Tripping Light Circuit

[CER]

I've had a new shed/garage built. New electrics were installed by an electrician, and were we all working ok. Perhaps now a mistake, i did not get the electrician do a first and second fix, I got them to do the job in one go, knowing that I would then install plasterboarded out one of the rooms. When plasterboarding out I detached from the wall the supply fuse box and slid plasterboard behind, but no wires were disconnected in doing this. However L1 & L2 as per the diagram weren't quite in the right place so I moved them. There was enough slack in L1 to move it, however I used a junction box and extra piece of wire to move the position of L2.

However now when I turn on the light circuit the RCD trips in both garage and main unit in the house. (after reading one other posts it mentioned that having RCD in series might not be normal???)

First of all I removed L2 from the circuit, then I removed S1 and L1 from the circuit, so that L1 is just acting as a junction box towards S2, and the circuit is still tripping. Luckily I can still access the wires by removing some of the exterior boarding, and have checked for damage to cables by screws, but can't find any. (can only visually see 80%) but all moving about ok.

Therefore i think I have removed as much as I can from the circuit in terms of changes made, but its still tripping. Have called electrician who installed it, but he's not available for 3 weeks. So posing here to see if there are any suggestions.

A few searches suggest a 'leak to earth' might be an issue, but I don't have any equipment that can test, unless any suggestions?

The picture of the light box is L1, and shows switched live cable disconnected, but L2 disconnected cable is out of shot.

Any suggestions of help greatly appreciated.

Thanks.

 

[EFLImpudence]

First of all - what is tripping? MCB(NSB things) or RCD?

Secondly - when is it tripping? As soon as you switch on or after a while.

Have you screwed through a cable?

 

[EFLImpudence]

I see you said RCD was tripping.

You do have two L1s and L2s which is confusing.

 

[CER]

The RCD in both the garage and main unit trips every time. So if I turn S2 off, and reset the RCD's, then when I turn S2 on, it trips both RCD's. If I leave S2 on then its not possible to reset both RCD's as they trip each other.

I did think it might be a screw, I've already had a good look and can't see anything obvious.

 

[CER]

sorry yeah just noticed diagram is a bit confusing. See update to original post.

 

[EFLImpudence]

It could be as simple as a blown bulb - especially if you're using filament ones.
Take out the bulbs and see what happens.

If not you must have made a mistake rewiring or a screw through the cable.



Both or either RCD will trip, they see the same fault.

 

[CER]

Have checked all the bulbs (L3,4,5, as per the updated diagram) but non are blown. When the switch is turned on for the circuit I see a flash of light in the bulbs before the rcd trips, but the bulbs arn;t blowing.

Therefore, as i have removed S1, L2 and L1 from the circuit, the extent of the changes I have now made in terms of wiring is the picture of the light fitting L1 (12.jpg) which I was trying to show is now simply a connection box between the supply and S2. I'm pretty sure its right.

I've triple checked the wire and can't see any damage.

 

[winston1]

I would first check the wiring in your new junction box. After all that is all that's been touched.

But to be honest the electrician has done it all wrong. An RCD and 32 amp MCB in the house feeding another RCD and 32amp MCB feeding sockets in the shed! So a socket overload in the shed will trip both 32 amp MCBs or an earth leak in the shed will trip both RCDs (as you have found out).

If you retain the shed RCD the house MCB should be moved to the non RCD side of the board.

For proper discrimination the house MCB should be higher than the shed one, maybe 40 amp if the cable is suitable, or the shed one reduced to20 amp.

All the advantages of a separate light circuit in the shed are lost if the house MCB trips.

I guess you didn't need the shed CU at all, the sockets could have been run direct and the lights through switched FCUs.

 

[securespark]

Have you screwed through a cable when fitting the pendants?

If you have disconnected all the lights in the room with the supply and it is OK, ie not tripping and all the lights in the adjacent room are working, then there must be an issue with the wiring to L1, L2 & S1.

Use a multimeter on the ends of the wires feeding these fittings (with lamps out and power off) to see if there is a short.

 

[CER]

I can't see any damage the cable, I'm actually able to get see and see into void to see the wires.

I have disconnected everything in the room with the supply (except the 'pass through' to the other room), however despite not making any changes in the other room the rcd still trips.

However, the symptoms have now changed slightly, after attempting to do some fault finding, the rcd in the shed now trips after about 5 secs of having turned it on, even if the two circuits connected to it are turned off.

 

[EFLImpudence]

It's obviously not possible to detect earth leakage from here, so

if you cannot test the wiring for earth leakage, then the only thing to do is start again and rewire it bit by bit until it trips.

I don't know your experience but am concerned that the two different methods of switching apparent by your diagram may have lead you to make a mistake.

In the picture of the ceiling rose, there is a blue wire with a brown sleeve. What is that?

 

[CER]

The blue wire with the brown sleeve is the switched live from S1. Therefore at present the S1 is not connected.

Guess i'll just have to wait until I can get an electrician out.

Any other suggestions welcome, but I will close out the thread once I get it sorted.

 

[Risteard]

For proper discrimination the house MCB should be higher than the shed one, maybe 40 amp if the cable is suitable, or the shed one reduced to20 amp.

Wrong. For full discrimination two circuit breakers to BS EN 60898 in series will never be suitable.

 

[Spark123]

Does that not depend on fault levels?

 

[Risteard]

Does that not depend on fault levels?

Not really. If we are talking about fault protection as opposed to overload protection then there is liable to be sufficient current to operate any and all devices in most cases.

Fuses or MCCBs are far better for achieving selectivity (discrimination).