cable routing question and wiring regs.

[Stephen H]

I'm aware of the rules regarding the appropriate routing of concealed T&E cables, i.e. within 50mm of wall edges/corners, in vertical or horizontal lines from a visible electrical accessory or greater than

50mm below a plastered surface. Anything else would require mechanical protection from drill bits, nails & screws and such like.

I was talking to a fully qualified sparky recently about my planned works.

He claimed that if the cable in question is protected electrically by a RCBO at the CU, none of the above apply and that if I really wanted to, I could run T&E in the gap between breeze/block wall and dot 'n' dabbed plasterboard from floor to ceiling with no mechanical protection at all, at less than 50mm depth from the surface and totally ignore the above cable routing rules.

Is the sparky factually correct or talking brown stuff regarding wiring

17th ed regs?

If he is correct, it offers me more cable routing opportunities given that I'm installing a CU fully populated with RCBOs only particularly for putting in a lighting circuit for the loft on its own RCBO. (this is deliberate in case I decide to have a loft conversion in the future so I was planning ahead regarding circuit design for this eventuality)

Slipping the 1.5mm T&E down between wall and plasterboard from loft to ground floor is actually an easier route than hacking access panels into a plasterboarded stud & partition wall, drilling holes in the noggins and reinstating the plasterboard panel cutouts and re-skimming the wall in order to have a cable route that obeyed the rules details in the first paragraph of this post.

Stephen.

[John Rumm]

either mechanical or earthed metal shielding; so a SWA may not have 3mm of steel round it, but the fact that the armour is earthed is adequate protection.

Its sounds slightly confused...

You can run cables at less than 50mm depth, and without additional mechanical protection. However they require RCD protection (with a trip threshold of If he is correct, it offers me more cable routing opportunities given

One option is to cheat - sticking an electrical accessory on the wall at an appropriate place to create the required zone is one option. That way you give a clue to someone drilling holes in the future.

However its usually fairly easy to go say up from a CU to a ceiling, thence across to a corner, and finally up through as many stories as required to the loft in the corner.

[harry]

I often think the "protection" issue is a load of bollocks. After all, the only protection that would actually protect would be steel conduit. All this plastic/thin metal tacky stuff won't protect against an electric drill.

I

[Tim Watts]

On Thursday 21 February 2013 23:28 Stephen H wrote in uk.d-i-y:

^^^^ 150mm aka 6"

That's internal corners only but also the internal top or wall/ceiling edge on the wall face too.

He's right about the 50mm bit, but he's talking complete bollocks about "ignoring the routing rules".

Any cable that does not have mechanical protection and is less that 50mm from the surface needs RCD protection.

If the cable has mechanical protection (metal trunking, metal conduit, is steel wired armoured (or foil screens to a particular standard and other condition are met) *then* you can route it where you like.

Or if it's on the surface and visible - then again, any way you want.

So with RCD protection at 30mA/40mS covering that circuit, directly or indirectly, you could run between the PB and wall but you still have to follow the horizontal/vertical from accessory or internal coner routing.

[Tim Watts]

On Friday 22 February 2013 08:01 harry wrote in uk.d-i-y:

The regs do define the level of protection.

But you have to remember that as long as the "thin tacky stuff" is properly earthed, it *will* provide protection as the fuse will blow/breaker trip with the touch voltage on the tool you banged through the cable not exceeding 50V for 40mS (IIRC).

[RobertL]

It depends on the type of bit. I think thin metal or certain plastics might protect against a masonry bit, which is what someone would be using to drill into the wall. Masonry bits are not sharp.

I once drilled into a wall and found I reached a point where I could drill no further. I tried drilling for a long time getting nowhere and finally discovered there was a cable there behind a thin metal strip.

Robert

[dennis]

Steel conduit won't protect you from a Bosch multi-material drill. They go through steel easier than the brick/block.

However conduit should be earthed and stop you getting shocked.

[tony sayer]

Den .. would you really be going into brick and or masonry with a drill capable of drilling steel and do you really have metal cutting masonry bits;?..

[John Rumm]

Plastic / thin metal capping is really only designed to protect cables from the over exuberance of the plasterer.

If you want failsafe electrical protection, then you need an earthed screen round the cable.

[dennis]

Why not? They drill masonry easily without needing to turn on hammer and hence make the drill last longer.

[Andy Wade]

Uh? How does "... or within 150 mm of an angle formed by two adjoining walls or partitions" [1] rule out external corners?

[1] BS 7671 reg. 522.6.6

[Tim Watts]

On Friday 22 February 2013 23:20 Andy Wade wrote in uk.d-i-y:

Probably because that's how the diagrams I've seen present it - I've not bothered to actually check the wording.

I shall do so tomorrow and double check the On Site Guide.

[Dave Liquorice]

You've not come across the Bosch multi drills then? They do drill virtually anything, light metal capping wouldn't be any challange at all, unlike a normal masonary drill. Conduit will make it think a bit but it's just an 'ard brick innit...

[tony sayer]

Tried those a while ago and wasn't that impressed...

[ARW]

The OSG gives no further info.

John Rumm updated

last year to show external corners after we had discussed the external wall angles/corners issue. We did take guidance from a registered body before John drew the picture.

The only thing missing from

is the flat screen TV on the wall:-)

[Tim Watts]

On Sunday 24 February 2013 04:44 ARW wrote in uk.d-i-y:

OK - That's interesting - thank you.

I may be remembering back to a diagram in one of John Whitfield's Pocket guides - which would have been an earlier edition.

Personally, I'm not hugely keen on either corner route as the average person has enough trouble not banging a picture hook in directly inline with an accessory - but there you go. Mind you I have made use of the ceiling band when a conduit had to deviate around an obstruction.

[ARW]

I did a job a couple of weeks ago. The guy had tried to fit a battery powered smoke alarm on the landing. Of all the places to fit the alarm he decided to fit it just under the CU (the CU was close up to the ceiling).

Christ knows why he he tried to fit it there as mounting it on the ceiling would not have needed the drill or the renewal of the cable he destroyed:-)

[ARW]

Blunt after 2 holes.