Methods of mechanical protection for cables:
1. SWA (Steel Wire Armour) cable. This is by far the easiest option. This has steel wires running along the outside of the current-carrying cores. These steel wires are earthed at at least one end of the cable. So if someone shoves a spade through it, the spade will conduct very high current from the live cores to the earthed armour and trip the circuit breaker almost immediately, ensuring nobody gets hurt. It is also far better protected against impact. The ends of the cable are terminated in special glands, in order to earth the steel sheath properly.
2. Earthed metal conduit. This provides similar protection to SWA - it encloses the cable in an earthed metal layer. However, it is tougher than SWA, so you are less likely to put your spade through this. Much more difficult for DIYers to install - the ends need threads cutting and special tools are needed for this. It is also more expensive, especially when you’ve bought all the tools. Very rarely used to run underground installs. Most often used for industrial and commercial installs or in domestics where protection is required eg. garages, and run along walls outside.
3: MICC: thin, extremely long lasting and the bare coper variety blends nicely on bare brick walls. Some mechanical protection but not as much as SWA. However considered suitable for burial due to the protection afforded by its earthed metal layer BUT pricey and apparently difficult to terminate.
4: Split concentric: cheap and flexible and has the earthed metal layer making it considerd suitable for burial BUT prone to developing neutral to earth faults if pulled through rough ductwork etc. The recs (who don’t seem to give a damn about neutral-earth faults) make a fair bit of use of this stuff (and its relative plain concentric). Can be difficult to get especially in small sizes.
IF YOU USE THIS STUFF MAKE SURE YOU BUY COPPER SPLIT CONCENTRIC UNLESS YOU ARE FAMILIAR WITH THE SPECIAL TERMINATION PRACTICES FOR ALUMINIUM
5: Screened fire resistant cables (firetuff fp200 etc). A bit overkill for normal wiring but if you just need a short run outside of the zones in a wall and you wan’t something a bit smaller than you can get in split con this is worth considering.