Cable Types & Selection FAQ

Use SWA cable when mechanical protection is needed: direct burial, outdoor installations, industrial environments with risk of impact or abrasion, and cable routes across open ground. The steel wire armour provides crush resistance, tensile strength, and can serve as the circuit protective conductor. SWA cable requires proper gland selection to maintain the armour’s earth continuity and IP rating at terminations.

LSOH cables use insulation and sheath materials that produce minimal smoke and no halogen gases when burned. Halogen gases combine with moisture to form corrosive acids that damage equipment and are toxic to people. LSOH cables are mandatory in enclosed public spaces, underground stations, hospitals, and high-rise buildings where smoke density and toxicity during fire must be minimised.

Fire alarm circuits require enhanced fire resistance to maintain circuit integrity during a fire. Options include mineral insulated cable (MICC), which maintains integrity above 1,000°C, or enhanced fire-resistant cables to BS 7846 (2 hours fire resistance). Standard PVC or XLPE cables fail rapidly in fire conditions. The cable must also resist water from fire-fighting operations.

Flexible cables with stranded conductors are not generally suitable for permanent fixed wiring because their insulation ratings and fire performance may not meet requirements. BS 7671 permits flexible cables for final connections to equipment, pendants, and appliance connections, but fixed wiring should use cables designed for permanent installation with appropriate mechanical protection and insulation class.

Single-core cables contain one conductor — used for large sizes where multicore would be impractical, or where trefoil or flat formation is needed for specific installation methods. Multicore cables contain multiple insulated conductors in a common sheath — convenient for installation as all phase, neutral, and earth conductors are in one cable. Single-core AC cables can experience induced eddy currents in steel enclosures.

Underground cables must be suitable for direct burial or duct installation. Use SWA (steel wire armoured) cables for direct burial with appropriate mechanical protection. Specify insulation rated for ground temperature and soil moisture conditions. Consider soil thermal resistivity for ampacity calculations. Install at minimum 500mm depth with protective tiles or warning tape, and use cable route markers at regular intervals.

BS 6004 Type B cable has a thicker sheath than Type A, providing enhanced mechanical protection for surface-mounted or partially protected installations. Type A (thinner sheath) is suitable for installations in conduit or trunking where the enclosure provides mechanical protection. Both types are available in flat twin-and-earth and three-core-and-earth configurations commonly used in domestic and commercial fixed wiring.

Data centre power cables should be LSOH for fire safety, XLPE insulated for higher current capacity in warm environments, and appropriately sized for continuous duty. Raised floor environments require plenum-rated cables. For redundant power paths, consider mineral insulated cables for critical feeds. Cable management must maintain separation between redundant supplies and between power and data cables.

Cable designation codes follow a standard pattern. For example, BS 5467 SWA cable: the first letters indicate conductor material (C for copper, A for aluminium), followed by insulation type (X for XLPE, V for PVC), armour type (WA for wire armour), and sheath material (S for LSOH). The numerical rating (e.g., 600/1000V) indicates phase-to-earth/phase-to-phase voltage.