Tails in cavity wall

[Wilko]

I’ve used it but you can drill through it with an sds quite easily so I’m in two minds whether it compliant for mechanical protection

Hi - agree it’s possible to drill through. I’m thinking that 522.6.204 (iv) doesn’t require the protection be drill proof, just prevent penetration by nails and screws. I’m relying on the British manufacturer who recommends it for this job. Maybe I’m too trusting?

In the end it would be better if the tails were not there in the first place.

 

[catdog1121]

So you looked at the tails next door to establish what is required in the house you are working on?

Next doors had the same size tails that had been replaced but cut at the wall so could see the size of the conductor.

 

[SparkieMarky]

I would agree that running tails in a cavity or any other cable is bad practice for a number of reasons including:

1) Possible unseen damage to cables pulled through the cavity over the hidden portion.

2) De-rating factors should insulation be present or added to the cavity at a later date.

3) The cavity (if it hasn't already been filled with crap already from the bricky) is a potential chimney. So should there be an issue with the installation and an electrical fire starts in the cavity then the fire integrity of the building could be compromised.

4) Even before things like Part P and the good old competent person schemes existed I believe that the old NICEIC Technical Handbook used to specifically frown on the practise of any cables being installed in cavities and it would have been considered poor workmanship if the practise was used.

So for what it's worth if the metre cabinet isn’t on the front elevation of the house and there is not neat and tidy way of routing the tails indoors, (taking account of requirements for suitable earthed mechanical protection etc. if buried) then I would go down the route of external SWA clipped direct on the exterior wall and through wall directly into the CU.

 

[catdog1121]

The problem is even externally its in a narrow passage shared between two houses leading to gardens which again is not ideal. Added on to that DNO's don't like any customer equipment in their boxes. Its one of those between a rock and a hard place because of the alterations made. I think the best solution is to try and feed some kind of copex even if just pvc 32mm, at least it gives it some protection from future insulation or falling debris.

Remembering there is a utility box on the outside and consumer unit on the inside there is no real risk of anyone wanting to drill through the wall in that position.

Given its only a 3 bed semi and using 25mm tails de-rating will not be an issue.

 

[Old Tiler 43192]

If the cut out is 100A then 25mm tails are mandatory irrespective of load (taking into account diversity).
No cables are allowed in a cavity other than meter tails 'which must pass directly through i.e. perpendicular to the wall'
So the choices are you either run up the outside then go straight through the wall, or through the wall then up the inside (both with suitable protection for the 'up' bit)
And if the total length will end up more than 3m, then you need to provide overload protection to that run.
Those are the rules, the customer has to be told to like it or lump it.

 

[loz2754]

Hi - agree it’s possible to drill through. I’m thinking that 522.6.204 (iv) doesn’t require the protection be drill proof, just prevent penetration by nails and screws. I’m relying on the British manufacturer who recommends it for this job. Maybe I’m too trusting?

In the end it would be better if the tails were not there in the first place.

View attachment 49504

Electrical safety first recommends minimum 3mm steel for this application

 

[Bobster]

If the cut out is 100A then 25mm tails are mandatory irrespective of load (taking into account diversity).

Care to share the regulation that states this?

 

[DPG]

No cables are allowed in a cavity other than meter tails 'which must pass directly through i.e. perpendicular to the wall'
So the choices are you either run up the outside then go straight through the wall,

Not sure what you mean here - any cable can pass directly through a wall.

 

[Old Tiler 43192]

Care to share the regulation that states this?

OSG 2.2.3.1 Consumer's Tails, 2nd paragraph. '...and the minimum cable size should be 25mm"

 

[Old Tiler 43192]

Not sure what you mean here - any cable can pass directly through a wall.

Yes, but not run in a cavity. You're right, any cable can pass perpendicularly through the cavity, it's preferred that meter tails do so also, however they are the only cables that may deviate e.g. enter the cavity then go up slightly, then exit, recognising that we don't live in an ideal world.

 

[Ian1981]

OSG 2.2.3.1 Consumer's Tails, 2nd paragraph. '...and the minimum cable size should be 25mm"

That is not a regulation, mearly guidance going to a default csa for fuses that are rated at 100 amps.
There’s no such regulation preventing you using say 16 mm tails as the fuse could be rated lower than 100 amps

 

[Bobster]

OSG 2.2.3.1 Consumer's Tails, 2nd paragraph. '...and the minimum cable size should be 25mm"

The OSG is a guide, nothing more. It is not regulation.