SWA Cable Glanding: Gland Selection and Earthing

Summary

SWA cable terminations look straightforward — strip back, slide on the gland, tighten — but a bad termination is one of the more dangerous defects you can leave on site. The armour is the protective conductor on most SWA installations; if the gland is not seated properly, or the armour is not gripped, the earth path is broken and the cable becomes a buried hazard that only shows itself when there's a fault. Worse, a poorly sealed outdoor gland lets water track down the inside of the armour into the enclosure, and what looks like a switchgear failure turns out to be a £15 termination done wrong five years earlier.

The IET Wiring Regulations (BS 7671) are explicit on earth continuity, mechanical retention, and external protection at SWA terminations. The detail comes from manufacturer documentation (CMP, Hawke, Prysmian Cleveland), the IET On-Site Guide, and BS EN 62444 for the glands themselves. None of this is exotic; what catches people out is treating SWA glanding as a "muscle memory" job rather than reading the requirements for the specific installation conditions — wet, dry, hazardous, vibrating.

This article covers: gland type selection, sizing, the right tools, the correct stripping geometry, banjo and earth-tag practice, sealing at the enclosure face, when armour is acceptable as CPC and when it isn't, and the most common termination mistakes that lead to failures.

Key Facts

• Primary wiring standard — BS 7671:2018+A2:2022 (the IET Wiring Regulations, 18th Edition, with Amendment 2)
• Gland standard — BS EN 62444:2013 (Cable glands for electrical installations); superseded BS 6121
• Gland types — Type A/E1W (indoor seal), Type BW (indoor, no seal), Type CW (outdoor/damp, with inner + outer seal), Type E1FW/E1FX (hazardous area)
• Armour as CPC (BS 7671 543.1.3) — Acceptable only where the armour CSA satisfies the adiabatic equation S² = I²t / k² for the worst-case earth fault current and disconnection time
• Common armour CSA shortfall — 2.5mm² 3-core SWA armour equates to ~16mm² Cu equivalent; 4mm² and above usually meet 1.0 ratio adiabatic
• Mandatory earth tag/banjo — Bond armour at the gland to the local CPC via a tag washer (banjo) when armour is used as CPC; this provides the low-impedance path from the armour into the enclosure earth bar
• Stripping length — Cone-to-armour overlap typically 6–10mm; the rule is "armour just past the cone shoulder, not into the throat of the gland"
• Sealing washer — Always between the gland body and the enclosure face on outdoor or damp installations (PVC or neoprene); never substitute a fibre indoor washer for an outdoor one
• Locknut + entry thread — Brass locknut inside the enclosure; thread should be ISO metric (M20, M25, M32) for new work; older NPT/PG threads still found on legacy gear
• IP rating — Achieved IP rating is determined by the gland, the seal, and the enclosure entry, not just the gland alone
• Glass-reinforced nylon glands — Rarely acceptable for SWA armour grip; brass remains the default
• Multicore SWA cores — Identified per BS 7671 Table 51 (brown/black/grey for 3-phase, brown for single-phase L, blue N, green/yellow Earth on cables that have a dedicated CPC core)
• Older SWA core colours — Pre-2006 multicore used red/yellow/blue (3-phase). Mark with appropriate sleeves at termination

Quick Reference Table

Detailed Guidance

Choosing the Gland

Gland selection is a decision about three things: the cable (armour type, size), the environment (dry, damp, outdoor, hazardous), and the enclosure (thread, material, IP rating required).

For 99% of UK domestic and commercial SWA work — supplies to outbuildings, garden offices, garages, sub-mains to extensions — type CW with outer rubber/PVC washer and protective shroud is the default. Cheaper indoor BW glands save £2–£3 per cable but fail outdoors within a few years; do not use them where any moisture is possible.

For hazardous areas (petrol stations, paint shops, certain industrial), the gland must be ATEX/UKCA certified for the zone (Zone 1, Zone 2 etc.) and the gland selection is dictated by the equipment certification, not by the cable. This is specialist work — competent person status under the relevant scheme is required.

