Single light tripping RCD for some reason

[Gethin]

Hello,

I renewed the wiring for the lights up in the attic; I moved the light switch from the attic to the cupboard and put a new three gang light switch. It’s basically rear outside lights, Attic lights and cupboard light where the RCD is located. Originally the light switch was wired up to a ceiling rose. All I have done is changed the ceiling rose for a 20A junction box with three rows of block connectors which makes 12 connections. All I have done it connected everything the same as you would in a ceiling rose connection, Switch Live is connected the same way as well. Press the light switch and the light on in the attic which is a bonus, but when you turn off it causes a short and trips the RCD. I am left scratching my head because it should work perfectly. If it tripped the lighting circuit I would understand it’s the lights causing the problem. But it’s tripping the RCD for that side of the fuse board. I should point out that I have a dual RCD fuse board it has three RCD’s the main one for the entire fuse board and the fuse board is split into two sections. The one where the lights are connected including a ring main trips when your turn the switch off. I didn’t do this before I changed it over to a junction box. If I had a Mega Meter I could find out what is causing the short, I’ve tested the circuit does open and close but I am not certain what is causing this to short out.

…Oh, all the switches are wired independently, the attic, cupboard and outside lights. The other witches for the cupboard light and the outside lights are fine it’s just that one switch for the attic lights. I was wondering if the 3 gang light switch is faulty… which something I haven’t tested yet is, I shall rewire the switch for the outside light and cupboard and see if this still happens. If it does then, I know it’s a fault with the switch. The original wiring was done when we purchased the house 17 years ago; it was all rewired by an approved electrician. Although, he wired the attic lights to a ceiling rose instead of a junction box for some reason. Maybe it was because it made it easier. I used a 20A because there are three cables and one switch live return.

Any thoughts on this problem would be gratefully appreciated because I’m out of options.

Thanks,
G

 

[ban-all-sheds]

All I have done is changed the ceiling rose for a 20A junction box with three rows of block connectors

You need a 4-way JB to replace a ceiling rose.

All I have done it connected everything the same as you would in a ceiling rose connection

In a ceiling rose you have

1. permanent live
2. switched live
3. neutral
4. earth

In your JB You have 3 sets of terminals.
How did you connect everything up?

And were all the lights on the same circuit beforehand? The outside lights weren't spurred off a socket circuit?

If I had a Mega Meter I could find out what is causing the short

How?

 

[EFLImpudence]

Although, he wired the attic lights to a ceiling rose instead of a junction box for some reason.

That way removes the need for an unnecessary junction box.

 

[Gethin]

I BOS, (sorry I abbreviated your name)
I think I might know where I have gone wrong and the cause of the short; although if I try to paint a picture where you can see what I have done may make some sense. The 20A light JB has three connector blocks one in the centre and two either side. I have divided the three into sections, one for the loop and another for neutral and then switch live return. The earth cables I have connected into a single 5A connector block.

So basically it’s similar to a ceiling rose. I apologise if I'm sounding confusing.

All L cables to a Loop (apart from SW/L)
All N to Neutral
All E to 5A connector block

I think I'll pit it back to a ceiling rose which is the way it was before... I'll get a new one because the other one was a little tatting, I know it's up in the attic and not on display but a new one would be better. I think the sperate connection blocks is causing a short for some reason, place this all back into a rose and it will stop. Although, I still don't understand why. logically it shouldn't make any difference because it is wired the same N to Neutral and L to Lopp and SW/L... it shouldn't make a difference but it is causing a short. I was thinking it could be because there are too many connections on each block, there are 4 not being used and I was wondering if this was causing the short light an open circuit. I screwed them down to make sure it didn't cause a short but it did. Ill change it back.

Thanks guys for your help.

 

[EFLImpudence]

Press the light switch and the light on in the attic which is a bonus, but when you turn off it causes a short and trips the RCD.

How many wires are in the switch?

I am left scratching my head because it should work perfectly. If it tripped the lighting circuit I would understand it’s the lights causing the problem. But it’s tripping the RCD for that side of the fuse board.

It would wouldn't it?
Following your logic, the RCDs would never trip.

I should point out that I have a dual RCD fuse board it has three RCD’s the main one for the entire fuse board

Are you sure one is not just a switch? You should not have three in a 'dual' board.

and the fuse board is split into two sections. The one where the lights are connected including a ring main trips when your turn the switch off.

It sounds like you have a wire in the 'other' terminal of a two-way switch which you should not.

I didn’t do this before I changed it over to a junction box. If I had a Mega Meter I could find out what is causing the short, I’ve tested the circuit does open and close but I am not certain what is causing this to short out.

It doesn't seem like an actual fault. You have done something wrong.
Start again.

 

[ban-all-sheds]

The earth cables I have connected into a single 5A connector block.

Which provides the function of the 4th terminal you would have had in the right sort of JB.

I think the sperate connection blocks is causing a short for some reason,

Not possible.

And anyway - a L/N short would not trip an RCD, it would take out the MCB.

place this all back into a rose and it will stop.

It won't.

Although, I still don't understand why.

That's because there is no reason.

logically it shouldn't make any difference because it is wired the same N to Neutral and L to Lopp and SW/L...

Exactly.

it shouldn't make a difference but it is causing a short.

If you have a short then:

1) It's because of your workmanship, not because of the nature of a JB.

2) It would be tripping an MCB, not an RCD.

I was thinking it could be because there are too many connections on each block, there are 4 not being used

Sorry, but if you thought that it shows you have a really flaky grasp of how things work.

and I was wondering if this was causing the short light an open circuit. I screwed them down to make sure it didn't cause a short but it did. Ill change it back.

If you've got an RCD tripping it will not be because you've moved L&N conductors from a rose to a JB.

You've done something else wrong, so moving them back won't fix anything.

I moved the light switch from the attic to the cupboard and put a new three gang light switch

What switches did you have before, and what did you do with the cables that were connected to them?