Application & Operating Conditions
BS 6708 Type 70 and Type 71 are 320/550 V pliable wire armoured (PWA) flexible cables used for coalface roadway lighting strings, auxiliary crushing and excavating plant, and semi-mobile stage-loader substations in deep mines where explosive gases and coal dust accumulate, as well as heavy-duty surface quarries.
Coalface & Roadway Lighting Systems
Widely specified as the backbone interconnecting feeder between flameproof lighting transformers and armoured roadway luminaire fittings along advancing or retreating longwall gates.
Pliable Steel Strand Armour (7/0.45 mm)
Unlike rigid single-wire SWA cables, BS 6708 pliable armour uses stranded 7×0.45 mm galvanized steel wire bundles—combining rockfall crush protection with 234–247 mm bending flexibility.
High-Conductance Earth Armour Path
The helical galvanized steel pliable armour maintains a low maximum DC resistance of 5.07 Ω/km (Type 70) and 4.63 Ω/km (Type 71), matching the 5.09 Ω/km phase conductor resistance.
Type 70 vs Type 71 Quick Choice: Specify Type 70 (4×4 mm²) for 3-phase + earth or 3-phase lighting circuits using the pliable armour plus fourth core, and Type 71 (5×4 mm²) when an additional pilot-interlock, switched lighting phase, or dedicated neutral conductor is required.
Cable Construction (BS 6708 Type 70 & Type 71 Pliable Armour)
Built to BS 6708 with four (Type 70) or five (Type 71) unscreened 4 mm² EPR cores enclosed inside a dual-sheath rubber/PCP envelope reinforced by 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 (56/0.30 mm stranding, 2.60 mm diameter, 4 mm² nominal cross-section). |
| 2. Core Insulation | Extruded Ethylene Propylene Rubber (EPR) insulation, 1.0 mm nominal radial thickness. |
| 3. Core Lay-Up | Four unscreened cores (Type 70) or five unscreened cores (Type 71) laid up in contact with each other in a compact circular assembly. |
| 4. Inner Sheath / Bedding | Extruded rubber-based inner bedding compound, 2.0 mm radial thickness (15.8–17.8 mm diameter on Type 70; 17.2–19.2 mm on Type 71). |
| 5. Pliable Wire Armour (PWA) | Helical layer of galvanized steel pliable wire strands (7/0.45 mm strand construction) applied between the inner and outer sheaths. |
| 6. Outer Sheath | Heavy-duty black chloroprene (PCP) outer sheath, 2.5 mm nominal radial thickness, resistant to mine water, oils, rock impact, and flame spread. |
BS 6708 Type 70 / 71 Cross-Section: Unscreened Class 5 tinned copper EPR cores cushioned in 2.0 mm rubber inner bedding, armoured with 7/0.45 mm galvanized steel pliable wire strands, and oversheathed in 2.5 mm black PCP.
Technical Characteristics
Dimensional, mechanical, and electrical characteristics compliant with British Standard BS 6708 Type 70 and Type 71.
| Parameter | BS 6708 Rated Value |
|---|---|
| Reference Standard | BS 6708 (Pliable Wire Armoured Mining Power & Coalface Lighting Cables) |
| Rated Voltage (Uo/U) | 320 / 550 V AC |
| Routine AC Test Voltage | 1.5 kV AC |
| Model Breakdown | Type 70: 4×4 mm² Unscreened + PWA | Type 71: 5×4 mm² Unscreened + PWA |
| Armour Wire Construction | 7/0.45 mm Galvanized Steel Pliable Wire Strands |
| Minimum Bending Radius | 234 mm (Type 70) / 247 mm (Type 71) |
| Max. Pulling Tension | 96 kgf (Type 70) / 100 kgf (Type 71) |
| Continuous Current & DC Resistance | 28 A (@ 25 °C) | Phase Cond.: 5.09 Ω/km | Armour: 5.07 Ω/km (T70) / 4.63 Ω/km (T71) |
BS 6708 Type 70 & Type 71 Complete Specification Tables
Full dimensional, armour, mechanical, current, and resistance specifications for BS 6708 Type 70 (4×4 mm²) and Type 71 (5×4 mm²).