The Stripping Geometry

Most failed terminations are caused by getting the stripping geometry wrong. The aim is:

• The outer PVC sheath strips back just enough to expose the armour, with the sheath ending inside the gland body — not visible past the gland
• The armour ends just past the cone shoulder, gripped between the cone and the brass body — visible armour past the cone is too long; armour stopping short of the cone gives no grip
• The inner sheath continues inside the gland into the enclosure, with 25–50mm of inner sheath visible past the gland inside the enclosure to act as a sleeve where the cores break out
• Cores extend inside the enclosure, with green/yellow sleeve on any core repurposed as earth, and sleeves on cores reused as N (blue) or L (brown)

Get the geometry wrong and one of three things happens: the cone doesn't grip the armour (no earth continuity), the outer sheath sits inside the cable side rather than the enclosure side of the gland (the gland body's grip on the sheath is lost), or the inner cores are stretched against the gland body and chafe (insulation damage and live-to-earth fault risk).

Earthing — The Critical Bit

When SWA armour is used as the CPC, the gland must provide a verified path from the armour to the enclosure earth bar. Two methods:

1. Earth tag (banjo) washer. A brass washer with a tail or tag is fitted between the gland body and the enclosure outer face, with a green/yellow conductor clamped under the tag terminating at the earth bar inside the enclosure. This is the standard for cast iron enclosures, plastic enclosures, and any enclosure where the body is not itself a reliable earth path.
2. Direct metal-to-metal. For a galvanised steel enclosure with a substantial brass gland through a clean, paint-free entry point, the gland body itself bonds to the enclosure. Inside the enclosure, an internal locknut secures the gland and a separate earth conductor from a stud or tapped hole goes to the earth bar.

Use the banjo method as a default — it removes the assumption that the enclosure body is part of the earth path. Test on completion with an R1+R2 measurement (or armour-to-earth-bar continuity test); the result should be a small fraction of an ohm.

When Armour Cannot Be the CPC

The adiabatic equation in BS 7671 regulation 543.1.3 sets the minimum CPC cross-section for the earth fault current and disconnection time of the protective device. Some small SWA cables have armour that does not meet this when feeding a large protective device. Two examples:

• 1.5mm² 2-core SWA fed from a 32A MCB on a TT supply: the armour may not meet the adiabatic requirement at the achievable Zs.
• 2.5mm² 3-core SWA on a long run with a 40A device: similar issue.

In these cases, either uprate the cable (3-core to 4-core with one core as a dedicated CPC), reduce the protective device rating, or run a separate parallel earth conductor — all options are valid. Don't just terminate and hope; the lifetime of the installation may be 30+ years.

Use the manufacturer's published armour-as-CPC equivalent areas (e.g. Prysmian's data sheets) as the source for the calculation; treat second-hand "rules of thumb" with suspicion.

Sealing and IP Rating

The achieved IP rating at the enclosure entry depends on the whole assembly: gland with seal, washer to enclosure, locknut, shroud. A gland marketed as "IP66" achieves that only when fitted with the correct shroud and washer onto a matching enclosure entry — not as a bare gland.

For outdoor SWA terminations:

• PVC or neoprene sealing washer between gland body and enclosure outer face
• Brass locknut inside, tightened against the inner face
• Heat-shrunk or moulded shroud over the body of the gland to protect the seal from UV
• Optionally, a dab of glanding compound (gel) on the threads — not a substitute for the washer

The most common defect on outdoor terminations 5+ years old is a perished washer letting water track down the threads. When you find it, replace the washer — don't just retighten the locknut.

Termination Procedure (Standard Indoor/Outdoor CW Gland)

