Does SWA cable need to be earthed at both ends?

Yes. The steel wire armour of SWA cable must be connected to earth at both the supply end and the load end. SWA glands with an earth tag and locknut are used to clamp the armour and provide the earth connection at each termination point. Earthing the armour at both ends ensures earth fault protection across the full length of the cable run and satisfies the requirements of BS 7671 Regulation 543.

What is the minimum burial depth for SWA cable in the UK?

BS 7671 Regulation 522.8.10 requires buried cables to be at a sufficient depth to avoid damage from any reasonably foreseeable disturbance of the ground. The IET On-Site Guide gives practical guidance of 500mm under footpaths and garden areas, and 600mm under driveways and areas subject to vehicle loading, measured from the surface to the top of the cable. Regulation 522.8.10 also requires the cable location to be marked by cable covers or suitable marker tape. Cable route markers should be installed at the surface at regular intervals and at every change of direction.

Can SWA cable be used as the earth conductor?

The steel wire armour can be used as the circuit protective conductor (CPC/earth conductor) provided the armour cross-sectional area is sufficient to meet the requirements of BS 7671 Regulation 543. In many 3-core SWA installations, the armour carries the earth with separate line and neutral conductors inside. However, for installations where the armour CSA is insufficient, a separate earth conductor must be included or a 4-core cable used with one core dedicated to earth.

What type of gland is used for SWA cable?

SWA cable requires a specific armoured cable gland, commonly a "BW" or "CW" type brass gland with a cone and back-nut that grips the armour wires mechanically. The gland body clamps the armour to provide mechanical retention and earth continuity. An earth tag is fitted under the lock-nut to provide the earth connection to the enclosure. For outdoor and underground work, use IP66 or IP68 rated glands. For indoor dry locations, IP54 may be acceptable.

What size SWA cable do I need for a 100A supply?

For a 100A single-phase supply run underground (reference method D — buried direct in ground), 35mm² 2-core SWA is typically required. The exact cable size depends on the run length, voltage drop allowance (maximum 4% for final circuits under BS 7671 Appendix 4), installation method, grouping with other cables, and ambient ground temperature. Always carry out a full cable sizing calculation and check voltage drop for your specific installation. Elec-Mate's cable sizing calculator can assist with this.

Does SWA cable need additional protection in the ground?

SWA cable provides its own mechanical protection by virtue of the steel wire armour, so additional conduit or ducting is not generally required for burial. However, where the cable passes under roads, driveways, or through building walls, it is good practice to route it through a duct to allow future replacement without excavation. Where cables are buried in concrete or pass through corrosive soils, consult the cable manufacturer for additional protection requirements.

How do I strip SWA cable correctly?

Stripping SWA cable requires an armoured cable stripper or a sharp hacksaw and care to avoid nicking the inner insulation. Score around the outer sheath at the required strip length, bend the cable to crack the sheath, then cut back. Fan out the armour wires and cut them to the correct length for the gland using side cutters. Slide the gland body over the armour wires before applying the cone and back-nut. Never cut the armour wires too short — they must be gripped firmly by the gland cone.

INSTALLATION GUIDE

Armoured Cable Installation UK: SWA Cable Guide

Everything electricians need to know about Steel Wire Armoured (SWA) cable — core configurations, current ratings, correct gland termination for earth continuity, underground burial depths, IP ratings, and the common mistakes that generate EICR observations.

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12 min readUpdated 2026-06-10Andrew Moore, Founder of Elec-Mate

Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.

