Should these tails be mechanically protected?

[Koreelec]

Hi guys.
Im moving a consumer unit for my brother and where I was going to run a 25mm armoured through the building he has decided to put a window directly above the cut out.

After explaining to him the only way I could do it would be to put a piece of earthed metal trunking on the inside (red line on photo) and bring a stud wall out 50mm, he's not happy with this as the wall would stick out too much to cover the trunking. After my advice, he has asked his friend what he would do and he said he wouldn't use the trunking and just clip direct to the wall??? Surely this isn't good practice with an incoming supply especially with it being tails?

What do you think?

 

[snowhead]

Do you mean clip the earthed sheath SWA direct to the wall?

P.S how are you going to cross over the gas pipe(s)?

 

[Dave OCD]

Assuming the meter box is outside where the tails exit through the garage wall couldn't you reroute them outside and in again enclosed in a suitable conduit - possibly waste pipe ?

 

[Koreelec]

Assuming the meter box is outside where the tails exit through the garage wall couldn't you reroute them outside and in again enclosed in a suitable conduit - possibly waste pipe ?

They don't want anything showing on the outside. Plus the gas meter is right next to the electric meter

 

[Koreelec]

Do you mean clip the earthed sheath SWA direct to the wall?

P.S how are you going to cross over the gas pipe(s)?

No clip the main tails direct to the wall. And the gas pipes are being moved

 

[Dave OCD]

They don't want anything showing on the outside. Plus the gas meter is right next to the electric meter

Fair enough.

 

[pc1966]

After my advice, he has asked his friend what he would do and he said he wouldn't use the trunking and just clip direct to the wall??? Surely this isn't good practice with an incoming supply especially with it being tails?

If they are the usual double-sheathed tails and are visible, then clipping to the wall is fine.

If there is any plans to cover them and less than 50mm from the surface they need either:

• 30mA RCD protection (a whole world of pain for random trips)
• An earthed cover able to blow the incoming fuse (<= 3m length) or any fused/switch you provide (> 3m) such as trunking or SWA
• Mechanical protection of at least 3mm steel to prevent screw/nail/drill penetration

 

[Koreelec]

If they are the usual double-sheathed tails and are visible, then clipping to the wall is fine.

If there is any plans to cover them and less than 50mm from the surface they need either:

• 30mA RCD protection (a whole world of pain for random trips)
• An earthed cover able to blow the incoming fuse (<= 3m length) or any fused/switch you provide (> 3m) such as trunking or SWA
• Mechanical protection of at least 3mm steel to prevent screw/nail/drill penetration

So if it's 50mm deep would you clip direct without mechanical protection?

 

[pc1966]

So if it's 50mm deep would you clip direct without mechanical protection?

Yes, you could as when deep enough then the regs don't require protection against shock from accidental penetration.

 

[pc1966]

Personally though, I would also look at the other risks of any damage as the consequences of shorting out the tails are serious!

If there are plans to make that area look nicer with new window, etc, then they might also be looking to clad the walls, paint them, etc, and so the issue of protection comes up once more.

The smallest of trunking is around 50mm, and that is a bit big for just tails, but equally 25mm SWA has a limited bend radius so you cant simple fold it tight after going through the wall. As a general guide the bend radius on most cables is about 8 * diameter.

A quick search has 25mm Prysmian 6181Y diameter as 11.3mm, but Doncaster lists 10-12.5mm as the range so you might get two through 25mm conduit, but the "boxes" for bends would be tight and really you would need to try something. If attempting it you really should get the 19-starand easy-fit Doncaster tails as far easier to wrangle. That would allow a cladding without too much issues afterwards.

Metal 32mm conduit exists but hard to find any accessories to match.

 

[pc1966]

Cable try with a metal cover, adequately bonded, is another option. Unitrunk do that sort of thing, so you could have 50mm wide and 28mm deep using the "medium" size tray (tray is 25mm, bracket 28mm).

https://unitrunk.co.uk/wp-content/uploads/2021/11/pg-56.pdf

I would also partly chase the hole through the wall so bend radius is better and inside the wall, not sharp as it comes in to any protection.

 

[Koreelec]

Yes, you could as when deep enough then the regs don't require protection against shock from accidental penetration.

I know it's not in the regs but 50mm isn't that deep and I just feel it's best practice

Personally though, I would also look at the other risks of any damage as the consequences of shorting out the tails are serious!

If there are plans to make that area look nicer with new window, etc, then they might also be looking to clad the walls, paint them, etc, and so the issue of protection comes up once more.

The smallest of trunking is around 50mm, and that is a bit big for just tails, but equally 25mm SWA has a limited bend radius so you cant simple fold it tight after going through the wall. As a general guide the bend radius on most cables is about 8 * diameter.

A quick search has 25mm Prysmian 6181Y diameter as 11.3mm, but Doncaster lists 10-12.5mm as the range so you might get two through 25mm conduit, but the "boxes" for bends would be tight and really you would need to try something. If attempting it you really should get the 19-starand easy-fit Doncaster tails as far easier to wrangle. That would allow a cladding without too much issues afterwards.

Metal 32mm conduit exists but hard to find any accessories to match.

Yeah I totally agree tbh I don't feel comfortable just clipping direct especially as they want cupboards on the same wall.

Thanks alot for your help

 

[pc1966]

If they plan to put something over the cable route then definitely should be protected as high risk of damage even during assembly of cupboards, etc, let along someone doing something to add shelf/bracket/light/whatever in the future.

I have no idea how thick those walls are, or how deep you could chase a grove for some SWA, but that might be the easiest and most conventional solution. Depending on the plans for the wall covering depth it might not need to be the full cable depth, and you might get away with clipping the cable in the grove with "half" of a cleat , or just some strips of aluminium and pair of rawlplugs, etc, crossing over it.

3C 25mm SWA is about 26mm, but if no more than 80A supply you could get away with 16mm CSA which is about 21mm dia. Even for 25mm cable you might go 2C and run a separate 16mm CPC to get slightly smaller diameter and thus bend radius.

 

[snowhead]

You can't chase 50mm into that wall, the block will only be 100mm at best.
Just go the depth of cables / SWA and plate over.

However you don't need to go 50mm if it's having wall board / plaster board dot and dabbed.

Alternately if the cupboards aren't going up to the ceiling run the tails surface across the wall just above the top of the cupboards, they won't be visible from the room.
You'll need to know the exact height of the cupboards or temp fix and level them up after the cupboards are up.

 

[UNG]

Hi guys.
Im moving a consumer unit for my brother and where I was going to run a 25mm armoured through the building he has decided to put a window directly above the cut out.

After explaining to him the only way I could do it would be to put a piece of earthed metal trunking on the inside (red line on photo) and bring a stud wall out 50mm, he's not happy with this as the wall would stick out too much to cover the trunking. After my advice, he has asked his friend what he would do and he said he wouldn't use the trunking and just clip direct to the wall??? Surely this isn't good practice with an incoming supply especially with it being tails?

What do you think?

Walk away and let his friend do the work as your brother obviously didn't trust your advice