enclosing cables in conduit

[shobo]

Dear all
Does anyone have experience please of installing conduit onto pvc cables in a roof space, to prevent mice / rat attack ?
So, that's regulations, experience, materials, cost, etc.
It does sound DIY-able but I can imagine that might not be recommended.
Many thanks

 

[fernicarry]

Suspect if its stopping vermin you want then you'll need steel conduit, PVC would be sacrificial at best. But steel is a whole world of pain, needs to cut, bent and threaded, careful earthing required etc.

Pulling cables into conduit is hard, you need to minimise bends and make it way bigger than you imagine to stand any chance of drawing cable through. I put some T&E in plastic conduit in my shed more for aesthetics than protection and it was a right faff assembling it, it'll never be accessible without pulling it all apart. I've also put a lot of CAT cables and the odd bit of fibre into PVC conduit so that I can re-feed in the future in areas I don't have easy access to. Even with those relatively thin cables you still don't get much into the conduit before it all jams up. If you check the OSG (IET On-Site Guide) there are tables on stuffing percents.

If you use steel you are allowed to use singles -- as opposed to twin and earth -- because the conduit provides the mechanical protection and may also provide the earth (calcs need to be made) so that makes for less bulk to stuff into the conduit. The conduit would need to go all the way from the fuse box to whatever its driving though, or changeover at an adaptable box before you enter the high risk area. Going through a junction box means more connections to possibly fail and earth continuity to worry about. Regs say that junction boxes must be accessible for periodic inspection (I refuse to believe in maintenance-free boxes).

Under Part P (I'm in Scotland so our regs are a bit more relaxed in some cases) you can probably DIY it under the replace-existing-like-for-like justification. But IMO you'd want to use a registered sparky to be sure of getting it right if using steel.

I read once that cables now have a very bitter substance added to the sheath to discourage munching. Can't find a reference now. We've had old cables stripped right down to the copper but none of the new cables that I've put in in the last 5 years have been touched (to my knowledge...). We know we have nocturnal 'visitors'. They very much enjoy the foam insulation on the pipes!

If the cable is accessible enough to do this work then why worry about physically protecting it? Just make sure you have the right circuit protection devices to protect life and property and replace as and when it becomes damaged. And/or get a cat...

 

[shobo]

Thankyou Fernicarry for your very knowledgeable reply. (I have no electrical knowledge btw)
The reason for my enquiry, is that I may be acquiring a thatch property, where I know pvc cables exist in the loft.
The reason for my putting them in conduit is to satisfy insurance, but by no means just to satisfy insurance, but for my own peace of mind. I would do it even if insurers didn't require it.
Your reply indicating that the conduit has to go all the way to the consumer unit ? Golly, that sounds like a lot of work - like a major rewire ? Is there not a type of conduit that is mice-resistant and can be installed more simply ?
Atm, the pvc cables have a kind of cable tray placed OVER them. So, imagine a shallow cable tray, but placed over the cables instead of the cables laying in the tray. A bit odd !? Is that supposed to prevent straw falling onto a shorting cable ? Seems daft (The previous owner is no longer with us, so I can't ask her). In any case, although the loft is quite tidy, there is straw already fallen into the gaps between the joists and may be in contact with cables. I have no intention of persisting with this 'solution'.
For my peace of mind, until I can get improvements made, would the RCD activate if mice damaged a cable enough to present a fire hazard ?
What is your gut feel about the relative costs of:
-installing conduit,
-removing the cables from the loft, putting in wall lights instead,
-boarding the loft floor to cover the cables (obs not such a good solution).
Many thanks

 

[Flyfisher]

If it's just rodent protection that's needed, how about something like this: https://www.motoelectrical.co.uk/types/anti-rodent-insulation-tape/anti-rodent-rat-mouse-mice-proof-electrical-insulation-tape-honda-4019-2317-20m-1200450/

I've heard of such stuff but have never used it myself so have no idea how effective it is, but I'm pretty certain it would be far easier to install than metal conduit, for all the reasons fernicarry has mentioned. Metal conduit can be a DIY job, but you'll need the necessary tools for threading and bending the pipe - a plumbing pipe bender designed for copper pipes won't work (I know, I've tried!). On the few occasions I've needed some of our conduit altered I've called our electrician because he's all tooled up for such jobs and it doesn't seem to take him significantly extra time.

But if the insurer is insisting on conduit then that's a different matter (unless you try a different insurer?) and it might be worth getting a professional quote (or two) first, just to get a baseline cost indication. Another advantage of this approach is that the electrician would also 'sign off' the work . . . something that the insurance company might insist upon anyway, even if you DIY - in which case you'll need a certified electrician for that anyway.