1. Cut cable to length, allowing 100–150mm extra for stripping and re-trims
2. Mark outer sheath strip length (typically 60–80mm depending on gland size)
3. Ring-cut and lengthwise-cut the outer sheath; remove
4. Mark armour cut length (typically 10–15mm shorter than outer sheath strip)
5. Cut armour cleanly at 90° with armour cutter or careful hacksaw work
6. Lightly file armour ends to remove burrs
7. Slide outer nut, locknut, washer onto cable (in that order — easy to forget the washer)
8. Slide cone over armour, ensuring all armour wires are above the cone (none caught underneath)
9. Strip inner sheath, leaving 25–50mm sheath inside the enclosure beyond the gland
10. Sleeve and identify cores per BS 7671 Table 51
11. Thread gland body through the enclosure entry, fit banjo earth tag if used
12. Tighten outer nut against gland body with two-spanner method
13. Verify armour grip by trying to pull the cable out — should not move
14. Tighten locknut inside enclosure
15. Connect cores to terminals and the earth/banjo tag to the earth bar
16. Test continuity from armour to earth bar
17. Insulation test, polarity test, all per BS 7671 Part 6

Tools

• Outer sheath stripper (rotary, e.g. Knipex 90 25 16) or sharp utility knife
• Armour cutter (Jokari Cabletool or equivalent)
• Two adjustable spanners or correctly sized box spanners for the gland
• Continuity tester (low-resistance ohmmeter to BS 7671)
• Insulation resistance tester (250V/500V/1000V)
• Sleeving in green/yellow, blue, brown for core identification
• Glanding compound (optional, manufacturer specific)

Frequently Asked Questions

Do I need a banjo earth tag for every SWA termination?

Use a banjo as a default best practice. Where the enclosure is plastic, always — there is no other earth path. Where the enclosure is metal but painted, always — paint is an insulator and the gland body cannot rely on enclosure contact. Where the enclosure is a bare, clean galvanised or stainless surface, the gland body itself bonds via the locknut, and a banjo is technically optional but commonly fitted as belt-and-braces.

Can I use SWA armour as the only earth on a TT supply?

Only where the adiabatic equation in regulation 543.1.3 confirms the armour CSA is adequate for the earth fault current and disconnection time at the achievable Zs. On a typical 100Ω earth electrode TT supply with a 100mA delayed RCD, the disconnection times are long enough that armour is usually adequate for most cable sizes — but always verify with a calculation, never assume.

What size gland for a 6mm² 4-core SWA?

Typically a 20S or 25 metric gland depending on manufacturer; the exact size is on the cable data sheet. Cable construction varies between manufacturers — a 6mm² 4-core from CMP isn't the same overall diameter as the same size from Prysmian — so order the gland for the specific cable, not from a generic table.

Is the armour the same as the bond between metallic services?

No. Main protective bonding (BS 7671 regulation 411.3.1.2) is a separate requirement from circuit CPC. The armour is part of the circuit protective system; it does not replace the main bonding from the MET (Main Earthing Terminal) to incoming gas, water, and oil services.

Why do my gland terminations work loose over time?

Three usual causes: (1) outer nut not tightened with two-spanner method — one-spanner-only can cause the gland body to rotate inside the enclosure rather than tightening against it; (2) cable is unsupported and pulling on the gland from cable weight — fit cleats/clips within 150mm of the entry; (3) thermal cycling on a high-load cable can loosen brass-on-brass joints — re-check on commissioning and at first periodic inspection.

Regulations & Standards

• BS 7671:2018+A2:2022 — IET Wiring Regulations (the foundation document)

• BS EN 62444:2013 — Cable glands for electrical installations (formerly BS 6121)

• BS EN 60079-14 — Explosive atmospheres — Electrical installations design, selection and erection (for hazardous-area glanding)

• BS EN 60529:1992+A2:2013 — Degrees of protection provided by enclosures (IP code)

• BS EN 50525 — Electric cables — Low voltage energy cables (the family standard for SWA cable manufacture)

• IET On-Site Guide (BS 7671 companion) — Practical guidance and tables for routine work

• IET Guidance Note 1 — Selection and Erection of Equipment (more detail on SWA application)

• IET Wiring Regulations on BSI — BS 7671 full text

• CMP Glands technical documentation — Major UK gland manufacturer

• Hawke Cable Glands — Manufacturer technical guide

• Prysmian Cleveland Cable Catalogue — UK SWA cable data

• cable derating and grouping factors — Cable selection before glanding

• safe isolation procedure — Working on existing SWA safely

• earthing and bonding — How SWA fits in the wider earth system

• part p electrical safety — Notification and certification