Another running cable question.......

[JDLDIY]

Firstly I should say that I am familiar with the regs on running hidden cables in walls and that 99% of my cables have been run in accordance with the "150mm" rule or to accessories etc on the wall. I just have 1 cable which will need to comply with the other conditions i.e;

(a) enclosed in earthed conduit, trunking or ducting satisfying the requirements of
the Regulations for a protective conductor, or
(b) mechanically protected sufficient to prevent penetration of the cable by nails, screws and the like,

My question is, in plain English, how do I comply with either of these in the most straight forward way? Can I use galvanised steel capping and then does it need to be earthed? If so can I just run a bonding wire to a screw tapped into the capping above/below ceiling/floor?

Many thanks

JD

 

[ryanj]

Just use galvanised steel capping. Regulations don't require it to be earthed.

 

[ban-all-sheds]

No, but they do say "mechanically protected sufficient to prevent penetration of the cable by nails, screws and the like", and capping, earthed or not, does not provide sufficient mechanical protection.

Use round galvanised or BE conduit, or SWA.

 

[JerryD]

The regs DO require it to be earthed. 522-06-06

 

[plugwash]

note that you only have too satisfy one of those two not both (notice the or)

there is some argument over whether covered by earthed metal capping which encloses three sides of the cable can be counted as enclosed

and i doubt that capping would keep nails out so it can't be used to satisfy the second one

probablly the easiest option though you don't see it much is probablly actually one of the screened fire resistant cables like firetuff or fp200 but the stuff is significantly thinner than SWA and doesn't require glands to terminate though it is a bit more expensive than swa

 

[dingbat]

There is also another option, which is simply to make the cable visible. It's not the most aesthetically pleasing method but white PVC trunking or conduit can be installed quite neatly. Or if the run is out of the way anyway you could simply clip it direct to a surface. These visible options are often overlooked but sometimes they are the only practical way to do the job without increasing costs disproportionately.

 

[JDLDIY]

Well, thanks for your replies. What I really need is some capping which is strong enough to satisfy the requirement ie;

mechanically protected sufficient to prevent penetration of the cable by nails, screws and the like,

Basically the cable came within the 150mm requirement but then we removed a wall, so now it is not! What a pain. I am going to end up moving the cable as I don't want it visible but as it is my 10mm shower cable and the length of it should be kept down, that also gives me problems. B****r!!
I bet a lot of sparks would just put it in galvanised steel capping and have done with it, I mean why else is the stuff sold when it's easier to use the plastic version?

 

[plugwash]

10mm 3 core SWA seems the best bet if you want to keep the existing route

it will be a bit of a pain to bury the stuff but no worse than burying 20mm conduit

 

[biblio]

plugwash said:
'note that you only have to satisfy one of those two, not both (notice the or)'

1. So, what if the galvanised capping is properly earthed/bonded? Even though it may not be nail/etc-proof.

2. Could one get away with fitting say just an actual functioning light switch, in a wall to 'reveal' the possible presence of cable? Even though there might be say four other cables running vertically all up the wall but plastered in as well, and all within the width of the switch. Or would it need also a power socket lower down the wall too?

3. If cables were covered with say 3mm-thick steel strip, as long as this was at least 50mm wider both sides than the cable run, it would not have to enclose the cables would it, whatever the thickness of the wall?

 

[JDLDIY]

So, what if the galvanised capping is properly earthed/bonded? Even though it may not be nail/etc-proof

Exactly, so how would that be accomplished if acceptable?

Could one get away with fitting say just an actual functioning light switch, in a wall to 'reveal' the possible presence of cable? Even though there might be say four other cables running vertically all up the wall but plastered in as well, and all within the width of the switch. Or would it need also a power socket lower down the wall too?

Yes I believe that is more than acceptable and at the moment it is how I intend to proceed. The regs state:

either horizontally or vertically, to the point, accessory or switchgear on the surface of the wall or partition, to which the cable is connected

The regs go on to also say:

The installation of a cable in such a zone, but passing through the box of an accessory rather than connecting to the accessory, is generally considered acceptable.

So, there you go.

10mm 3 core SWA seems the best bet if you want to keep the existing route

yeah that makes sense but I just don't fancy the hassle of replacing the existing cable and then terminating it and having the headache of burying it also.

So, if I cannot find a way to adequately mechanically protect the cable, this is what I will do, sitting a light switch over the top with a double socket down below.

 

[plugwash]

note that it says THROUGH the box not under it

i think that this is deliberate to reduce the chance of the box being removed leaving the cable in place

 

[JDLDIY]

note that it says THROUGH the box not under it

Absolutely Plugwash, which also ensures that the cable is visible when the face plate is removed to look for cables.

 

[biblio]

I would like to know if it is acceptable or not to use galvanised capping in this 'blind' situation, if the capping is bonded to common earthing. Also is it also complying with the regulations to enclose cable within two sections of capping, with the first (back) piece fixed the 'wrong' way out (acting like a groove). Then fix the second (front) capping piece like a sandwich to clse the front. This would make the rebate in the wall twice as deep though.

 

[ban-all-sheds]

If you want to use capping, in any situation, no matter where the cables are, then you may. And you may use plastic, or metal, it's up to you. And the metal stuff does not need to be earthed.

The key point is that capping is a purely optional item, used to make it easy to hold the cables to a wall, and to protect them from the plasterer's trowel.

If you need mechanical protection to satisfy the wiring regs because the cable is in the "wrong" place, then capping is insufficient, and cannot be used, earthed or not.

 

[shaggy]

This has been discussed recently HERE
I think I was shot down for my views on how to earth the capping. It's still not completely clear to me why the regs say this:

(iii) be enclosed in earthed conduit, trunking or ducting satisfying
the requirements of these Regulations for a protective
conductor, or be mechanically protected sufficient to prevent
penetration of the cable by nails, screws and the like,

If earthed trunking or ducting is ok why is earthed capping not? If you drill through a piece of earthed metal before drilling through the live then does it matter whether it's ducting, trunking or capping?