Introduction – Underground Armoured Cable Installation
Table of contents
Underground armoured cable installation is the safest way to deliver power to outbuildings, gardens, and external equipment. By following the requirements of BS 7671 (IET Wiring Regulations), you can ensure buried SWA cable remains safe, compliant, and long-lasting.
At Electrical4Less, we supply underground armoured cables from Doncaster Cables and UK Cables, both trusted UK manufacturers.
Why Use Armoured Cable Underground?
Underground cables are chosen because the steel wire armour provides mechanical protection against:
- Spade strikes during excavation
- Crushing under driveways and patios
- Rodent damage
- General wear in harsh ground conditions
Unlike twin & earth, SWA complies with BS 7671 Regulation 522.8.10, which requires adequate protection when buried in the ground.
Technical Specifications of SWA Cables
Steel wire armoured cables are built to British Standards to ensure long service life underground. Typical specifications include:
- Voltage rating: 600/1000 V (to BS 5467 & BS 6724)
- Temperature rating: -15°C to +90°C continuous operation
- Conductor sizes: from 1.5 mm² up to 95 mm² and beyond
- Core counts: 2, 3, 4, 5, and 7 cores available
- Sheath materials:
- PVC (BS 5467) – durable, cost-effective, chemical resistant
- LSZH (BS 6724) – low smoke, zero halogen, safer in fire conditions
The construction ensures compliance with BS 7671 Appendix 4, which defines current-carrying capacity for cables installed underground or in ducts.
Mechanical Performance
SWA cables are tested to withstand demanding site conditions:
- Impact resistance: Withstands 6 Joules (equivalent to heavy blows)
- Compression resistance: Class 4, tested up to 1250 N
- Tensile strength: Galvanised steel armour provides additional pull strength during installation
- UV protection: Outer sheath resists sunlight when cables emerge above ground
These mechanical properties are why SWA remains the standard for buried installations.
Burial Depth and BS 7671 Guidance
BS 7671 Regulation 522.8.10 states that underground cables should be:
- Buried at 450–600 mm in domestic gardens, deeper in agricultural or public land
- Laid on a bed of sand or fine soil to prevent sheath damage
- Covered with marker tape before backfilling
- Protected with conduit or ducting if installed under driveways or high-traffic areas
Following these practices ensures compliance with Regulation 522.6.204 on mechanical protection.
Choosing the Right SWA for Underground Use
- PVC SWA – best for general-purpose outdoor runs, cost-effective and robust.
- LSZH SWA – required where low smoke and halogen-free performance is critical (schools, tunnels, public access areas).
Available options include:
- 2 Core LSZH SWA
- 3 Core PVC SWA | 3 Core LSZH SWA
- 4 Core PVC SWA | 4 Core LSZH SWA
- 5 Core PVC SWA | 5 Core LSZH SWA
Essential Accessories for Underground SWA
Compliance with BS 7671 Section 526 requires safe terminations:
- Armoured Cable Glands – maintain earth continuity and mechanical strength
- SWA Gland Banjos – provide earthing bonds
- SWA Clips – secure cables where they emerge above ground
FAQs – Underground Armoured Cable Installation
What current can SWA carry underground?
Depends on conductor size and burial method. Refer to BS 7671 Appendix 4 Table 4E4A for current-carrying capacities.
Do I need to earth the armour?
Yes, unless otherwise designed under BS 7671 Section 543.
Can SWA be joined underground?
Yes, using resin or heat-shrink joint kits, provided they meet BS 7671 Reg 526.5 (maintenance of integrity of connections).
How long does SWA last underground?
Typically 30–40 years if installed correctly, as long as sheath integrity is maintained.
Can I run SWA straight into a consumer unit?
Yes, using the correct armoured cable glands to terminate safely.
Should SWA be in ducting?
Not always. Ducting is used when extra protection is needed (e.g. beneath driveways).
Why Buy Underground SWA from Electrical4Less
At Electrical4Less we provide:
- SWA cables from Doncaster Cables and UK Cables
- PVC SWA and LSZH SWA
- Accessories including Armoured Cable Glands, SWA Gland Banjos, and SWA Clips
We’re trusted by electricians nationwide for fast delivery and reliable stock.
Underground Armoured Cable Installation – Best Practices for Compliance