Help needed again pls - Lighting fault tracing

[AJB Temple]

I need your help please once again in tracing a fault. Am DIY but not clueless. Converting former kitchen into 2 rooms: bathroom and laundry. The room had 24 cheapo ceiling spots, originally tungsten then 240v GU10 LEDs that I am replacing. Circuit spilt into two halves with two gang wall switch controlling (this will be in the laundry side). There is also a redundant smoke detector wired in to the same circuit.

I pulled down the spots in what will be bathroom in order to repair ceiling, knowing I will be replacing with good quality IP65 (astro). This should not be notifiable work as it is just replacement of existing with upgraded fittings. Taking the spots down (not brutally!) has caused the lights operated from one side of the two gang switch to trip the MCB with a flash. Neutrals are present in switch box and all joined together (unused) as expected.

MCB does not trip if I remove the wires from the switch on what will be the bathroom side, so the laundry side has no fault and MCB must be OK, but pops instantly if the other circuit is put back in. RCD does not trip at all in Hager CU (which happens to be in the laundry room).

Can’t get access to the floor above the joists, and it’s difficult to see visually how the spots have been wired as they span several joists. All spots on the bathroom side have now been removed and temp wagos fitted. BTW I'm removing some of the lights permanently as well. They are definitely not daisy chained and from gentle tugging I would guess there are at least two junction boxes up there somewhere and one of the light fittings was also used as a mains junction by the look of it as there are two white flex T&E ends going to this fitting point. I expect one junction box must be near where the smoke detector was fitted.

Not had chance to do any tests yet, but would appreciate some pointers as to what to look for that would cause the instant trip and flash of the MCB. It's presumably a short circuit somewhere as I can’t see any faults at the spots, nor any evidence of overheating at the spot terminations. I have suitable Megger MFT.

When I find the fault and fix it, the plan is to replace the switch with a 2 gang Quinetic with built in receiver, so that I can pair the bathroom side with wireless switches in bathroom and bedroom, as it is no use having the bathroom switch in the laundry room.

Thanks, AJ

 

[westward10]

I presume you were removing these lights without the power isolated.

 

[timhoward]

Normally neutrals all joined at switch suggests power to the switch, and then from there to the lights, with the N's all joined together.

Instead of repeatedly tripping the MCB I'd turn the power off, then label, separate and safely terminate the switch wiring.
I'd then test what I suspect to be the feed to the faulty lights from the switch. Assuming a fault will show itself, I'd then check terminations on every light. If the issue is found, great. Otherwise you are into trying to find and pull joint boxes through downlight holes or finding a way to isolate the faulty section and rewiring the lighting.

(Ultimately if you can find the cable from the switch or a different permanent-live cable, and find fault-free cables spanning the joists, then you can very likely replace the wiring for the remainder. )

 

[AJB Temple]

I presume you were removing these lights without the power isolated.

No. Power fully isolated and dead tested using Megger TPT 420 (not the MFT). I intended to keep using the lights for the time being as it is a working area and it protects the new ones. Lights just pulled down to release the clips from the ceiling. This triggered the fault when I tried to switch the lights on again. So I then went on to remove the lights fully with circuit again dead tested.

 

[westward10]

Sounds like something has shorted out when you took the lights down this could easily be the joint boxes you were pulling on.

 

[AJB Temple]

Thanks Tim. That's really helpful. I always habitually safely terminate everything with wagos anyway as soon as I disconnect and I have done that in the switch box and at the wires in the ceiling. I think I confused myself a bit as there seems to be T&E that is not from the lighting switch into the ceiling, as the former smoke detector is up there and at least one of the lights appears to be wired in to that JB. If I can find where the supply comes in to the ceiling I may just follow the suggestion of rewiring the whole lot, as I could get into the ceiling from underneath enough to bridge the joists, without creating too much repair work.

I have spare MCBs in the CU so at a push I can just put a complete new circuit in though would prefer not to as it is very awkward due to structural beams.

 

[AJB Temple]

Sounds like something has shorted out when you took the lights down this could easily be the joint boxes you were pulling on.

Thanks. Yes, that is what I figured. If only I knew where the JBs are!

 

[SJD]

Thanks. Yes, that is what I figured. If only I knew where the JBs are!

So was this room originally wired with 2 light fittings, one on each switch, then converted at some point to downlights? If so, the junction boxes typically might be close to the orginal 2 lighting points. You can often see evidence of old lights in the plasterwork, assuming the ceiling was not skimmed at the time.

