Baffling electrical fault... Any hints very welcome.

[ASteve]

Hi... I'm hoping that there is something obvious I am overlooking... but I can't imagine what it is. Any hints or tips would be very welcome.

My house was built in the late 1970s. Around 2012, a conservatory with a double skinned wall approx 18" tall was built. I bought the house in 2018. In the conservatory wall there are 4 double sockets, and a fused switch. A fan and light hang from the middle of the conservatory - this has a remote control and is isolated by the fused switch.

Everything has worked for about 7 years... then, recently, I noticed that both the sockets and light in the conservatory had stopped working at around the same time. I investigated my RCU - expecting that something had tripped... but nothing had. All the switches were in the "on" position - indicating no problem with earth-leakage on any of the circuits in my house.

While my memory, of the time when the sockets in the conservatory worked, might not be perfect... I think I remember that the conservatory circuit was part of the upstairs circuit - despite being ground-floor. Nothing on the RCU is labelled 'conservatory"... and everything except the conservatory electrics work perfectly. This suggests, to me, that my RCU and all modules are working properly... so, whatever is wrong with the conservatory electrics, I'm fairly sure it is not leaking to earth and isn't a short circuit... as both of these should have caused one circuit, at least, to have tripped at the RCU.

I've lifted my upstairs floorboards in the rooms in the house above the conservatory - but have not discovered any wiring going to the conservatory between the downstairs ceiling and the upstairs floor.

I got a multimeter and a tone-trace tool... and I've tried to use these to work out where the wiring is routed... and I've ended up very confused. The fuse in the switch is a 13A one - and is not blown... and the electrics in the conservatory don't work whether the switch is in the on or off positions.

Layout: If I imagine a clock face on my conservatory floor... I can walk into my conservatory at 6-o'clock through a wide doorway from the house. At 3 o-clock there are patio doors. Except where there are doorways, there's a low double-skinned wall - with the UPVC conservatory on top. The floor of the conservatory seems to be concrete - and there are ceramic floor tiles covering it. These can't be removed without replacing the entire floor. The floor in the house is also concrete. I don't think there’s any electrical cables buried in concrete floors - either in the conservatory or the house. On top of the low conservatory wall, there are windowsills - I can't see any way to remove them without demolishing the conservatory. The fused switch is at 4 o'clock... and there's a double socket at 5 o'clock both in the low conservatory wall. There are also double sockets (on the other side of the external conservatory door) at 9, 11 and 1 o'clock.

With the power to the entire house off, I unscrewed the fused switch at 4 o'clock - and the double socket at 5 o'clock... in the low wall between the house itself and the conservatory external door at 3 o'clock. There are two similarly heavy gauge twin-and-earth cables entering the back of the back-box through a grommet. The back boxes are sunk into the inner skin of the low conservatory wall, for the sockets and switch. This conservatory wall is not plastered - so there's no way to hide cables that way... they must run in the cavity between the inner and outer walls. The cables are not visible. The fused switch at 4 o'clock has one larger and one smaller twin-and-earth cable. I think the thicker cable at the switch puts live/neutral in common with live-neutral on the socket next to it. I think I've traced the thinner cable (using the tone-generator) along the low wall (towards the house) then behind the UPVC upright and UPVC bar for the roof up-to the centre of the roof - then inside the centre beam for the roof - and into the fan/light. I guessed that - I needed to trace the other heavier gauge cable entering at the back of the double socket - as, I assumed, this must be where the circuit is fed. This didn't go well.

When I use the tone-generator connected to Earth and either Neutral or Live... I get convincing evidence that the cable is in the cavity of the low conservatory wall... but I also get a fainter tone over the majority of the house - including places no-where near the cable - e.g. in the middle of the upstairs bedroom 2m from any wall and 1m from floor and ceiling. If I connect the tone generator to the live and neutral wires, it is only detectable over a more constrained region of the house... but it doesn't seem to to trace to anywhere near other sockets... and I can't find any junction boxes. Using the tone generator, in this configuration, I can establish evidence that all the sockets in the conservatory are connected to one-another... but I can't find where any of the conservatory wiring might be connected to mains electricity in the house. This makes no sense to me - as mains in the conservatory had worked perfectly until very recently. Before anyone asks... no DIY has been done between it working and not working.

