SWA Armoured Cable: Glanding, Termination, and Underground Installation for UK Electricians

What Is SWA Cable?

Steel Wire Armoured (SWA) cable is the standard choice for permanent fixed-wiring installations in the UK that require mechanical protection — outbuildings, underground runs, garden circuits, commercial premises, plant rooms, and sub-main distribution. The armour layer provides physical robustness, and when bonded correctly at both ends, it also serves as a protective conductor (CPC).

SWA is manufactured to BS 5467 (XLPE-insulated) or BS 6346 (PVC-insulated). XLPE types handle higher operating temperatures (90 °C conductor, 250 °C short-circuit limit) and are now the predominant choice. Core colours follow BS 7671 harmonised conventions: brown (L), blue (N), green/yellow (E) for single-phase, and brown/black/grey/green-yellow for three-phase.

Where SWA Is Required

• Underground circuits — direct burial or in duct; armour withstands accidental impact and rodent attack
• Outbuilding supplies — garages, workshops, garden rooms, sheds: any detached structure fed from the main dwelling
• Sub-main distribution — consumer unit to sub-board runs in larger properties or commercial units
• EV charge point feeds — where the charge point is more than a few metres from the consumer unit (see EV Charging Installation Guide #54)
• Plant rooms, meter cupboards, and risers — where cables pass through areas with mechanical hazard
• Surface runs in commercial/industrial premises — where T&E would require conduit or trunking

SWA is not required for cables clipped to a wall inside a dwelling that are otherwise protected — T&E in plasterboard or behind cladding is acceptable there. See Electrical First Fix #77 for how cable routes are typically planned.

Selecting the Right SWA Cable

Core Count

• 2-core (L + N): single-phase circuits where the armour serves as CPC — most common for outbuilding feeds
• 3-core (L + N + E or L1/L2/L3): three-phase delta or where a separate earth core is required by design
• 4-core (L1/L2/L3 + N): three-phase and neutral; most common for three-phase sub-mains
• 5-core (L1/L2/L3 + N + E): three-phase TN-S or TT installations requiring separate CPC

Conductor Size

SWA conductor sizing follows BS 7671 Table 4D4A (flat/multicore cable clipped direct) or Table 4D4B (buried). Always apply correction factors for grouping, ambient temperature, and burial depth. See Cable Sizing Guide #90 for the methodology.

Common sizes for residential outbuilding and garden circuits:

These ratings are tabulated values before correction factors — always apply derating for installation method, grouping, and ambient temperature before specifying.

Underground Installation Depth and Protection

BS 7671 and the IET Wiring Regulations do not mandate a minimum burial depth for SWA, but the IET Guidance Note 1 and Electricity Safety, Quality and Continuity Regulations (ESQCR) provide practical guidance:

• Private garden/landscaping areas: 450 mm minimum cover is widely accepted industry practice
• Under driveways and roadways: 600 mm minimum (heavy mechanical protection zone)
• Under agricultural land or public roadways: 900 mm; consult DNO requirements

Marker tape: Yellow "Caution: Electric Cable Below" tape should be laid 150–200 mm above the cable to warn future excavators. Concrete cable covers or purpose-made duct are advisable under driveways.

Note on backfill: Avoid sharp stones in the immediate backfill; use sharp sand around the cable or a layer of sifted soil before general backfill.

Conduit vs Direct Burial

SWA can be direct-buried without conduit. Running SWA through conduit (HDPE or twinwall drainage pipe) provides additional protection and enables future cable replacement without excavation — recommended under patios, driveways, and anywhere future access will be difficult.

SWA Glands: Types and Selection

SWA glands clamp the armour mechanically and electrically, securing the cable to an enclosure and providing IP protection at the entry point. The main types are:

• Type A (unarmoured gland) — not suitable for SWA; do not use
• Type B (armoured, no seal) — clamps armour, no outer sheath sealing; use indoors
• Type BW (armoured with shroud) — the standard choice for most indoor SWA terminations in dry locations; brass body + plastic shroud
• Type CW (armoured, outer-seal, indoor) — clamps armour and seals outer sheath; preferred where dampness is possible
• Type E1W / E1FW (weatherproof/IP) — rated IP56/IP68; suitable for outdoor enclosures, meter cupboards exposed to weather

Gland selection depends on the cable OD (outer diameter), which varies by manufacturer and core count. Always check the gland manufacturer's cable OD chart — a 6mm² 2-core XLPE SWA may have an OD of around 14–16 mm depending on manufacturer, requiring a different gland range from a 16mm² cable at ~24 mm OD.

Gland kits typically include: gland body, clamping ring, locknut, earth tag, and shroud. A standard kit for a 2-core 6mm² cable will also include a brass earth continuity nut.

