Thatched wiring - ways to make safer

[Mick-J]

Well....wiring in a 1750s thatched cottage attic, not wiring made from thatch
One we have been letting for over 20 years (as well as enjoying ourselves!)
I have read Thatch Roof Wiring - https://www.electriciansforums.net/threads/thatch-roof-wiring.106532, but welcome any ideas for us.

We occasionally have mice in our attic space (as any thatch will). Ideally we would like a thatch roofspace with no wires. But we have some. Regular cables to lights.
Our electrical certificate needed refreshing this summer, and the electrician we got was pretty thorough (although admitted to being unfamiliar with any special requirements regarding thatched properties).

He did, however, flag up some concerns over the "insulation resistance" of the upstairs lighting circuit.
The value seen on the circuit was 2.5MΩ. Apparently below 1 is a direct 'fail'
As comparison, the downstairs lights were 55....the cooker 500, the hob (directly behind the consumer unit) '>999'
He wasn't happy enough to give a 5-year certificate, so we only have 12 months, with the goal of 'remedying' things soon

The previous certificate was done after they had done some chunky work moving the main consumer unit from a hard to access space under the hob to go outside in the meter box....& all circuits are listed on that document as >200, which makes me suspect they didn't 'properly' test things That, or something has degraded massively & is at the point of failure

The house has two bedrooms upstairs, plus a 'new extension' bathroom off one: all with ceiling (& wall) lighting. Also a cupboard with lighting and a wall light over the stairs.

I am not a sparks, but we are considering solutions to this - ultimately, we want the place to be as safe as possible....albeit ideally without thousands of pounds of work We already removed the woodburner for a quality electrical replacement for safety reasons.

He has a couple of ideas which we will examine more later this week.

First one: to run SWA cable up into the attic, to replace all existing 'regular' plastic power cables.
SWA into some kind of ceiling 'light boxes' in the rooms below, where their can be junctions (none allowed now in the attic).
Using some 'kinetic' switches in the rooms to be able to power the lights without any physical connection. I've not found any that connect to 240v lighting, only some that connect to 12v under cupboard-style lighting. If anyone has pointers for those, I'd love to hear!
Sounds like we would need a fairly chunky box for the cabling to be done in the rooms below, & their ceilings are not that high....

Second one: to examine options for conduit. This might sound the simplest, but I believe might still require perhaps significant rewiring in order to get cabling into it - unless anyone can suggest conduit that can be wrapped around existing cabling? (which I feel would be a brilliant solution!)
He appears less keen on this....ultimately, our attic is relatively small, & perhaps the first option 'sounds' the easier & safer?


Has anyone here undertaken either of these....or indeed undertaken work to remove perhaps all wiring from the attic space below the thatch?
We cannot put wiring under the flooboards, because the rooms below are under the floorboards.....the joys of an old cottage.

Someone else mentioned Pyro/MICC....but they sound very specialised (from what I am reading!).

I'm also toying with how we could remove all attic wires - perhaps running wall lights from sockets, but the bathroom and staircase lighting might be harder (no sockets)
Another might be to monitor that resistance value to see if it has actually always been around 2.5 - I have no real idea how bad that is, or if it might be fine for the next 50 years....I suspect that the RCDs should trip IF a mouse were to nibble through, & given the cables are on the floor of the roofspace, away from thatch, that the risk of incident is fairly low.

Any hints, tips, dos/don'ts, etc, gratefully received.
& obviously we will be guided (driven?!) by the electrician: just fishing for ideas and experience other have.

 

[littlespark]

Very good thought processes here, concerning fire safety and rodent damage.

Removing electrical joints from within the attic space reduces the chances that a loose connection causing arcing could ignite the thatch.

SWA would certainly stop the little blighters getting to the wires, but once the outer sheath is nibbled away, the steel strands of the armour then become susceptible to moisture and can rust through.
Maybe not so quickly in an attic as it would, say, underground.

Pyro is a brand name of MICC (mineral insulated copper cable…. Or something like that) and is indeed almost bulletproof. Fire retardant, tooth proof and, as you say, specialist and very expensive.

Try searching for “quinetic” instead of kenetic. Again, it’s a brand name, but some on her swear by them as a solution to difficult cable routes.
Stair lighting is possible, as you can just pair two switches to the one controller.



Ever thought of replacing the thatch with corrugated iron sheets?

 

[pc1966]

Another couple of thoughts for attic wiring is to consider using Flexishild cable, it has a fairly tough outer sheath but otherwise is not too difficult to work with and one of the guys I know who does a lot of farm work recommends it to help deal with rodents.

