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Cable type to use

Tolly

Hi,

A relatively minor issue but your thoughts will be appreciated.

An existing domestic installation is to have the internal service head moved to a new external meter box. A new 10m long 80-100A 1ph distribution cct will therefore be run from a switch fuse in the meter box (contentious, perhaps) to the CU.

The meter box will be approx 2-3 feet off the ground. The proposed cable route is to drill through the wall below the meter box up to approx a foot of the ground, that will go through into the basement.

The distr cct will be in the order of a 25mm2 cable. The issue is then the type of cable to use?

- A 3 core SWA will be difficult to use because its bending radius will be too great to get into the meter box; and drilling downwards to lessen the angle is inadvisable given water could track down the cable into the basement even after packing with sealant but which may deteriorate.

- Tails could be used, that are mechanically protected in e.g. conduit emanating from an adaptable box.

- Of interest though (due to not having used it before) is thoughts on using split-concentric in this scenario (which table F5 of GN 1 lists for general use) - given the short distance between the hole and the bottom of the box, perhaps it will be easier to bend up into box.

So thoughts please on using split-concentric.

Thanks.

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  • 0

    Can someone clarify about split concentric please. I`ve heard it said that we are not allowed to use split concentric.

    The reason, armoured cable must have all live conductors surrounded by an earth armour. Split con uses earth and also N for "armour".

    N is a Live conductor just the same as phase (or line) is. We are not allowed to use N as an armour.

  • 0 in reply to ebee

    You cannot meet BS7671 and use split con  in any situation where you should be  relying on earthed armour for protection - shallow buried in walls not following lines of least surprise, burial in places where it might be damaged unless in some suitably strong and obvious  duct etc, you need the armour,

    However, on the surface, so the route is visible or buried anywhere you might safely route or bury a non armoured cable  - and I agree that needs careful thought- you are OK, and rather like  this use of 5 core NYYJ  I mentioned a few weeks ago, it will always be unusual.

    Mike.

  • 0 in reply to mapj1

    So not barred as such in itself. Say you might use where you`d use clipped T & E for example but not where armouring is required. So not an everyday substitute for SWA like some seem to think it is?

    In so far as BS7671 is concerned. DNO have their own usages and rules of all sorts of things that might be alien in BS7671 land.

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  • 0 in reply to mapj1

    So not barred as such in itself. Say you might use where you`d use clipped T & E for example but not where armouring is required. So not an everyday substitute for SWA like some seem to think it is?

    In so far as BS7671 is concerned. DNO have their own usages and rules of all sorts of things that might be alien in BS7671 land.

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