 

[AJB Temple]

So was this room originally wired with 2 light fittings, one on each switch, then converted at some point to downlights? If so, the junction boxes typically might be close to the orginal 2 lighting points. You can often see evidence of old lights in the plasterwork, assuming the ceiling was not skimmed at the time.

Hmm. Don't think so. It was a barn conversion back in the 80's (long before we bought it) and although I can see evidence of the old kitchen layout being altered / refurbed I can't see any evidence of a ceiling rose point, especially on the laundry side. However, you do make a good point as there was at one time a pulley light fitting over a table and that is on the same segment between joists as the smoke detector.

The last owners did a lot of DIY electrical quackery with great aptitude. They showed amazing expertise at twisting wires together to form a connection and protecting them with insulation tape. It was not necessary to attach CPCs to metal boxes, and on some sockets it was perfectly OK just to shove wires in without expending unnecessary effort tightening up screws. Orange cable used for garden tools can in fact be used anywhere in house wiring apparently.

 

[timhoward]

I think I confused myself a bit as there seems to be T&E that is not from the lighting switch into the ceiling, as the former smoke detector is up there and at least one of the lights appears to be wired in to that JB.

The smoke detector is actually a clue as that will have a permanent (unswitched) supply.
If a light is wired into the same joint box as the former smoke detector then an assumption can be made that there's both permanent and switched lives within the box.

 

[AJB Temple]

The smoke detector is actually a clue as that will have a permanent (unswitched) supply.
If a light is wired into the same joint box as the former smoke detector then as assumption can me made that there's both permanent and switched lives within the box.

Thanks Tim. I will start there by taking a piece of ceiling out to see if I can locate a JB. The cable to the old detector does not move much and my guess is JB is probably very close. I've got to get wires across the joists anyway as there are three spots currently on the wrong circuit.

 

[westward10]

Downlights can be a minefield of bad wiring and if it were me I would want the lot out even if it means taking the ceiling down.

 

[littlespark]

If mcb tripped with a bang, then something somewhere will be visually blackened….. and quite possibly melted beyond being now connected to the terminal.

As stated, downlights can be a minefield to work on… especially ones put in by less than competent individuals who just cut off cpcs and leave taped up live connectors in the ceiling without an enclosure.

Worst case scenario would be of the downlights were wired and connected from above with the floor up, and now there’s not enough spare on the cables to pull them down

 

[AJB Temple]

There was enough cable slack to remove all of the down lights without a problem. Four of them were connected to an opposite downlight within the same adjacent spaces between joists and those wires were easily pulled out without a problem and the ceiling holes repaired. By far the tightest cable was the one to the former smoke detector and my expectation is that the JB near where this is will be the root of the problem. I can't get to it easily at the moment as I have a big track saw sheet cutting bench underneath, but plan to get in there tomorrow by cutting a square of ceiling out between joists.

I may well bite the bullet and run new cable throughout that room. I wont need to take the ceiling down. If necessary we will ditch the entire lighting circuit at the CU end and run in a new one. Luckily it only services one room with two circuits running into the same MCB.

As surmised above, whoever installed this mostly used round rubberised T&E and just snipped all the CPCs off. There is no evidence of any blackening at any of the lamp ends (nor on any of the removed light fittings) but a JB terminal somewhere will be toast I expect. I will test everywhere for live and end to end continuity when I can get proper access with the bench out.

The new lights all have proper JBs so I may as well do a proper job of the wires as well.

 

[westward10]

What joint boxes are you using?

 

[AJB Temple]

I meant that each new light fitting has a daisy chain joint box as part of the light fitting. The light fittings are astro mimima IP65 deep set units that take GU10s above a glass screen and dust seal. I don't actually need IP65 everywhere as it is a large room and most lights are not in a high exposure zone, but we decided to use them anyway. Any other junction boxes in the sealing void will be wago, with wago 221 connectors.

 

[davesparks]

Just have the ceiling down and start again with it.

You know there's poor wiring and electrical problems up there so just have the lot out and put it right.

There's no point doing all that work to make 2 new rooms and leaving a fire risk in there for the sake of a few sheets of plasterboard.

 

[AJB Temple]

That is a single trade approach. To do so adds about £1,000 of cost and 8 weeks to a refurb that my wife expects to be finished pronto. I have to make good my own mess. One problem is that round here plasterers are booked ages in advance. I am a hopeless plasterer, especially on ceilings. However, I will be able to trace the live feed and all of the junction boxes even if I have to hire an inspection endoscope. Might take a couple of days.

 

[westward10]

No it is the wise approach and I suggested this earlier but it is your house to burn down if hidden issues remain undetected.

