Installation zones for concealed cables

[Andy Hall]

I am looking at BS7671 and various commentary books.

It is clear about the 150mm wide acceptable zones near corners and tops of walls.

It is also clear about vertical and horizontal runs from wiring accessories.

However, on one point, I can't see anything specific.

Consider this case:

- Wiring accessory has horizontal cable run which reaches corner

- On the adjoining wall at the same height, there is another wiring accessory.

- SInce it is permissible to run a cable horizontally from a wiring accessory, nothing is violated.

Now consider this case:

- Wiring accessory has horizontal cable which reaches corner.

- This time there is not a wiring accessory on the adjoining wall but after a second corner there is.

- The horizontal runs from each wiring accessory to the nearest corner is OK.

However, what about the middle wall?

Common sense would suggest that running the cable horizontally across the middle wall is not allowed because there is not a wiring accessory there.

However, the standard does not appear to be specific on this point.

The only thing I can see is that the opening words of 526-06-06 say

" When a cable is installed in a wall..."

which does suggest a wall by wall view of it, but the point isn't very explicit.

Comments?

[Bob Eager]

It may not be specific, but it would be best to adhere to the principle of least astonishment!

[Roger]

The message from Andy Hall contains these words:

I think you have put your finger on it with "When a cable is installed in a wall...". You would have to be at least as devious as John Cartmell to argue that 2 adjacent walls were really one just because they were contiguous.

One way round your problem would be to put in an unnecessary point on the middle wall.

I have a ring main running round my kitchen with outlets on 3 walls but that has to go up to the ceiling (into the void in my case) to get round a window. One of these days I really must get round to putting up the ceiling and plastering the walls but I am still undecided on how to insulate the walls. ;-(

[Andy Wade]

You do have the current (brown) edition? The wording of 522-06-06 was changed in the most recent amendment[*] and all of 522-06-07 was deleted.

[*] Amendment no. 2, AMD14905 - the one which, primarily, introduced the new wiring colours.

522-06-06 doesn't refer to "corners" but to "an angle formed by two adjoining wall or partitions." /Ipso facto/ ISTM that the intent is that each wall is to be considered separately.

Now if you have curved walls and/or rounded corners the interpretation could be more interesting...

[Andy Hall]

This was the blue one. I should get a brown one, I suppose.

Are there many other significant changes?

Exactly, and these are increasingly common.

I've decided to run cables to the corners then up in the 150mm space, along in the 150mm space near the ceiling and down again.

The other case, which is not covered is where the wall meets the ceiling at an angle - e.g. in loft rooms. For this one, I think that the reasonable interpretation is to have the 150mm zone following the angle with the ceiling.

[Andy Wade]

I'd wait. The 17th Edition is due out early in 2008.

Download the update from

The other case, which is not covered is where the wall meets the ceiling

This came up in another thread recently. I agree, it's a 150 mm wide zone from the top of the wall and there's nothing that says that the top, or the zone, has to be horizontal.

[John Rumm]

That would have been my take on the best way to do it.