Tails in cavity wall

[catdog1121]

So I have a consumer unit to change, the consumer unit was in the garage but it has been converted to living accommodation years ago. The utility cupboard is on the outside wall, the consumer unit is obviously on the inside wall but near the ceiling.

The issue is when they changed the garage to living accommodation they created a second skin using breeze blocks. The tails from the utility cupboard were run in the cavity wall between the meter cupboard and the consumer unit, these tails need upgrading to 25mm plus 16mm earth.

I know just running new tails in the cavity will not provide enough protection, the cables would be less than 3m so from a DNO point of view thats fine. Its going to be hard enough to run the 25mm cables through and up the cavity wall let alone put any sort of copex to protect it, the alternative is 25mm 3 core SWA however then would need a fused isolator box in the meter box to terminate. (Can't find any sort of wiska box that would be able to make connection from tails to 25mm 3 core SWA).

Im sure I am not the first to come up against this issue so thought I would see what others thoughts were.

 

[Dustydazzler]

I don’t think it’s an issue to utilise the ‘existing’ tails set up so long as the are the correct size csa
However
If like you , they need to replace the tails I don’t think pulling up in the cavity will be acceptable practice nowadays due to lack of rcd protection

 

[Octopus]

What is your reason to upgrade the tails?

 

[Wilko]

Hi - If I understand Regs 522.6.202 and 203 correctly, if the cables are more than 50mm deep from both sides and there are no metal parts in the wall then the cables do not require RCD protection. Happy to hear if I’m mistaken .

 

[Midwest]

The only issue I feel with dragging any cable in a cavity, is damage being done to the cable unseen. Before anyone says anything, the bit coming out the end, may have missed the cavity tie etc, but the bit inside may have not.

That said, I I've pulled meter tails through a cavity over a short distance (less than metre) in flexible conduit. If it goes in freely, should be okay

 

[telectrix]

So I have a consumer unit to change, the consumer unit was in the garage but it has been converted to living accommodation years ago. The utility cupboard is on the outside wall, the consumer unit is obviously on the inside wall but near the ceiling.

The issue is when they changed the garage to living accommodation they created a second skin using breeze blocks. The tails from the utility cupboard were run in the cavity wall between the meter cupboard and the consumer unit, these tails need upgrading to 25mm plus 16mm earth.

I know just running new tails in the cavity will not provide enough protection, the cables would be less than 3m so from a DNO point of view thats fine. Its going to be hard enough to run the 25mm cables through and up the cavity wall let alone put any sort of copex to protect it, the alternative is 25mm 3 core SWA however then would need a fused isolator box in the meter box to terminate. (Can't find any sort of wiska box that would be able to make connection from tails to 25mm 3 core SWA).

Im sure I am not the first to come up against this issue so thought I would see what others thoughts were.

if tails are 16mm, i'd leave them alone (apart from connecting up to your new CU.). tin hat on.

 

[Dustydazzler]

if tails are 16mm, i'd leave them alone (apart from connecting up to your new CU.). tin hat on.

If it’s just a simple like for like board swap I tend to agree

(Jumps back into bunker)

 

[Wilko]

And if it’s a 60A main fuse the 16mm tails are fine no matter what load the Customer puts on it.

 

[Jon Bateson]

Yep leave em be. What’s the earth arrangement? And csa ?

 

[Charlie_]

Any idea what size the main fuse is?
Maximum demand?

 

[catdog1121]

Its TN-C-S with 100amp cutout fuse (Although might only be a 60 or 80 amp fuse in the carrier but says 100amp so have to presume). Tails look really small, have not taken it apart but looked at next doors that had been cut off and I would say they are 10mm tails so really need upgrading. I thought the regs say they only need RCD protection if more than 3 meters, cable length will not be more than 3 meters, but thought there had to be some mechanical protections.

How about a large wiska box with a couple of henley blocks inside to make connection between tails and swa?

Saying that trying to get even 2 core 25mm SWA though the cavity could be a problem so may not have a lot of choice.

 

[catdog1121]

My guess is that the consumer unit was just the other side of the wall so was not an issue but when they did the conversion the cut all the twin and earth shorter and moved the cables up and put the consumer unit at the top so it did not get damaged... It was either done by a cowboy builder or a very long time ago as its an old wylex rewireable consumer unit.

 

[Jon Bateson]

I would just pull flexible tails in. If it’s back to back with board what’s gonna happen ?

 

[Ian1981]

Its TN-C-S with 100amp cutout fuse (Although might only be a 60 or 80 amp fuse in the carrier but says 100amp so have to presume). Tails look really small, have not taken it apart but looked at next doors that had been cut off and I would say they are 10mm tails so really need upgrading. I thought the regs say they only need RCD protection if more than 3 meters, cable length will not be more than 3 meters, but thought there had to be some mechanical protections.

How about a large wiska box with a couple of henley blocks inside to make connection between tails and swa?

Saying that trying to get even 2 core 25mm SWA though the cavity could be a problem so may not have a lot of choice.

If you think that tails need rcd protection for being over 3 meters you better read again.
Why would you even think that?

 

[catdog1121]

Sorry yes over current protection is required was from reading an above post not RCD, this is a requirement from DNO if tails are longer than 3m.

My alternative is run the cables straight through the wall then use trunking up to consumer unit but dont think that would go down too well with customer.

You can get some 50mm double walled pvc copex which would protect the cables from installation damage at least

 

[Midwest]

Whenever I did a consumer unit replacement, the old tails were never long enough, so 25mm etc were always installed.

 

[Octopus]

OP - what is your estimate of maximum load? How is the property heated?

FWIW I would leave them well alone.

 

[Deleted member 26818]

You may have to re-drill the holes at an angle, to allow the cable to pull through easier.

 

[catdog1121]

Its a 3 bed semi so maximum load not going to be massive but they do want to add power to an outbuilding. 10mm tails really should be replaced imo. I know the OSG says 25mm but 16mm for most would be ok but 10mm is probably pushing it a bit too much.

I think it will be a case of do what I can but think just getting 25mm tails through the cavity will be enough of a challenge let alone thinking about anything else.. The regs are all very well but in the real world...

 

[hasel5]

You may be surprised how easy the new tails pull in especially if you prep the hole each end and do a tapered joint