 

[AJB Temple]

With respect, and thanks for the help, I don't see the logic of this. Here's why: There are two wires coming from a single MCB at the CU which is 7 or 8 metres away at its furthest point. These two wires feed only the two lighting circuits in this single room. I can readily identify L, N and CPC for both cables at the CU and disconnect them permanently from the CU. The wires are loosely laid between the joists, in air voids with no insulation. I have a degree of access to these voids through the light fitting holes. With a camera if necessary this should enable me to identify where the wires run, where any junction boxes are, and if necessary cut small, repairable, holes in the ceiling from below to remove them. Disconnecting from the CU should remove any fire risk, but even if it didn't removing the wires surely would. All that removing the ceiling does is surely to provide easier access for removing the wires, but with a lot of mess and delay.

If there is something I am missing, please tell me and I will see how I can deal with any risks. Thanks for the thought provoking input. It is helpful.

 

[westward10]

Removing the ceiling exposes all risks. You state you are no plasterer so you would not attempt this, you are clearly no electrician however you are happy to peruse this and I'm sure Confucius would have a opinion on this. A poorly finished ceiling poses little risk, poor electrical installations pose a significant risk to life. Plastering requires a great deal of skill with a modicum of knowledge, electrical works require a great deal of both, think on it.

 

[AJB Temple]

Thank you. That doesn't answer my question though. A camera accessing the ceiling also exposes all risks. Removing the wires via existing holes also removes all risks. What is the logic for demolishing the ceiling if wires can be stripped out without that?

 

[timhoward]

Thank you. That doesn't answer my question though. A camera accessing the ceiling also exposes all risks. Removing the wires via existing holes also removes all risks. What is the logic for demolishing the ceiling if wires can be stripped out without that?

If there is nothing dangerous upstream of where you tap into the circuit, and no other wiring/circuits with previous DIY efforts then you might get away with it.
You have rather eloquently described this house as an electrical disaster waiting to happen, hence the comments that this is a chance to make sure this area is ok that should be seized.
Ceiling board isn’t expensive, and if you are converting into two rooms won’t there be a plasterer on site anyway at some point?

 

[AJB Temple]

Thank you Tim. We have had the house for nearly 9 years and said in previous threads (I had one fault fining recently in room connected to this on) that we have worked our way through. Much of it is new and finished and was professionally rewired (where it was not new), though the electrician who did this has moved to Eire recently. The old kitchen was the last room to do because it has been a workshop for the past year or so. One of the refurb jobs has been to remove all sockets from this area as it becomes a bathroom. The laundry room has a new 13 amp radial direct to secondary CU in this case with AFDD. That room is finished apart from some shelving and decorating (in progress). No plastering is done or planned because internal stud walls and 200mm of extra insulation have been added throughout the old part of the property, with membrane and panelled insulated walls over that. This has obviously made rewiring a great deal easier. The new bathroom is fully insulated and has cement board walls against membraned insulated stud for full tiling. Hence no need for plastering. I do the tiling.

I agree that ceiling board is cheap and I have installed plenty. However, the excellent plasterer we trust and have used in the past for the new build parts is booked until July /August as we are in an area where they are putting in very large numbers (thousands) of new build. Reliable trades are in short supply - same applies to brickies for instance.

I will inspect the void today, having relocated the track saw bench.

 

[AJB Temple]

SOLVED
Thanks for all the help. It was nothing to do with the smoke detector. In this new hole (where there will be a light fitting) three white T&E wires were fed from this "junction" (see pic if it loads). One supplied the redundant smoke detector and the other two run round the lights in two different directions with a further radial connection at another light point.

There was no junction box at all. CPC connections made by uncovered twisting, and everything else crammed into a strip connector, where there was a short and a bit of blackening (hard to see in the photo). I've traced point to point and there are no other junctions that are not at a former light fitting point. The old wires have then been used to pull through new wires in the whole room and back to the CU. (The pull through proves there are no other junctions). The switch segment buried in the wall (quite short) has been removed as it will be replaced by a quinetic controller anyway. A new wire has been run from an unused lighting rated spare MCB for now (CU will be replaced with another all RCBO and possibly AFDD set up when an extension is built). So this cable feeds only the bathroom lights and nothing else (apart from the controller).

I think this lot may be the original wiring from the developer when the house was first converted and is pretty much the last remnant left in the building. What I thought was a mains fed smoke detector in the laundry area, was in fact a dummy and not actually connected to anything at all. Amazing. The one in the new bathroom was fine. It's hard for a layman to understand how developers and employed trades can do this kind of work, with poor terminations and no junction boxes.