Is Prysmian LSX a suitable replacement for armoured cable

You do have to be careful with selection of breakers if you have high prospective fault current. They must be used with an mcb or RCBO having an overcurrent characteristic classificationType B; in addition, the max I²t for 1.0 and 1.5 mm² csa cables to this standard is 42,000 A²s, and for 2.5 mm² and 4.0 mm² is 60,000 A²s.

AJJewsbury said:

Originally it was only readily available to BS up to 4mm2

Yes, the current BS 8436 only specifies 1.0, 1.5, 2.5 and 4.0 mm² csa cables.

Alan B said:

Cleavland have CSX that goes up to 10mm

Sizes above 4.0 mm² are outside the scope of the current version of BS 8436. The CSX datasheet confirms this, that csa 6.0 mm² and 10 mm² cables are only available to IS 273. I don't have IS 273 immediately to hand to assist with installation conditions and selection of breaker for cables to that, unfortunately.

In terms of the question 'is it a suitable replacement for an SWA cable' BS 8436 does have limitations on where the cables are intended to be installed, stating (Clause A.1):

The cables specified in this British Standard are intended for installation in air (including installation in trunking or other closed systems), and in thin partitions and building voids when connected to a suitably selected protective device (see Clause 12). When cables are to be installed in any other environment, reference should be made to the cable manufacturer.

So, not plastered in a block/brick wall, for example.

gkenyon said:

So, not plastered in a block/brick wall, for example.

That's a nuance which isn't always made clear or is inconsistent between manufacturers, some manufacturers datasheets omit any reference to this, for example:

"APPLICATION: Screened cable for use in walls, partitions and building voids where there is a risk of damage or penetration from nails, screw fixings etc."

Nothing there to suggest any important subtleties around being suitable for use concealed within a wall, but only a specific type of wall. 

And when you step back and think of the engineering, what is the engineering logic behind the distinction between two identical cables, one behind a piece of plasterboard in a void, one behind a piece of plasterboard mounted on a block wall. Same cable, same route, cables could be secured in position, same distance from surface, similar degrees of support.  

TurboGen said:

And when you step back and think of the engineering, what is the engineering logic behind the distinction between two identical cables, one behind a piece of plasterboard in a void, one behind a piece of plasterboard mounted on a block wall. Same cable, same route, cables could be secured in position, same distance from surface, similar degrees of support. 

That sort of wall may be acceptable, but if the plaster is applied direct to the bricks/blocks, the cable may be immersed in the plaster and accordingly, liable to chemical attack.

Chris Pearson said:

That sort of wall may be acceptable, but if the plaster is applied direct to the bricks/blocks, the cable may be immersed in the plaster and accordingly, liable to chemical attack.

Again, what's the engineering logic here? The cable is covered by a continuous LSZH outer sheath, which provides a barrier between the aluminum film and anything external to the cable such as plaster, we use LSZH sheaths on other cables, like twin and earth, which are routinely immersed in plaster.

Even in a thin partition walls, plaster can be used around backboxes to bond them and incoming cables securely in position, so that is not a guarantee the cable won't be immersed in or exposed to plaster.

If plaster exposure is the engineering justification, then the prohibition on use on brick/block walls would be a poor way to protect against that, the obvious way is a clear stipulation - "this cable should not be used in contact with plaster or concrete." But that seems unlikely.

Agreed!

TurboGen said:

Again, what's the engineering logic here?

Water and soluble compounds in the plaster mix being deposited inside the construction of the cable.

Most cables are not fully "waterproof". It depends how long the plaster will take to dry, as to whether any ionic or other soluble compounds will be deposited within the cable itself.

TurboGen said:

Again, what's the engineering logic here?

Water and soluble compounds in the plaster mix being deposited inside the construction of the cable.

Most cables are not fully "waterproof". It depends how long the plaster will take to dry, as to whether any ionic or other soluble compounds will be deposited within the cable itself.