Cable-runs buried in plaster

[Chris]

Having finally completed the re-wiring of the downstairs ring main in the house we have just moved to, I'm now left with the problem of the upstairs ring and downstairs and upstairs lights.

The problem is that the Consumer unit in under the stairs (split flight with 90 degree turn two thirds of the way up) and without completey wrecking the staircase there is no way I will ever get at the existing cable.

After a bit of lateral thinking it struck me that I could just take the three circuits under the downstairs boards and then up the brick work which is exposed in the lounge after ripping a partition wall out. This will then be subsequentally plastered. The cable runs (4 in all 2 x 1.0 for down and up lights and 2 x 2.5 for upstairs ring) would all be within 20cm from a corner.

Would I need to armour the cables at all, they wouldn't be very deep (15 to 20mm) from the surface of the wall when plastered.

Indeed would it be a good idea at all?

Thanks,

Chris

[Dave Liquorice]

Almost fine by the regs you only have 15cm from a corner or ceiling (*not* floor) in which you can bury cables without requiring proper protection (metal) or depth (>50mm).

Personally I'd cover them with plastic capping or oval conduit probably lights in one, ring in the other.

[Andy Hall]

You can do this without protection provided that the cables run vertically within 150mm of a corner.

Alternatively, they can run anywhere on the wall vertically provided that it is to and from a wiring accessory (e.g. switch or socket).

If it helps, you can run them horizontally within 150mm of the top of a wall but you can't run them horizontally near the floor in an equivalent band.

.andy

To email, substitute .nospam with .gl

[Chris]

Excellent, just the answers I wanted. That will save me a load of headaches.

Many thanks,

Chris

[Andy Wade]

No-one suggested that a grouping factor (Cg) check should be done to make sure that the current ratings will be OK.

Make sure that your four cables are arranged side-by-side on the wall in a single layer, preferably with some spacing between cables (which will help with plaster adhesion). The Cg for a single layer, cables touching, for 4 cables is 0.75, so the rating for the 2.5mm^2 comes down from 27A to just over 20A, which is OK, but only just - 20A is required. Similarly the 16A ungrouped rating for the 1mm^2 comes down from 16A to 12A - so OK for a 6 or

10A lighting circuit.

If the cables were to be bunched, the Cg would be 0.65 and that section of the ring circuit would have to be wired in 4mm^2.

Always consider grouping factors when installing more than one cable on a route.

[Chris]

They will be flat against the wall and not layered (I will probably clip them individually to the cement between the bricks). Could you please calrify, if they aren't touching (how much gap is required?) then is the Cg an issue?