While my tone-generator experiments were reasonably convincing in showing me that my conservatory sockets were connected in common... it also showed me that they weren't in common with other sockets - or with lighting circuits - in the house. This makes some sort of sense... because conservatory electrics don't work now... while house electrics do work. This leaves me completely bemused. I've looked inside the sockets in the house that are closest to the conservatory - but haven't found any loose/disconnected wires. If there is cabling from the conservatory entering the house, I'm unable to find where it runs. I'm extremely confused... and hesitant to think my conservatory has drawn a 240v supply from the supernatural realm... despite that seeming to be the only explanation that matches the evidence I've found.

I'd welcome any hints... but perhaps these questions are relevant:

• What would be standard practise when adding electrical sockets to a conservatory where there's an existing (previously wired) house to which it adjoins?
• Am I right in thinking that, if all the switches in my RCU are in the 'on' position - then the RCU is showing no fault? (I've only experienced RCU modules that trip on earth leakage... but, I assume, it's conceivable that the modules themselves could fail? Is there an easy way to test?
• Would a professional electrician have better tools than my tone-generator/wand (which was cheap) for tracing wiring in a situation like this?

Am I missing something extremely obvious? Am I in a situation where I need a pro? (How expensive should I expect this to be if so?)

 

[littlespark]

Yea, an electrician will have better equipment to hunt down where the problem is, and more importantly, the experience to know what the readings are telling them.

As with any work, the original connection to existing wiring would have been done in the easiest and least disruptive route.
Which could be the downstairs sockets in the adjacent room, or indeed the upstairs… if it was easier.

The connection may be in the back of an existing socket, or from a joint box under the floor.

Check in the nearby rooms or the conservatory itself that there isn’t a switch fuse that’s simply been turned off, or fuse blown.
It may be that the conservatory is a fused spur off the house ring.

 

[ASteve]

Yea, an electrician will have better equipment to hunt down where the problem is, and more importantly, the experience to know what the readings are telling them.

As with any work, the original connection to existing wiring would have been done in the easiest and least disruptive route. Which could be the downstairs sockets in the adjacent room, or indeed the upstairs… if it was easier.

The connection may be in the back of an existing socket, or from a joint box under the floor.

Check in the nearby rooms or the conservatory itself that there isn’t a switch fuse that’s simply been turned off, or fuse blown. It may be that the conservatory is a fused spur off the house ring.

Thanks for the reply - though it mostly just confirms that I've got the problem I've got. Downstairs I don't think wiring could be sub-floor - as the floors are solid concrete. Upstairs there are floorboards - but having lifted them I can't find any wiring or junction boxes. I've looked inside all the nearest sockets... but nothing plausible-looking emerged. It was at this point I decided I was baffled.

From just your words, "It may be that the conservatory is a fused spur off the house ring." this scenario sounds likely to me... especially as there is a fused switch in the conservatory. I thought it was just for the light/fan - but, as that's remote controlled in normal use, the switch has been on all the time... so I might not have noticed if the switch also turned the sockets off.

I've checked the fuse in the switch in two ways: I checked it using a multimeter (it has low resistance) and I checked it by swapping it with the 13A fuse in a power drill. It checked out as OK both ways. While it seems a long-shot, perhaps the switch has failed... I guess I could verify this by (carefully) using a multi-meter - to find out if mains voltage is present at the switch. If the switch has failed, and if it is a switched spur... I guess I'd have found the fault. I remain bemused about where the cables might be routed in the conservatory. I can't see where they enter the house - upstairs or downstairs - in any of the 4 adjoining rooms. I also can't work out (if there's only one mains cable from the house to the conservatory) how the gap is bridged across the gap in the conservatory wall for the external doors.

If I give up - declaring this too difficult a puzzle for me... any idea how much I should be paying a professional electrician to tell me what's wrong?

 

[DefyG]

The fused switch at 4 o'clock has one larger and one smaller twin-and-earth cable.

This would indicate to me that if all the sockets have 2 cables (thicker ones), the conservatory is a radial circuit and the 'fused switch' is just to isolate the fan light (probably should be a 5A fuse though)

So as a radial circuit presumably fed from the ring circuit I would be looking for another 'fused switch' whereby the conservatory is de-rated from the 32A ring final circuit.

If you are sure there is nothing inside, is the an adjacent external point, socket or S/FCU where the conservatory could have been supplied from?