Application & Operating Conditions
BS 6708 Type 20 (3-core) and Type 21 (4-core) are 640/1100 V pliable wire armoured (PWA) flexible power supply cables engineered for underground excavating and crushing machinery, roadway gate-end distribution, haulage winches, and surface mineral processing plant where explosive gases and combustible coal dust can accumulate.
Semi-Mobile Excavating & Crushing Plant
Combines Class 5 flexible tinned copper conductors with multi-wire stranded steel armour so heavy gate-end feeders can be coiled, dragged forward, and re-routed as underground crushing stations advance.
Graduated Pliable Steel Armour (7/0.45–7/1.25)
Armour strand gauge scales systematically with cross-section—from 7/0.45 mm (2.5–4 mm²) and 7/0.71 mm (6–16 mm²) up to 7/0.90 mm (25–120 mm²) and 7/1.25 mm (150 mm²)—maintaining low earth-fault impedance.
Non-Contacting Cradle Core Geometry
All three (Type 20) or four (Type 21) EPR cores sit in dedicated recesses around a central elastomeric cradle without touching each other, preventing internal core pinching under heavy rockfall impact.
Type 20 vs Type 21 Selection Rule: Specify Type 20 (3-core, 3×2.5 to 3×150 mm²) for 3-phase power feeds utilizing the high-conductance galvanized pliable wire armour as the earth path, or Type 21 (4-core, 4×2.5 to 4×150 mm²) when a fourth insulated internal earth or pilot core is required alongside the steel armour.
Cable Construction (BS 6708 Type 20 & Type 21 Pliable Armour)
Manufactured strictly to British Standard BS 6708 with non-contacting EPR power cores around an elastomeric centre, cushioned in thick rubber bedding beneath stranded galvanized steel pliable wire armour.
| Layer / Component | Material & BS 6708 Engineering Specification |
|---|---|
| 1. Conductors | Electrolytic flexible stranded tinned copper wire, IEC 60228 Class 5 (2.5 mm² to 150 mm², 50/0.25 mm up to 740/0.50 mm stranding). |
| 2. Core Insulation | Extruded Ethylene Propylene Rubber (EPR) dielectric, 1.4 mm to 2.3 mm radial thickness graded by conductor cross-section. |
| 3. Cradle & Core Lay-Up | Three unscreened cores (Type 20) or four unscreened cores (Type 21) laid up around a profiled elastomeric cradle without contacting each other. |
| 4. Inner Sheath / Bedding | Extruded rubber-based inner bedding compound, 2.0 mm to 5.0 mm radial thickness. |
| 5. Pliable Wire Armour (PWA) | Helical layer of 7-wire galvanized steel pliable armour strands (7/0.45 mm, 7/0.71 mm, 7/0.90 mm, or 7/1.25 mm) between inner and outer sheaths. |
| 6. Outer Sheath | Heavy-duty black polychloroprene (PCP / chloroprene) outer sheath (2.5 mm to 7.3 mm radial thickness), resistant to abrasion, oils, mine water, and flame propagation. |
BS 6708 Type 20 / Type 21 Cross-Section (Type 21 Shown): Unscreened EPR-insulated Class 5 tinned copper cores positioned around a central elastomeric cradle, enclosed by rubber inner bedding, galvanized steel pliable wire armour, and a black PCP outer sheath.
Technical Characteristics
Complete electrical, routine test, and dimensional ratings verified in accordance with British Standard BS 6708 Type 20 and Type 21.
| Parameter | BS 6708 Rated Value |
|---|---|
| Reference Standard | BS 6708 (Type 20 & Type 21 Pliable Wire Armoured Mining Power Cables) |
| Rated Voltage (Uo/U) | 640 / 1100 V AC |
| Routine AC Test Voltage | 3 kV AC |
| Size Range | Type 20: 3×2.5 to 3×150 mm² (12 Sizes) | Type 21: 4×2.5 to 4×150 mm² (12 Sizes) |
| Pliable Armour Gauges | 7/0.45 mm (2.5–4 mm²), 7/0.71 mm (6–16 mm²), 7/0.90 mm (25–120 mm²), 7/1.25 mm (150 mm²) |
| Minimum Bending Radius | Type 20: 243–786 mm | Type 21: 258–858 mm (approx. 9 × Max. OD) |
| Continuous Current Rating (@ 25 °C) | 28 A (2.5 mm²) up to 320 A (150 mm²) |
| Armour Max. DC Resistance (@ 20 °C) | Type 20: 4.6 to 0.45 Ω/km | Type 21: 4.2 to 0.41 Ω/km |
BS 6708 Type 20 & Type 21 Complete Specification Tables (24 Sizes)
Full conductor stranding, sheath thicknesses, pliable armour gauges, maximum outer diameters, bend radii, weights, current ratings, and DC resistances for all 12 Type 20 sizes and 12 Type 21 sizes.
