Meter Tails - Protection

[Dave W]

Hi All,

Could do with some help. ASAP please

Am first fixing meter tails in new build, 25mm with 16mm cpc. Have come through wall from meter, chased in on internal side of wall and covered with metal plate. Where the tails run through ceiling void approx 150mm, do they need to be protected ? and if so how ? Once through the ceiling and the tails drop down the wall to the CU does this also need to be proteced ? and again how ?

A quick response would be appreciated.

Thanks,

 

[telectrix]

no need to protect tails in ceiling void or if surface to the CU, but a bit of pvc trunking would look neat above the CU.

 

[i=p/u]

maybe just put a barrier around the house when you finished.....

 

[wildgoose]

This is my understanding: If tails are buried in the plasterwork or covered up, then they must be mechanically protected if less than 50mm from the surface. As for any other situation, then you must do a risk assessment and make the call.
If it was coming through or next to a metal plate then why not install through a piece of robust plastic pipe for peace of mind.

Long tails greater than 3m will of course normally need an additional DNO fused isolator but discuss it with then and let them make this decision.

 

[i=p/u]

maybe just put a barrier around the house when you finished.....:6:

 

[Knobhead]

A quick response would be appreciated.

Thanks,

May take a bit of time to think about.

 

[Knobhead]

Just thinking about this, if the meter box is out side it won't be at ceiling level. What lengh are these tails?

 

[Dave W]

Just thinking about this, if the meter box is out side it won't be at ceiling level. What lengh are these tails?

Hi Tony,

Have pulled the tails through from meter box to CU position, they're currently 4M but will need to be cut down to suit so final length will be below 3.5M.

 

[telectrix]

if >3m, then a S/F should be fitted at source. if the DNO fuse in the head is 100A then you should fit a 80A S/F.

 

[rattlehead85]

Should be fine as is as long as you have earthed the metal plate you have used to protect them in the wall as required by BS7671.

 

[malcolmsanford]

The plate does not need to be earthed if it affords protection to reg 522.6.101. (iv)

 

[rattlehead85]

The plate does not need to be earthed if it affords protection to reg 522.6.101. (iv)

I would have thought if the plate was metal it would need to be earthed. Point iv however does not mention the protection being used as a protective conductor unlike points i , ii , & iii so your point appears to be valid. So would i be correct in saying that metal capping over buried cables does not need to be earthed as it is not being employed as a protective conductor and not deemed as penetrable by screws and nails. Somehow this doesn't sit right the fact that if a live tail and metal covering was penetrated without it being earthed the plate could well become live? which in itself would be a dangerous condition.

 

[malcolmsanford]

The metal plate is neither a protective conductor or in this case be classed as an exposed conductive part, it is purely there to offer mechanical protection to the buried cables.

Capping does not need to be earthed as again it is not a protective conductor nor is it an exposed conductive part. But capping is not deemed to be sufficiently robust enough to prevent penetration by nails, screws and the like, so the cable would need to have additional protection some other way ie RCD

There is no more danger to burying tails than there is to burying T + E really. Both are sheathed cable and therefore need the same protection. Granted a T+E does incorporate a CPC inside the sheath, but in order to trip a PD you would need to damaged both the LINE/CPC together, which is not always the case.

 

[Dave W]

To be honest I haven't earthed the protective plate, The tails behind the plate are also enclosed in flexible conduit so not too concerend with the plate becoming live at some point, also if it were earthed this would be plasterboarded over making the earth inaccessible so not that "dependable".

 

[Toonlad]

Recently on a new build for a firm im subbied too, had there NICEIC inspection. The job i was on had the tails coming through from the box on the side of the house and then up and accross the room. He requested the tails to be put into 20mm galv pipe with earth couplers at top and cross bonded down to nearest socket. The 16mm main bond ran in between the two pipes. He also said he would like the pipe to be cut at 45 degrees so then it would keep maximum protection for cable coming from pipe through wall into cutout /meter cabinet, so it didnt dig into the tube on exit.

Bit daft really 12 mtr tails, pulls for mechanical protection, and not wanting a S/F fitted lol.

Do what he said to the letter im covered.
Food for more thought.