Hiding meter tails in walls, sufficient mechanical protection

[1Justin]

522.6.101(iii) requires trunking 50x50 to BS EN 50085-2-1 .

But mechanical protection (iv) : We agree that mechanical protection is "difficult to provide" and we are advised here of 3 or even 5mm steel.

The lid of the BS EN 50085-2-1 trunking is not this thick, yet that trunking could be hidden in wall and used for mechanical protection. - So saying this, then could I use ONLY the galv lid of such, screwed in place to cover meter tails which were channeled into blockwork behind dot and dab?

(single brick wall, loadbearing, slightly dodgy, definitely not thick enough to risk channelling for 50x50 trunking)

.. I could of course go to the steelyard and get a length of 5mm plate, only it seems these nice galv lids are just available.

Justin

 

[HandySparks]

It may be applying the rules in an unusual way but I would say yes, you could use just the cover providing that it's earthed. I'm not sure exactly what "satisfying the requirements of these Regulations for a protective conductor" would entail in this situation. Depending on how you do it, the earthing connection to the trunking cover would probably have to be accessible.

I assume that you're saying "522.6.101(iii) requires trunking 50x50 to BS EN 50085-2-1 ." because you can't obtain any smaller metal trunking?

 

[Richard Burns]

The key issue here is that the mechanical protection does not need to be earthed, all the other options (which are not mechanical protection) must be earthed.
Also the statements are ENCLOSED in earthed metal; a lid of trunking will not enclose, only cover and you already state the wall is too thin for 50x50 so would the cable be greater than 50mm deep from the other side?
Could possibly use two trunking lids folded so they met on either side, but then you might as well use earthed metal conduit.

 

[Knobhead]

I’ve got to ask why do you want to bury the tails?

If you have to get from the meter to a remote board you have to incorporate OC & EL protection. Why not proceed from there with split concentric or armoured installed in a normal fashion?

 

[1Justin]

The single brick wall is between hallway and what was internal garage. Internal garage now converted (building control) to living room.

Customer wants to move the electricity meter out into to the understairs area and we are getting a price from DNO for this. (We would leave CU in place high on the living room wall where it could be lost in a bookshelf).
Customer doesn't want trunking down the wall which will be dot-dabbed. Room is not very big, so we are minimizing thickness build-up on that wall. I only know of 50x50 minimum size trunking in BS EN 50085-2-1. If we could find (say) 20m deep tunking then I'd use that for the tails, only it doesn't seem to exist. It's a single brick wall supporting room above and we'd sooner not mess with it - other than perhaps a very shallow chase to loose the tails.

There would be >50mm of brickwork remaining the other side of the (shallow) chase, so technically just a mechanical protection from the dot/dab (living room side would suffice).

I think I would earth the cover anyway even though regs would say I could get away without. I'd bolt an eye to it and this could be accessible from the CU enclosure/cupboard. I'd technically also need a short (120mm) piece of conduit throgh the wall, and as this would need to be earthed.

Hi Tony: we think that 25mm SWA would definitely too big and stiff to loose in this wall. Concentric is just fine, but protection wise it requires the same as standard 25 tails plus separate 16 earth, and would be more bulky and less flexible.

 

[malcolmsanford]

Theres always MICC

 

[1Justin]

MICC. Really? - "No additional mechanical protection required to meet BS 5839-1 (02)". Isn't that purely mechanical protection under fire regs? - Surely not for mechaniocal protection (nails etc) ESQCR/17th ed'n.
- It's copper covered isn't it?

Anyway 25mm MICC whoa ££

Thanks

 

[Deleted member 26818]

Mechanical protection is only required if an earthed sheath or earthed containment is not being used.

 

[imago]

What about running each tail in galv conduit? It would provide protection, but still be within the thickness you need. Bonded together and then earthed all should be well.

 

[Knobhead]

What about running each tail in galv conduit? It would provide protection, but still be within the thickness you need. Bonded together and then earthed all should be well.

That would create eddy currents.

 

[johnboy6083]

What about running each tail in galv conduit? It would provide protection, but still be within the thickness you need. Bonded together and then earthed all should be well.

it wouldnt all be well mate. The eddy currents would probably melt the cable you used to bond them together. All phases and neutral must be in the same hole if passing through ferrous metal. If seperate holes must be used, then a slit must be cut between all holes, to cuit the lines of magnetic flux.

 

[johnboy6083]

just beat me tony

 

[imago]

Very true, I must make a note to think before typing.

 

[UKMeterman]

Unless you bond one of the lengths of conduit at ONE end only...

 

[malcolmsanford]

MICC. Really? - "No additional mechanical protection required to meet BS 5839-1 (02)". Isn't that purely mechanical protection under fire regs? - Surely not for mechaniocal protection (nails etc) ESQCR/17th ed'n.
- It's copper covered isn't it?

Anyway 25mm MICC whoa ££

Thanks

You think you would need 25mm MICC look at current carry capacity for MICC.