1. BS 6708 Type 20 — 3-Core Unscreened Pliable Wire Armoured Cable (3×2.5 to 3×150 mm²)
| Nominal Size (mm²) | Stranding (No./mm) | Cond. Dia. (mm) | Insul. Thick. (mm) | Inner Sheath (mm) | Armour Size (No./mm) | Outer Sheath (mm) | Max. OD (mm) | Min. Bend Radius (mm) | Approx. Weight (kg/km) | Copper Weight (kg/km) | Current @ 25 °C (A) | Cond. DC Res. (Ω/km) | Armour DC Res. (Ω/km) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 3×2.5 | 50/0.25 | 2.10 | 1.4 | 2.0 | 7/0.45 | 2.5 | 26.9 | 243 | 990 | 72 | 28 | 8.21 | 4.6 |
| 3×4 | 56/0.30 | 2.70 | 1.4 | 2.0 | 7/0.45 | 2.5 | 28.2 | 254 | 1150 | 115 | 37 | 5.09 | 4.2 |
| 3×6 | 84/0.30 | 3.30 | 1.5 | 2.5 | 7/0.71 | 3.8 | 36.5 | 329 | 2000 | 173 | 46 | 3.39 | 2.2 |
| 3×10 | 80/0.40 | 4.40 | 1.5 | 2.5 | 7/0.71 | 3.8 | 38.4 | 346 | 2350 | 288 | 63 | 1.95 | 2.0 |
| 3×16 | 126/0.40 | 5.50 | 1.5 | 2.5 | 7/0.71 | 3.8 | 40.8 | 368 | 2750 | 461 | 85 | 1.24 | 1.9 |
| 3×25 | 196/0.40 | 7.10 | 1.6 | 2.5 | 7/0.90 | 4.0 | 47.0 | 423 | 3350 | 720 | 110 | 0.795 | 1.3 |
| 3×35 | 276/0.40 | 8.40 | 1.6 | 2.5 | 7/0.90 | 4.3 | 50.6 | 456 | 4300 | 1008 | 135 | 0.565 | 1.2 |
| 3×50 | 396/0.40 | 10.10 | 1.7 | 2.5 | 7/0.90 | 4.7 | 56.7 | 511 | 5320 | 1440 | 170 | 0.393 | 1.1 |
| 3×70 | 360/0.50 | 11.90 | 1.8 | 2.5 | 7/0.90 | 5.2 | 62.7 | 565 | 6750 | 2016 | 205 | 0.277 | 0.94 |
| 3×95 | 475/0.50 | 13.90 | 2.0 | 3.8 | 7/0.90 | 5.8 | 72.1 | 649 | 8750 | 2736 | 250 | 0.210 | 0.80 |
| 3×120 | 629/0.50 | 15.80 | 2.2 | 3.8 | 7/0.90 | 6.2 | 77.0 | 693 | 10650 | 3456 | 295 | 0.164 | 0.74 |
| 3×150 | 740/0.50 | 17.00 | 2.3 | 5.0 | 7/1.25 | 6.6 | 87.3 | 786 | 12500 | 4320 | 320 | 0.132 | 0.45 |
2. BS 6708 Type 21 — 4-Core Unscreened Pliable Wire Armoured Cable (4×2.5 to 4×150 mm²)
| Nominal Size (mm²) | Stranding (No./mm) | Cond. Dia. (mm) | Insul. Thick. (mm) | Inner Sheath (mm) | Armour Size (No./mm) | Outer Sheath (mm) | Max. OD (mm) | Min. Bend Radius (mm) | Approx. Weight (kg/km) | Copper Weight (kg/km) | Current @ 25 °C (A) | Cond. DC Res. (Ω/km) | Armour DC Res. (Ω/km) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 4×2.5 | 50/0.25 | 2.10 | 1.4 | 2.0 | 7/0.45 | 2.5 | 28.6 | 258 | 1150 | 96 | 28 | 8.21 | 4.2 |
| 4×4 | 56/0.30 | 2.70 | 1.4 | 2.0 | 7/0.45 | 2.5 | 30.1 | 271 | 1320 | 154 | 37 | 5.09 | 3.9 |
| 4×6 | 84/0.30 | 3.30 | 1.5 | 2.5 | 7/0.71 | 3.8 | 38.8 | 350 | 2350 | 230 | 46 | 3.39 | 2.0 |
| 4×10 | 80/0.40 | 4.40 | 1.5 | 2.5 | 7/0.71 | 3.8 | 41.0 | 369 | 2740 | 384 | 63 | 1.95 | 1.9 |
| 4×16 | 126/0.40 | 5.50 | 1.5 | 2.5 | 7/0.71 | 3.9 | 44.0 | 396 | 3170 | 614 | 85 | 1.24 | 1.7 |
| 4×25 | 196/0.40 | 7.10 | 1.6 | 2.5 | 7/0.90 | 4.3 | 49.8 | 449 | 4030 | 960 | 110 | 0.795 | 1.5 |
| 4×35 | 276/0.40 | 8.40 | 1.6 | 2.5 | 7/0.90 | 4.7 | 56.1 | 505 | 5220 | 1344 | 135 | 0.565 | 1.1 |
| 4×50 | 396/0.40 | 10.10 | 1.7 | 2.5 | 7/0.90 | 5.1 | 61.8 | 557 | 6400 | 1920 | 170 | 0.393 | 0.96 |
| 4×70 | 360/0.50 | 11.90 | 1.8 | 2.5 | 7/0.90 | 5.7 | 71.4 | 643 | 8060 | 2688 | 205 | 0.277 | 0.80 |
| 4×95 | 475/0.50 | 13.90 | 2.0 | 3.8 | 7/0.90 | 6.3 | 78.6 | 708 | 10650 | 3648 | 250 | 0.210 | 0.73 |
| 4×120 | 629/0.50 | 15.80 | 2.2 | 3.8 | 7/0.90 | 6.8 | 89.0 | 801 | 13450 | 4608 | 295 | 0.164 | 0.47 |
| 4×150 | 740/0.50 | 17.00 | 2.3 | 5.0 | 7/1.25 | 7.3 | 95.3 | 858 | 15300 | 5760 | 320 | 0.132 | 0.41 |
Selection Guide: BS 6708 Pliable Wire Armoured (PWA) Mining Cables
Compare BS 6708 Type 20/21 against screened 640/1100 V (Type 62–64, Type 201/211) and medium-voltage (Type 321/331, Type 621) pliable wire armoured feeders.
