Thatched wiring - ways to make safer

[davesparks]

Must admit I am unwise as to the impact of such a low reading….& of course whether it has been that low for 20+ years!

Assuming it is PVC insulated cable and not some extremely old rubber or paper insulated cable then 2.5megohm reading suggests something like a little bit of contamination at some connections, a slightly leaky LED driver, and old lampholder in its way out, flourescent ballast.
Or it could just be that a lamp was left in a fitting by accident when the test was carried out.

Also not sure how we would check light fittings to find if they are causing the issue.
As an unqualified but reasonably competent person, are there any suggestions (or devices I can use) to check fittings, or indeed the resistance?

You would need an insulation resistance tester, this applies a voltage of 500V and measures the resistance in megohms.

Any electrician will have one and be able to find the cause for you.

The process they will follow is quite simple, you estimate where the middle of the circuit is and break it there, test each half of the circuit to find which half has the issue.
Then you split that half circuit in half again and re-test, and just follow this process until you find the cause.

 

[pc1966]

First thing I would suggest is making sure you have some flooring in the attic so you don't easily fall through the roof! Almost came a cropper myself a few years back when foot missed a beam

Without the equipment to test at 500V, etc, probably the best you can do is inspect the cables for any sign of damage (mice, or crushed, etc) and look for junction boxes, etc, that could be filled with dust, etc. Take care as you might find a cable that is exposed in a spot you don't see and then touching it will be BAD news. Even if you don't get killed by the shock due to RCD/RCBO protection, jumping in response and falling through a roof is potentially as bad.

While you can get metal trunking that could be fitted around exiting cable, it is not going to be practical to cover enough of it and you still have the problem of keeping mice out of that, so ends have to be pretty well sealed to gaps of few mm and realistically that means cables removed at ends, and by the point starting fresh makes more sense. You are probably not considering a total rewire, and it might be the only circuit in the attic is the lights, but if sockets are fed down from above then it is more to consider. Usually the biggest time/cost and trouble is routing wires through walls (where chased in / plastered over) so if mostly that is not needed then it might not be too expensive.

The 2.5M is not on its own a problem, it is more it indicates something is wrong and that could become a problem. It might be something like the cable is nicked against a nail/screw in to wood and that is your 2.5M path to Earth, but it might also be due to mice removing PVC insulation, etc. So it could be very cheap to fix if just dirt in a poorly covered junction box all the way to cables needing replacement.

 

[Mick-J]

Thanks again for both of your helpful replies
Food for thought and indeed discussion when we see our sparky fella on Friday

 

[Risteard]

Roll out the Flexi-Con

Flexicon 25mm Galvanised Flexible Steel Conduit - 10Mtr | Flexicon (FU25-10M)

You might need to remortgage the house to wire it in kopex.

 

[Mike Johnson]

As you say that the cables in the loft are "regular lighting" that would probably mean 1.0 or 1.5 T&E this existing cable could easily be pulled through 20mm Flexicon galvanised steel conduit, your electrician should know who its done and terminated into each light fitting.

 

[davesparks]

As you say that the cables in the loft are "regular lighting" that would probably mean 1.0 or 1.5 T&E this existing cable could easily be pulled through 20mm Flexicon galvanised steel conduit, your electrician should know who its done and terminated into each light fitting.

But to pull it through floppy conduit the whole lot would have to be disconnected and re-run so it might as well be rewired and made properly rodent proof.

Properly terminating the floppy conduit at light fittings and switches wont be all that straightforward either.

 

[Mike Johnson]

Only has to be disconnected one end and a draw cord pulled through then the existing T&E can easily be terminated in a standard stuffing gland, not rocket science although some on here think it is.

 

[nicebutdim]

Only has to be disconnected one end and a draw cord pulled through then the existing T&E can easily be terminated in a standard stuffing gland, not rocket science although some on here think it is.

I don't believe you've thought this through. Cables routed through walls/joists etc won't have been run to accommodate the significantly larger diameter required and will need to be pulled back to allow this work.

While steel flexible conduit is one means of protecting cables from rodents, in this instance I can't imagine fitting the stuff over existing cables being a worthwhile or economical endeavour.

 

[Mike Johnson]

I have thought this through, it is only lighting cables that are needing protection, these will be run from rose too rose so easily disconnected and pulled back and through a flexible conduit laid on and clipped too the surface of the joists, any cables that go through the ceiling can be terminated inside a box over the penetration.

So what is your better solution?

 

[Rockingit]

Personally, I'd have thought that the quickest/cheapest way to deal with this would be standard runs of galv tube, conduit outlet above where each light below is (can screw a 3 plate straight through the [wattle?] ceiling into it) and then use 2way 90's to jam down to trap the switch drops coming back up the wall. I'd have thought that they'd be fine, it'll be the loops that are nibbled through.

Or does nobody know how to use a bender anymore?