Terminating SWA Cable: Step-by-Step

Tools Required

• Armoured cable cutters or angle grinder with cutting disc
• SWA stripping tool (or sharp knife for experienced users)
• Wire strippers
• Hacksaw (fine tooth) for armour cutting
• Flat-blade and cross-head screwdrivers
• Spanner for locknut (typically 20–32 mm)
• Earth sleeving (green/yellow) to sleeve armour where it terminates on earth bar
• Multimeter or continuity tester for armour continuity verification post-termination

Procedure

1. Measure and mark: Allow sufficient cable to dress neatly inside the enclosure. Mark the outer sheath 50–80 mm back from the end — this is where the gland clamping ring will sit.
2. Remove outer sheath: Score around the circumference at your mark with a Stanley knife — do not cut through the armour. Peel back and cut off the outer sheath. A proprietary SWA stripper is far safer than a knife.
3. Prepare the armour: Count the individual steel wires. Using round-nosed pliers, carefully bend each steel wire backwards (away from the cable end) to loosen them. Cut the wires 30–40 mm from the edge of the outer sheath using wire snips — leaving a "cage" of wires that the gland body will clamp.
4. Assemble the gland (part 1): Thread the locknut and then the shroud (if BW type) over the cable BEFORE inserting into the enclosure knockout — a common mistake is forgetting this step. Fit the clamping ring onto the steel wires you folded back.
5. Install the gland body: Insert the gland body through the enclosure knockout from the outside. The front of the gland body should be flush with the inside face of the enclosure. Tighten the locknut with a spanner to clamp the gland securely.
6. Terminate the armour: Tighten the clamping ring on the gland body to grip the steel wires firmly. Pull the cable to verify the termination does not slip.
7. Fit the earth tag / earthing: Most gland kits provide a brass tag that fits under the locknut inside the enclosure. Run a short length of green/yellow sleeving over the armour connection tail and terminate on the earth bar inside the enclosure. For domestic installations, the earth tag wire is typically 4–6 mm² green/yellow.
8. Strip inner cores: Remove the inner bedding (PVC tape or filler) to expose the individual cores. Strip the insulation from each core to the length required for the termination (terminal block or bus bar spacing).
9. Fit core end sleeves and terminate: Fit bootlace ferrules if terminating in spring-cage or compression terminals. Connect brown to line, blue to neutral (or appropriate phase colours for three-phase), and green/yellow armour to earth.
10. Tighten gland shroud: Slide the shroud down and tighten onto the gland body. On CW-type glands, tighten the rear compression seal to grip the outer sheath and provide IP protection.

Earth Continuity of the Armour

The armour must be bonded at both ends of the cable — at the source enclosure and the load enclosure. A common error is bonding at one end only (typically the supply end), leaving the far-end armour floating. Both ends must terminate to earth bars. Verify armour continuity with a low-resistance ohmmeter before energisation.

For 2-core SWA where the armour IS the CPC, the armour resistance must be factored into the Zs (earth fault loop impedance) calculation. The resistance of the steel wire armour is significantly higher than copper — this affects both the fault current and disconnection time, and must be verified during installation testing.

Regulation 522.6 and Mechanical Protection Requirements

BS 7671 Regulation 522.6 requires cables concealed in walls or partitions to be mechanically protected unless they are installed at a defined depth or run vertically to accessories. SWA satisfies the mechanical protection requirement throughout its route, but at the point of entry to an enclosure it must be clamped with an appropriate gland — leaving an unglanded SWA entry hole is non-compliant and will fail an EICR inspection.

SWA at the Consumer Unit

Where SWA terminates at the main consumer unit for an outbuilding circuit, the following apply:

• The circuit must be protected by an RCBO (or RCD + MCB combination) — see RCDs and RCBOs #53 and Consumer Unit Replacement #24
• Where the outbuilding circuit passes outdoors, a 30 mA RCD is mandatory under BS 7671 Regulation 411.3.3 (TN system with buried cable) or 411.5.2 (TT systems)
• The armour earth must terminate on the main earth bar inside the consumer unit, not on a circuit earth terminal
• If the outbuilding has its own consumer unit, that sub-board must be earthed via the armour CPC back to the supply consumer unit — and the sub-board must also have main bonding if it has its own gas/water entry points

Outbuilding sub-boards supplying socket outlets must have all socket circuits protected by 30 mA RCDs. If serving a caravan hookup, a caravan pitch supply unit with integrated RCD is required.

Part P Notification

A new circuit from the consumer unit to an outbuilding is notifiable work under Part P unless carried out by a registered competent person (NICEIC, NAPIT, ELECSA). The outbuilding sub-board, any new consumer unit, and associated earthing work are all notifiable. See Part P Building Regulations #162 for the full scope.

Common Faults and Inspection Points

• Armour not bonded at far end: Earth fault loop impedance test fails at the load end; armour may be live under fault conditions. Bond both ends.
• Cable too tight at entry: SWA under tension at a gland can crack the outer sheath where it exits the gland — allow a drip loop outside the enclosure for cables entering from below.
• Wrong gland type: Using a plain-entry gland (Type A) on SWA gives no mechanical protection to the armour at the termination point — fail on inspection.
• Steel wire armour cut too short: If the wires are trimmed flush to the outer sheath, the gland clamping ring has nothing to grip — the cable can be pulled free under tension. Leave 30–40 mm of folded wires.
• Burial depth insufficient: Cable at <300 mm depth under a domestic garden is at risk; add duct or marker tape and record on the installation certificate.
• No installation drawings: BS 7671 requires an as-fitted cable route drawing for buried cables. Photograph the run before backfilling and include with the Electrical Installation Certificate.

Get It from APM Electricals

APM Electricals, 24 Western Avenue, Acton, London W3 7TZ. Call 020 8702 8080 or visit www.apmi.uk for same-day trade counter collection and next-day delivery across London and the UK.