50mm Deep Chasing

[TheScullster]

Hi all

I have been considering how to satisfy 17th Edition wrt cooker cable. As I see it there are three options:

1 Fit RCBO in place of MCB for cooker feed 2 Use earthed steel conduit protection 3 Bury cable 50mm below wall surface.

That got me to thinking about the stability of the wall if option 3 is used. Allowing for plaster covering, but also the cable thickness means you will be chasing to a depth of half the inner leaf thickness. Also, with cable coming from above, the chase will extend 1/2 to 3/4 the height of one storey.

So, the question is, is option 3 above actually directed at modern domestic installations where the inner leaf is only 100mm thick? In the case of my kitchen, the inner blocks actually have an insulation filled cavity "within" the block itself. So the effect of chasing to 50mm depth (and into this cavity) is even more damaging.

Phil

[Dave Plowman (News)]

If those are truly the only options it makes me wonder what planet these 'legislators' are on.

A leakage operated device is often bad news for anything with certain types of heating elements

Proper steel conduit is expensive and requires skill and special tools to install.

Chasing two inches into the average wall for a whole cable run will likely weaken it.

[John Rumm]

4 Use a cable with integral earth shield (including SWA or MICC for example)

(1 would be the obvious choice in many cases)

Its not ideal in many if not most cases.

[BigWallop]

There are already products

have been around since cables were first buried under plaster. Cut your chase to brick depth and fix your cable. Place the metal capping over it with a few wide head nails at the edges (or drill and screw it), just to hold it in place until you make good the plaster work.

If you really want to fulfill every regulation in the book, then you can drill one end of the capping and fix an earth bond from it to the new socket / appliance point. But that is not absolutely needed. All you really want, is to stop anyone banging a nail through the cable, which the capping has already been designed to do.

And it's a lot cheaper in the long run, because you're not going to all the trouble of trying to fix the other options you talk about above.

Have a look in your local wholesaler for it.

[dennis]

that have been around since cables were first buried under plaster. Cut

No it isn't. Its just to stop the plaster's float damaging it. It offers *no* protection against nails or multi-construction drills. The plastic stuff is cheaper and does the same job.

Do tell him what its for, they like a laugh occasionally. ;-)

>

[Andy Burns]

4 Fix cable to wall using cable clips, so it will be unseen when the kitchen units are fitted, routing it to the isolation switch without being unsightly might be a challenge.

[TheScullster]

"Andy Burns" wrote

Having a solid floor means the cable is coming down from the ceiling, so unfortunately your suggestion is a non-starter.

Phil

[The Natural Philosopher]

Well maybe not.

I had a similar situation, although my walls were plasterboard over ply But one wall was distinctly 'bent' such that a worktop didnt really fit flush against it, and neither did the eye level cupboards..

The answer was to instal the cupboards and units with an ugly gap, and then I made a false wall between them with vertical battens and covered it in 12mm MDF. I was going to tile it, but painted it and its still that way.

cables run behind that..clipped to the wall behind.

All I lost was about an inch and a half of worktop.

[Mike Clarke]

But wouldn't that make them subject to the new 17th edition rules if the work was being done now?

[BigWallop]

> that have been around since cables were first buried under plaster. Cut

Am I missing the point? Sorry, but from what I am reading above, the cable needs protected down a wall, under the plaster. Unless you are a complete moron, that goes banging holes in walls with chisels and drills willy nilly into all parts of the building without checking first. Then a piece of cable capping is enough protection to stop a picture nail from being hammered through the cable.

In fact, if you are drilling into a wall, you would normally use a masonry bit in the pistol. A masonry bit is more likely to bend the capping before it breaks through, which, to a normal person, gives warning because of the sudden resistance against drill. We are talking about normal people, aren't we?

The capping is also better detected by devices meant to check the area you are about to drill into. No one said it protects the cabling from nuclear attack, but it does offer enough protection from someone banging a nail through it.

If the cable is in an area prone to damage through exposure to morons, then either fix it surface to make it completely obvious that the cable is where it is. Or fix it surface inside a trunk to make it obvious that things should not be bashed through it.

If you have a cable that needs full protection from all types of environments, then you would have to find a very special type of cable.

You could break through the inner skin and fish the cable through the cavity, under / behind the block / brick that you don't want to cut chunks out of.

But I thought we were talking normal. My apologies again.

I like to have a good relationship with my suppliers. :-)

[dennis]

The latest regulations require specific protection, the metal capping isn't it.

Do normal people use sds drills or multi-construction bits? Either will go through the metal capping without you noticing.

No it doesn't. Masonry nails are hardened steel and will just go straight through.

The new regs assume all areas are prone to damage.

Its not to protect the cable, its not expected to survive, however the person doing it is protected.

[Martin Carroll]

In article , TheScullster writes

Is this the case if the cable is in the "safe zone" (i.e. horizontally/vertically in line with switch)?

Martin

[Simon Stroud]

One good place I found for bringing an extra cable down from above in my kitchen was just behind one of the "decor end panels" on the upper cupboards. I just put it forward a little bit (may have trimmed a tiny bit off the rear but TBH don't remember doing that) and that creted a little channel that a (lighting) cable or two could slip down. Might be a bit of a squeeze for a fat 6mm2 or 10mm2 cable but it avoided doing anything drastic when I realised I needed a bit more under-cupboard lighting after nearly finishing the kitchen.

Regards, Simon.

[Mike Clarke]

I agree with Dennis there. A while ago I needed to re-route a length of old cable covered by metal capping under plaster. As I excavated plaster along it's length I could see it was heading ominously for a picture hook on the wall. Sure enough the pin for the hook had been hammered in straight through the metal capping and the cable. Subsequent examination of the cable showed that the pin went straight through the live conductor of the old 7/.029 T&E with 4 strands one side of the pin and three the other. The odd thing is that it had been like that for years without causing any trouble.

[The Medway Handyman]

I was thinking about those multi material drills, they will drill steel quite effectively - certainly would go through metal capping easily enough.

[BigWallop]

I thought we were talking about a cable that is being covered by wall units and probably tile between worktop and wall units. For a situation like that, then a cover to stop small picture nails is surely enough protection.

It's not a cable in the middle of a bare wall, where someone is going to come along and start banging holes through to put up shelves and the like. The wall units will be probably be covering most of the cable run, and the space exposed above the units will probably not have anything other than boxes or ornaments in it, on top of the kitchen units.

Or you could use this stuff

to really make sure the kitchen fitters don't have an accident. :-)

[Andy Wade]

There's guidance in the On-Site Guide about the maximum depth of chases. The depth of vertical chases shouldn't exceed one-third of the wall (leaf) thickness. For horizontal chases the max. depth is one-sixth of same.

Using a 30 mA RCBO is unlikely to give any problems if the cooker's in good condition (although actually fitting one in an older CU might). If you really want to use a non-protected circuit, the only practical options in most cases are:

- surface wiring, where acceptable;

- use a cable to BS 8436 - Earthshield or Flexishield (with these the OPD must be a Type B MCB meeting energy limiting class 3), or MICC cable if you have the skills to install it.

[Martin Carroll]

In article , TheScullster writes

Asked the question further down the thread but didn't get a reply!

Why does the cable have to be buried if it runs in the zone vertically or horizontally from the cooker switch?

Cheers

[Martin Carroll]

In article , Martin Carroll writes

What I meant to say was why should it be buried 50mm below surface?

Cheers

[John Rumm]

To circumvent the 17th edition requirement that concealed cables have "Additional protection" from a