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Key Takeaways

1Steel Wire Armoured (SWA) cable is the standard for underground and external electrical installations in the UK, providing mechanical protection against accidental damage.
2The armour wires on SWA cable must be connected to earth at both ends of the run using appropriate SWA cable glands with a lock-nut and earth tag — the armour itself provides the circuit protective conductor.
3Buried SWA cable must be at a sufficient depth to avoid damage from any reasonably foreseeable disturbance of the ground (BS 7671 Reg 522.8.10). The IET On-Site Guide recommends 500mm under footpaths and 600mm under driveways as practical benchmarks. The cable location must be marked with cable covers or marker tape.
4Select the correct number of cores for the application: 2-core for single-phase with separate earth, 3-core for single-phase with armour earth, 4-core for three-phase.
5SWA cable glands must be rated to at least the same IP rating as the enclosure they terminate into. IP66 and IP68 glands are common for outdoor and underground work.
6Always fit the gland shroud over the cable before fitting the gland body — once the gland is tightened onto the enclosure the shroud cannot be fitted retrospectively.
7Voltage drop for SWA runs must be checked against the limits in BS 7671 Appendix 4, Section 6.4 (4% for final circuits, 3% for lighting). On site, apply a 0.8 correction factor to the Table 41.2 Zs limit to account for conductor temperature at the time of test.

01 · Installation Guide

What is Steel Wire Armoured (SWA) Cable?

Steel Wire Armoured (SWA) cable is a robust, multi-core power cable designed for fixed installation in situations where mechanical protection is required. It is the standard cable type for underground power runs, external installations between buildings, and industrial and commercial wiring where the cable may be exposed to accidental damage.

SWA cable comprises an inner conductor (copper or aluminium), XLPE or PVC insulation on each core, a bedding layer, a layer of galvanised steel wires wound helically around the cable (the armour), and an outer PVC sheath. The steel wire armour provides excellent mechanical protection and, crucially, provides the circuit protective conductor (earth) path for the installation when correctly terminated with appropriate glands.

Mechanical protection — the steel wire armour protects against physical damage from excavation equipment, rodents, and accidental impact.
Underground suitability — SWA cable is approved for direct burial in ground and does not generally require additional conduit protection.
Earth continuity — when correctly terminated, the armour wires provide a low-impedance earth path meeting BS 7671 requirements.

SWA cable must be installed in accordance with BS 7671:2018+A4:2026 (the IET Wiring Regulations). Cable sizing, burial depth, and termination requirements are all specified in BS 7671 and the associated IET Guidance Notes.

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02 · Installation Guide

Types and Core Configurations

SWA cable is available in several core configurations, each suited to different applications. Selecting the correct number of cores is essential to ensure the installation meets both functional and earthing requirements.

2-core SWA — line and neutral conductors only. Used for single-phase circuits where the armour itself provides the earth (circuit protective conductor). The armour must be connected to earth at both termination points. Common for sub-main feeds to outbuildings, garden offices, and garages.
3-core SWA — line, neutral, and earth conductors. The dedicated earth core allows a larger CPC cross-section than the armour alone may provide. Also used for three-phase delta circuits (three lines, no neutral) where the armour provides the earth.
4-core SWA — three line conductors and a neutral. The standard cable for three-phase and neutral (TN-S or TN-C-S) power distribution. The armour provides the earth. Used for feeding three-phase distribution boards, large machinery, and commercial sub-mains.
5-core SWA — three line conductors, neutral, and earth. Used where a separate dedicated earth core is required in addition to the armour earth, typically in TN-S systems with strict earth impedance requirements.

Conductor sizes range from 1.5mm² to 400mm² and above for large power cables. XLPE insulation is preferred over PVC for higher-temperature applications and improved current-carrying capacity. Aluminium conductor SWA (AWSWA) is used for large distribution cables where copper would be prohibitively heavy and expensive.

03 · Installation Guide

Current Ratings for SWA Cable

Current ratings for SWA cable depend on the installation method, number of circuits grouped together, ambient temperature, and conductor material. The following figures are approximate for copper conductor XLPE-insulated SWA cable buried directly in ground (reference method D, BS 7671 Appendix 4, Table 4D4A) at 15°C ground temperature:

4mm² 2-core — approximately 44A buried, 36A clipped direct. Suitable for ring final circuits and small sub-feeds.
10mm² 2-core — approximately 73A buried, 61A clipped direct. Suitable for cooker circuits and moderate sub-mains.
25mm² 4-core — approximately 130A buried. Common for three-phase sub-mains feeding distribution boards.
95mm² 4-core — approximately 265A buried. Used for large three-phase distribution feeds and main supplies.