 

[shobo]

thankyou flyfisher.

 

[fernicarry]

The cover over your cables as you say could be to stop dry straw falling onto hot cables, there are probably more qualified people on this forum who can comment on how things are typically done under a thatch roof and what insurers insist upon. If that's the major concern then you'd only need conduit in that vicinity but obviously the mooses could still have a chew elsewhere.

Cables do get hot under normal use. Regular PVC cable is good for up to 70', some types up to 90'. I wouldn't have thought this was enough to ignite straw. The problem would be under fault conditions, damage or overload, where temperatures could be significantly higher. If its just a lighting circuit then it shouldn't be possible to load it up very much at all without the breaker tripping so the risk should be low. An electric shower on the other hand draws an insanely large current for a moderately long amount of time so that would be one to pay a lot of attention to and reroute if at all possible. Similar but lesser risk for immersion heaters.

RCD's are mainly there to protect life in case of accidental contact with live conductors. They detect that some of the current has gone missing (cos its running through your body to earth rather than back to the RCD!) and disconnect very quickly, in well under a second. A rodent biting into a cable may cause one to trip, but then said rodent might well live to chew another day so its not quite the disincentive that being burned to a crisp is. Regular nuisance tripping would be something to investigate.

Getting the system checked over by a sparky would give you the peace of mind that the installation has been designed correctly and is in a safe condition. They can do an insulation resistance check that can indicate damaged cables. The kit to do this is relatively expensive but I'm keen enough that I bought my own. I had it out to fault-find the Xmas tree lights but that was a little bit overkill.

Caveat, I'm not a sparky, just an enthusiastic amateur.

flyfisher -- Capsaicin, thats the stuff I read about being added to cable sheaths and other PVC products. No idea if its standard practice or what. Anecdotally its older cables I've had trouble with even when they lie next to new ones.

Last winter we were catching mice in the traps under the kitchen units every few days. This winter we have a cat who literally makes the problem vanish, except for the odd squishy bit left behind...

 

[Flyfisher]

Flyfisher -- Capsaicin, thats the stuff I read about being added to cable sheaths and other PVC products. No idea if its standard practice or what. Anecdotally its older cables I've had trouble with even when they lie next to new ones.

Interesting. I don't know if it's standard practice either but I'm surprised the manufacturers don't make a bigger deal about it if it is. Perhaps it's a 'special option'? It certainly sounds like there is something different about your old and new cables though. Capsaicin is the 'hot' ingredient of chilli peppers and the like though apparently it only affects mammals so it's a good job we don't have cable munching birds to deal with!

 

[philpjuk100]

Did a lot of conduit as an apprentice, always used to bend it with a bit of timber with a hole in it.Conduit that's what apprentices are for!

 

[philpjuk100]

,

 

[Flyfisher]

That sounds like a good trick . . . how did you prevent the conduit kinking?

 

[philpjuk100]

Most sparkies had an old bit of timber, about 4x2 around four foot long with a "belled" hole at one end.They would just poke a length of 7/8" conduit through the hole and bend the conduit a little and move it slightly and bend again until they got the angle they wanted.The ends were then cut to length and threaded always lubricating the die with tallow.They always had a long length of piano wire with a loop at the end they called "the mouse" to pull the cables.I used to quite enjoy this but not "pyro" mineral cable.With conduit there was always the option of using an elbow with a removable cover to help with the pull through.Twin and earth through conduit will be very difficult,we used to use 7.029 and could pull nine cores through it with a bit of tallow to lube it and a lot of cussing!

 

[88v8]

Our insurers who increasingly want this n'that pertaining to our thatch, haven't raised the issue of cabling in attics. Nor did our electrician during the last inspection.
In one attic there are no cables; until I made a hatch no one had been up there for perhaps two hundred years, but the newer attic - 60s - contained many fine examples of professional electrical work from the 60s to the 90s. Cables randomly draped around with no clips, under and over loft insulation, junction blocks wound round with insulation tape.
I am completely sure that the immediate POs were not responsible for this, DIY wasn't their thing, and I'd say the same goes for the other POs I've met. No, this was the Trade doing what it often does when no one is looking.

I have clipped up what I can, deleted the junction blocks, unearthed it from beneath the insulation. Our mice, as has been said, fortunately prefer the pipe foam.
I asked our electrician to come and put it all in conduit. I understand now why he was less than enthusiastic!

Ivor

 

[Owain]

putting existing wiring in conduit that was never intended for conduit is going to be evil.

much easier to bite the bullet and poke some pyro through.