Another thing you might want to consider for a high fire risk area is to have the circuit protected by an AFDD (arc fault detection device) which are now being mandated for certain classes of building, though more for socket circuits. They cost around £50-100 more than an RCBO but price is gradually falling.

MICC/pyro is indeed a solution that would last - probably a couple of centuries if unmolested! However, it is expensive and few folks now use it as for its most common use-case (fire alarm circuits where fire survival is needed) then the FP200 style of cable is cheaper and far easier to install.

Another traditional and totally rodent-proof solution is metal conduit. That then has PVC wires, etc, pulled through. These days it is normally seen only in industrial situations where mechanical strength / impact resistance is important, or occasionally if someone is wanting them seen for a steam-punk sort of look. It needs some skill to install, and I doubt that some "domestic installer" electricians would do that, but your more traditional spark would certainly have learned how to do so even if they rarely do it now. The "conlok" style of fittings are similar to those commonly used in the USA for light duty work and make installation much simpler and faster (no threading of ends, etc) and would be fine for a situation such as attic cabling.

Just to add - SWA is tough like conduit, etc, but terminating the ends usually needs a bit of work (glanding to suitable boxes, etc) and is not that suited to accessories like lights. However conduit has end-boxes available that are intended for things like pendant lights and so on to be attached so might work out easier to use overall.

 

[pc1966]

Just to add that FP200 is similar to Flexishield, though they have different intended use-cases. Both have a foil outer and bare earth drain-wire and that would help ensure that if damaged or nibbled then the RCBO should trip on the earth-fault even if current low.

The 2.5M resistance is suspiciously low: either damaged or poor cable, or damp & dust in some junction box or accessory.

 

[pc1966]

Here is a link to a PDF with some guidance, as the older forum thread's link is now broken:

https://nsmtltd.co.uk/wp-content/uploads/2019/01/2.-Electrical-Installations-in-Thatch-Pamphlet.pdf

 

[davesparks]

First thing I'd do is find the cause of the 2.5megohm reading if you are concerned about it.

Planning a rewire to cure something that could be caused by one aged light fitting seems a little extreme.

Whilst 2.5megohms sounds low don't forget that is still 2.5 million ohms which, if it is purely resistive, will give 0.0001 amps of leakage current at the upper supply limit of 253Volts

Personally I would only trust steel conduit or MICC to be rodent proof.

 

[snowhead]

Also before you go deciding on a plan and spending thousands on it, check with your building insurer to see if they have a prefered installation method, or guidance or want photgraphic evidence.
You may even get a reduced policy cost.

 

[Mick-J]

First thing I'd do is find the cause of the 2.5megohm reading if you are concerned about it.

Planning a rewire to cure something that could be caused by one aged light fitting seems a little extreme.

Whilst 2.5megohms sounds low don't forget that is still 2.5 million ohms which, if it is purely resistive, will give 0.0001 amps of leakage current at the upper supply limit of 253Volts

Personally I would only trust steel conduit or MICC to be rodent proof.

Thanks for all the replies, much appreciated

Good point about asking the insurer. That said, they were the reason we removed the log burner. One year they told us to put a steel liner in the chimney - okay, a grand spent….then the very next year they told us it needed insulating from the chimney. We gave up on that
We also read that over 97% of thatch fires started from the wood burner….so removing that should minimise one risk.

@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!
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?
Please note - I am not suggesting I take on the role of an electrician - he used a chunky looking box to test things - just aware I can check things whereas he would ideally want to come in, do whatever is needed, then move on!

It is an old cottage, although the extension which includes the upstairs bathroom was put on around 25years ago.

Interesting to hear about the AFDD. I will check whether that can be added to our CU, which is only 10 years old.

If so: would a good lower cost approach at this stage perhaps be to
1. Deploy an AFDD
2. Pop a wireless smoke alarm (we have a bunch interlinked ones) in the roof space for warning purposes)
3. Monitor the resistance reading to see how that goes over the next 12months
4. Have a crawl around the attic: check (& document) how the cables run in prep for any future changes. Ensure they are over 300mm from any thatch, perhaps.
5. Check light fittings

I imagine that might just be deferring the major work, but given we have no reference point to know if it has always been low, I wonder if that would make sense?

 

[Dustydazzler]

Roll out the Flexi-Con

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

www.tlc-direct.co.uk

 

[Mick-J]

Roll out the Flexi-Con

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

www.tlc-direct.co.uk

Interesting….although would require rewiring (can’t slip it over existing cable).
I was rather hoping there might be a steel conduit that existing cables could be tucked into

Any thoughts on my idea of following steps 1-5?
Cheers

 

[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)

www.tlc-direct.co.uk

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?