Always apply correction factors for grouping (Ca), ambient temperature (Cg), and soil thermal resistivity before selecting cable size. Verify voltage drop does not exceed the limits in BS 7671 Appendix 4, Section 6.4 (4% for final circuits, 3% for lighting circuits from the origin of the installation). A cable sizing calculation should be documented and retained as part of the installation records.

04 · Installation Guide

Stripping and Terminating SWA Cable

Correct termination of SWA cable is critical for both mechanical security and earth continuity. The armour must be correctly dressed and gripped by the gland to maintain the earth path and prevent the cable pulling out under mechanical stress.

Step 1 — measure and mark — measure the depth of the gland entry plus additional length for the armour to be gripped. Mark the outer sheath with a knife or tape. Allow additional length inside the enclosure for core dressing and connection.
Step 2 — remove outer sheath — score around the outer PVC sheath with a sharp knife, taking care not to cut into the armour wires. Bend the cable to crack and remove the sheath section. Use an armoured cable stripping tool where available to avoid knife slips.
Step 3 — dress the armour — fan out and straighten the steel armour wires. Cut them square at the correct length using sharp side cutters. The armour wire tips should align consistently — uneven armour leads to poor gland grip and reduced earth continuity.
Step 4 — fit the shroud first — slide the plastic shroud over the cable before fitting the gland body. Once the gland is tightened onto the enclosure the shroud cannot be passed over it. This is the single most common SWA termination error in practice — a shroud omitted at this stage cannot be retrofitted without stripping the termination back.
Step 5 — fit the gland — slide the back-nut and cone over the armour wires (cone first, cone taper facing the gland body). Feed the cable through the gland body entry hole in the enclosure. Tighten the back-nut to draw the cone under the armour wires and clamp them firmly. Do not overtighten — the armour wires should be gripped firmly without being crushed or cut.
Step 6 — earth connection — fit an earth tag (lug) between the gland body and the enclosure lock-nut. Connect a green/yellow earth conductor from the earth tag to the enclosure earth bar. This provides the earth continuity between the armour and the installation earth.

After termination, verify earth continuity with a low-resistance ohmmeter from the armour at one end to the earth connection at the other. The earth loop impedance should be calculated and verified to be within the limits in BS 7671 Table 41.2 for the relevant protective device. On site, conductors are typically below their maximum operating temperature at the time of test, so apply a 0.8 correction factor to the Table 41.2 limit (equivalently, multiply your measured Zs by 1.25) before comparing to the tabulated value — this is the temperature-correction approach set out in GN3 and referenced by BS 7671 Regs 411.4.201–411.4.204 and Appendix 3.

05 · Installation Guide

Underground Burial Depth Requirements

Burial depth is a critical aspect of underground SWA cable installation. Insufficient depth increases the risk of accidental damage from digging, which can cause electrocution and fire. BS 7671 Regulation 522.8.10 requires buried cables to be at a sufficient depth to avoid damage from any reasonably foreseeable disturbance of the ground. The IET On-Site Guide gives practical guidance on appropriate depths for different ground conditions.

Footpaths and garden areas — IET On-Site Guide guidance indicates 500mm as a practical minimum for areas not subject to vehicle loading, measured from the finished ground level to the top of the cable.
Driveways, car parks, and roads — IET On-Site Guide guidance indicates 600mm as a practical minimum for areas subject to vehicle loading. The required depth may be greater where heavier loads or groundworks are foreseeable.
Warning tape — Regulation 522.8.10 requires the location of buried cables to be marked by cable covers or a suitable marker tape. Yellow/black cable warning tape should be laid above the cable for its full run length to warn anyone digging before they reach the cable.
Route markers — cable route marker posts or tiles should be installed at regular intervals (typically every 3m to 5m) and at every change of direction to allow the cable route to be traced at the surface.
Bedding — lay the cable on a layer of fine sand or selected fill free from sharp stones, glass, and debris. Cover with further selected fill before backfilling. The bedding depth should be appropriate to the cable diameter and ground conditions.

