Cables in plastic conduits

[Me]

Hi

I think that the regs indicate the cables in walls need to be protected against physical damage (e.g. hammering nails into the wall). I think that unless the cable is over

50mm deep in the wall or within 150mm of the edge of the wall that mechanical protection is needed. Fair enough.

But in my house, re-wired in 1982, all the cables in the walls are less than

50mm deep and in plastic oval conduit. If I'm extending the wiring, can I legitimately carry on with this scheme, or need I install metal shielding?

Regards John

[Andy Hall]

physical damage

50mm deep in the

needed. Fair enough.

50mm deep and in

The Wiring Regulations do allow you to run cables concealed without either the 50mm depth or steel protection either vertically or horizontally from wiring accessories - i.e. light switches and power sockets etc.

You only need the depth or protection if you want to run them at an angle or in other places - e.g. if you went horizontally from a switch and then up without there being a wiring accessory at the point where the cable changes direction.

There are also bands at the corners of walls as you say. To be precise they are 150mm wide in corners (along each wall) and 150mm from the top of a wall. The band at skirting board level for 150mm is not a permitted zone from this perspective.

.andy

To email, substitute .nospam with .gl

[Dave Liquorice]

Not quite. You don't need an accessory at the point of direction change provided that that point is at the intersection of vertical/horizontal lines from accessories.

eg

-----A-----+----- -----+-----B-----

You can cable between A and B via either route through the + points.

[Andy Hall]

The OSG and Whitfield illustrate and seem to say that a direction change without an accessory can only happen if the point of direction change is within one of the corner or top of wall 150mm bands; not even where a cable goes down vertically from an accessory to the floor.

.andy

To email, substitute .nospam with .gl

[Andy Wade]

BS 7671 itself says: "Where the cable is connected to a point, accessory or switchgear on the wall or partition, the cable may be installed outside these zones[*] /only in a straight run/ either horizontally or vertically to the point accessory or switchgear. [My emphasis]

[*] Meaning the zones within 150 mm of corners or the top of the wall.

That does seem to exclude Dave's interpretation, since that would require two straight runs. Whether or not this is what the original authors intended is a moot point. If you regard horizontal and vertical strips running the full width and height of the wall from every accessory as 'no go' zones for inserting fixings, then Dave's interpretation introduces no further risk of damaging a cable.

BTW - to the OP - these requirements were introduced in the 1987 amendment to the 15th edition and were effective from 12th June '87. Therefore your house, rewired in '82, may not comply.

[Me]

thanks, folks!

[Dave Plowman]

I don't think plastic conduit would offer any protection from nails - especially fine sharp ones like for picture hanging.

[Dave Liquorice]

It does indeed.

Which, IMHO, you have to do as you have no idea from looking at an accessory which of the four possible directions are in use for buried cables. OK you can take the accessory off and assume(*) that any sides that don't have a cable leaving them are safe. If you do that with my interpretation you are still "safe" though.

(*) As we all know "assume" makes an ASS out of U and ME.