| BS 6708 Model | Core & Pilot Architecture, Earth Design & Primary Duty |
|---|---|
| BS 6708 Type 20 & Type 21 (640/1100V Unscreened PWA) (This Product) | 3-core (Type 20) and 4-core (Type 21) unscreened EPR power cables (2.5–150 mm², 24 sizes) with 7/0.45–7/1.25 mm galvanized steel pliable wire armour. |
| BS 6708 Type 62, 63 & 64 (640/1100V Screened 4 mm² PWA) | BS 6708 Type 62, 63 & 64 (640/1100V Screened 4 mm² PWA): 2×4, 3×4, and 4×4 mm² individually composite-screened pliable wire armoured cables for 640/1100 V coalface lighting and auxiliary equipment. |
| BS 6708 Type 201 & Type 211 (640/1100V Yellow-Stripe Roadway) | BS 6708 Type 201 & Type 211 (640/1100V Yellow-Stripe Roadway): BS 6708:1998 3-core (Type 201) and 3+Earth (Type 211) copper/nylon screened MEPR roadway & quarry trailing cables (10–120 mm²) with yellow-striped black PCP jacket. |
| BS 6708 Type 321 & Type 331 (1.9/3.3kV Blue-Stripe Roadway) | BS 6708 Type 321 & Type 331 (1.9/3.3kV Blue-Stripe Roadway): BS 6708:1998 1900/3300 V medium-voltage pliable wire armoured roadway & quarry trailing cables (25–150 mm²; screened Type 331 / unscreened Type 321) with blue-striped black PCP sheath. |
| BS 6708 Type 621 (3.8/6.6kV Heavy MV Armoured) | BS 6708 Type 621 (3.8/6.6kV Heavy MV Armoured): 3800/6600 V medium-voltage 4-core (3 phases + 1 pilot, 4×35–4×150 mm²) unscreened 5.0 mm EPR pliable wire armoured power cable tested at 15 kV AC. |
| BS 6708 Type 70 & Type 71 (320/550V Lighting PWA) | BS 6708 Type 70 & Type 71 (320/550V Lighting PWA): 4×4 and 5×4 mm² 320/550 V unscreened pliable wire armoured cables for low-voltage coalface lighting strings. |
Frequently Asked Questions (FAQ)
Engineering FAQs regarding BS 6708 Type 20/21 vs Type 201/211, pliable armour termination, and earth-fault loop impedance.
When should I specify BS 6708 Type 20/21 instead of Type 201/211?
Specify BS 6708 Type 20 or Type 21 when your 640/1100 V feeder requires unscreened EPR cores—including smaller auxiliary cross-sections (2.5, 4, and 6 mm²) or large 150 mm² crushing plant feeds—relying on the galvanized steel pliable wire armour (and fourth core in Type 21) for earth protection. Specify Type 201 or Type 211 (10–120 mm²) when individual composite copper/nylon phase screens and a yellow-striped roadway extension jacket are required.
Can BS 6708 Type 20/21 be terminated into standard flameproof mining glands and bolted couplers?
Yes. The stranded 7-wire galvanized steel pliable armour (7/0.45 mm to 7/1.25 mm) clamps securely into standard BS 6708 / Ex d mining armour cone glands while providing far greater bending resilience at gland entries than single-wire SWA cables.
Are all conductors tinned copper across the full 2.5–150 mm² range?
Yes. Every conductor in TEBAOFLEX BS 6708 Type 20 and Type 21 uses electrolytic annealed flexible stranded tinned copper wire (IEC 60228 Class 5) to prevent sulfur vulcanization corrosion from rubber compounds and resist damp corrosive mine atmospheres.
Request Factory Pricing for BS 6708 Type 20 or Type 21 Cable
Send your required Type (3-core Type 20 or 4-core Type 21), conductor cross-section (2.5–150 mm²), and drum lengths for a 12-hour engineering quotation.
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