PME / TN-C-S earthing — outbuildings

When feeding a detached outbuilding via SWA on a PME (TN-C-S) supply, the SWA armour must not carry the PME combined neutral-earth (PEN) to the outbuilding. A PME earth that reaches a separate structure creates a shock risk if the neutral is lost elsewhere on the network. In this situation a local TT earth electrode must be installed at the outbuilding and the armour must not be used as the earthing conductor between the two buildings. Confirm the earthing arrangement with your DNO if in doubt.

Where it is not practical to achieve minimum burial depths (for example where the cable must cross a shallow area of bedrock), the cable must be provided with supplementary mechanical protection such as duct, tiles, or concrete encasement. Record cable routes on as-fitted drawings and retain these for the life of the installation.

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06 · Installation Guide

IP Ratings for SWA Glands

The IP (Ingress Protection) rating of SWA cable glands must be appropriate for the installation environment. A gland with insufficient IP rating will allow moisture and dust ingress that can cause premature failure of the termination and earth continuity issues.

IP54 — dust protected, splash-proof. Suitable for indoor installations in locations where dust or occasional water splash is possible (e.g., garages, plant rooms). Not suitable for outdoor or underground use.
IP66 — dust tight, powerful water jet proof. The standard minimum rating for outdoor glands and cable entry into outdoor enclosures. Suitable for surface-mounted external installations.
IP68 — dust tight, continuous submersion. Required for glands at underground cable entry points into pits, chambers, and below-ground enclosures. Also required where cables pass through below-ground walls.

The gland IP rating must match or exceed the IP rating of the enclosure. Where an IP68 gland enters an IP66 enclosure, the overall protection is limited to IP66. Ensure the correct gland seal (neoprene, EPDM, or silicone depending on temperature and chemical exposure) is selected for the application.

07 · Installation Guide

Common Mistakes in SWA Cable Installation

SWA cable installation errors frequently appear as observations on EICRs and can result in dangerous conditions if left uncorrected.

Armour not earthed at one or both ends — the most dangerous and most common mistake. An unearthed armour provides no fault protection and can become live if a conductor within the cable faults to the sheath.
Wrong gland type — using standard (non-armoured) cable glands on SWA cable. These grip only the outer sheath and provide no armour retention or earth continuity path.
Insufficient burial depth — cables buried too shallow are routinely damaged during garden work and landscaping. Always verify depth with a measurement and record it.
No route markers or warning tape — without markers, future groundworks will have no warning that a buried cable exists. Route markers are a BS 7671 requirement, not an optional extra.
Undersized cable for voltage drop — SWA cable runs are often long. Voltage drop must be calculated for the full run length and verified against the limits in BS 7671 Appendix 4, Section 6.4.

08 · Installation Guide

For Electricians: Documenting SWA Installations

Every SWA cable installation must be certified with an Electrical Installation Certificate (EIC) or Minor Electrical Installation Works Certificate (MEIWC) as appropriate. As-fitted cable route drawings and cable sizing calculations should be attached or retained.

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Reviewed by Andrew Moore, founder of Elec-Mate. Content is grounded in BS 7671:2018+A4:2026 and the IET Guidance Notes series.

Frequently Asked Questions About SWA Armoured Cable Installation

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Armoured Cable Installation UK: SWA Cable Guide

Key Takeaways

What is Steel Wire Armoured (SWA) Cable?

Get the BS 7671 A4:2026 Cheat Sheet — free

Types and Core Configurations

Current Ratings for SWA Cable

Stripping and Terminating SWA Cable

Underground Burial Depth Requirements

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IP Ratings for SWA Glands

Common Mistakes in SWA Cable Installation

For Electricians: Documenting SWA Installations

Certify on Site

Complete SWA installation certificates on your phone

Frequently Asked Questions About SWA Armoured Cable Installation

Does SWA cable need to be earthed at both ends?

What is the minimum burial depth for SWA cable in the UK?

Can SWA cable be used as the earth conductor?

What type of gland is used for SWA cable?

What size SWA cable do I need for a 100A supply?

Does SWA cable need additional protection in the ground?

How do I strip SWA cable correctly?

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