house and removed them just to check the wiring in each one is okay and it is, good start.

The third cable goes to the switch where red and black are joined together when the switch is on. By connecting the red in that cable and the black in that cable to the red and black in the other cables you are shorting the live and neutral via the switch. Hence the trip tripping.

Sorry if this is a silly question but if I was to disconnect all the wires from each other so I basically end up with 3 live, 3 neutral and 3 earth but not touching each other would that stop the tripping? I dont actually require these lights anymore and as it is in an old extension I think they are on their own loop.

Or

Is there a better, easier and SAFER way to isolate the wires.

This is my last shot and then I will get a guy in I know.

Cheers
Andy

 

[Chri5]

Sorry if this is a silly question but if I was to disconnect all the wires from each other so I basically end up with 3 live, 3 neutral and 3 earth but not touching each other would that stop the tripping? I dont actually require these lights anymore and as it is in an old extension I think they are on their own loop.

Or

Is there a better, easier and SAFER way to isolate the wires.

This is my last shot and then I will get a guy in I know.

Cheers
Andy

As already mentioned it would be likely that you have 3 cables at a rose, in, out and switch.

You need to find the switch wires and remove them, this would retain the live loop which may include lights you need to use.

If you are happy that the total circuit isn't required then disconnect the LNE wires inside the CU and remove the cable. Unless you have a fuse blank, leave the fuse / mcb in and marked the CU position as spare.

Bernards likely have told you the reason for the fault, if you have a multi meter.....

Join the redundant LN switch wires at the switch, then at the ceiling rose (having turned off the power) test for continuity. The wire that has continuity will be the wire down to the switch. Once these switch wire(s) are disconnected from the loop wires the fault will clear.

 

[securespark]

Is the MCB tripping immediately you switch it on?

If all you have touched is the three fittings, isolate the supply, then disconnect the wires from each other and fit a terminal block to each. Reconnect the supply.

Does this stop the tripping?

 

[AJonesyA]

Hi,

Yes the MCB trips the instant I turn it on.

I have done as suggested and now separated all wires and out them in blocks.

Unfortunately it still trips.

I think I may have to give up as I am clearly missing something and not capable of doing this

If anyone does have final ideas that would be great but if not I would justlike to thank you all for responding and your help.

 

[AJonesyA]

Actually Ive just had a thought, sorry if its a stupid question.

If all I have done is remove 3 light fittings and have now isolated each wire separately is there any reason it would still trip from just doing that or could it just be coincidence? i.e what are the chances it could be a faulty MCB switch? or do they rarely fail?

Arrgghh!! this is taking over my brain.