Thanks for that.

I have done the measurements (sheathing and conductor) and indeed it appears to be 4mm.

Sheathing is 11.9x6.25mm (snug) and it's multistrand cable at around .85mm in diameter per strand (or as near as I can measure it) which adds up to 2.87mm right? It may be slightly less as I didn't want to compress the bundle.

The sheathing also has the number '4' on it's own along the the 'Basec BS6004 (2006)' data.

To do this with stranded cable::

Unwrap the strands so you have just one strand
Measure the diameter of the single strand, halve it to get the radius
Work out the area of the single strand ( &#960;r² )
Multiply by the number of strands

A very rough way to ESTIMATE the CSA is to measure the outside of the cable sheath (with the insulation). There are guide figures and more info here

I would of course be getting an electrician in to check/test all circuits and have taken appropriate advice concerning cable routing/insulation gaps etc.
OK - so that's what you are going to do.

When you applied for Building Regulations approval, what did you say you were going to do? When they gave you approval, what did they think you were going to do?

it's multistrand cable at around .85mm in diameter per strand (or as near as I can measure it) which adds up to 2.87mm right?
Wrong.

How did you get from 0.85 to 2.87?

(7 x 0.85mm dia is 4mm², I'm just wondering what calculation you thought you were doing)

..

I would of course be getting an electrician in to check/test all circuits and have taken appropriate advice concerning cable routing/insulation gaps etc.
OK - so that's what you are going to do.

When you applied for Building Regulations approval, what did you say you were going to do? When they gave you approval, what did they think you were going to do?

The loft conversion company did all the structural work (eventually, after much to and fro) and roofing/cladding. I have done stud walls, insulation, floors, fire doors, windows etc.

The BC people have agreed that I can route the cables through prescribed voids built into the stud wall designs and have an electrician connect/test the installation with BC returning to inspect the cable and connection/certification on completion.

Basically I am doing the donkey work and routing the cable/chopping in the box holes etc, but that is the extent of it. My enquiries here are purely to determine the best points to tap in and begin the route.

it's multistrand cable at around .85mm in diameter per strand (or as near as I can measure it) which adds up to 2.87mm right?
Wrong.

How did you get from 0.85 to 2.87?

(7 x 0.85mm dia is 4mm², I'm just wondering what calculation you thought you were doing)

My fault. I interpreted the site instructions wrong (too eager at 7am I guess) and halved the figure.

The BC people have agreed that I can route the cables through prescribed voids built into the stud wall designs and have an electrician connect/test the installation with BC returning to inspect the cable and connection/certification on completion.
Fair enough.

Basically I am doing the donkey work and routing the cable/chopping in the box holes etc, but that is the extent of it. My enquiries here are purely to determine the best points to tap in and begin the route.
You really should be asking the electrician who you're expecting to inspect/test/certify....

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