1. Core, Inner Sheath, Pliable Armour & Overall Dimensions
| BS 6708 Type | Nominal Size (mm²) | Stranding (No./mm) | Cond. Dia. (mm) | Insul. Thick. (mm) | Inner Sheath (mm) | Inner Sheath Dia. (mm) | Armour Size (No./mm) | Outer Sheath (mm) | Min. OD (mm) | Max. OD (mm) |
|---|---|---|---|---|---|---|---|---|---|---|
| Type 70 | 4×4 | 56/0.30 | 2.60 | 1.0 | 2.0 | 15.8 – 17.8 | 7/0.45 | 2.5 | 23.5 | 26.0 |
| Type 71 | 5×4 | 56/0.30 | 2.60 | 1.0 | 2.0 | 17.2 – 19.2 | 7/0.45 | 2.5 | 24.9 | 27.4 |
2. Mechanical Ratings, Current Capacity & DC Resistance
| BS 6708 Type | Nominal Size (mm²) | Min. Bend Radius (mm) | Max. Pulling Tension (kgf) | Approx. Weight (kg/km) | Copper Weight (kg/km) | Current @ 25 °C (A) | Phase Cond. DC Res. (Ω/km) | Armour DC Res. (Ω/km) |
|---|---|---|---|---|---|---|---|---|
| Type 70 | 4×4 | 234 | 96 | 1100 | 154 | 28 | 5.09 | 5.07 |
| Type 71 | 5×4 | 247 | 100 | 1230 | 192 | 28 | 5.09 | 4.63 |
Selection Guide: BS 6708 Auxiliary, Lighting & Control Cables
Compare BS 6708 Type 70 & Type 71 against multi-core armoured control cables (Types 506–524) and other BS 6708 underground cables.
| BS 6708 Model | Core & Pilot Architecture, Earth Design & Primary Duty |
|---|---|
| BS 6708 Type FS4 (640/1100V Flat) | BS 6708 Type FS4 (640/1100V Flat): Flat parallel 4-core geometry (4×2.5 & 4×4 mm²) with tinned copper braided screens on all phase and pilot cores for monorail festoon and overhead catenary loops (100–120 mm bend radius). |
| BS 6708 Type 44 (125/72V Screened Drill) | BS 6708 Type 44 (125/72V Screened Drill): 5×6 mm² handheld drilling machine cable with composite copper/nylon braided screens on 3 phase cores + unscreened pilot & earth cores around an elastomeric cradle. |
| BS 6708 Type 43 (125/72V Conducting Rubber Drill) | BS 6708 Type 43 (125/72V Conducting Rubber Drill): 5×6 mm² metal-braid-free drilling cable with cores separated around a semiconducting elastomeric cradle and 1.5 mm conducting rubber inner sheath for non-fraying flex fatigue resistance. |
| BS 6708 Type 70 & Type 71 (320/550V Armoured) (This Product) | 4-core (Type 70, 4×4 mm²) and 5-core (Type 71, 5×4 mm²) unscreened EPR power & coalface lighting cables protected by 7/0.45 mm galvanized steel pliable wire armour. |
| BS 6708 Type 506 / 512 / 518 / 524 (320/550V Control) | BS 6708 Type 506 / 512 / 518 / 524 (320/550V Control): 6-, 12-, 18-core (1.34 mm²) and 24-core (0.93 mm²) individually composite-screened & pliable wire armoured control cables for inter-segment mining machine telemetry and pilot interlocks. |
| BS 6708 Type 7 (640/1100V Trailing) | BS 6708 Type 7 (640/1100V Trailing): Primary 640/1100 V unarmoured coalcutter trailing feeder (16–150 mm²) with 3 composite-screened phase cores, 1 unscreened pilot core, and central bare earth. |
Frequently Asked Questions (FAQ)
Answers to common engineering questions on BS 6708 pliable wire armour (PWA) vs standard SWA and voltage upgrades.
How does BS 6708 pliable wire armour (7/0.45 mm) differ from standard BS 5467 SWA?
Standard BS 5467 SWA cables use solid single galvanized steel wires over rigid XLPE/PVC bedding for fixed installation only. BS 6708 Type 70 and Type 71 use 7-wire stranded 0.45 mm galvanized steel bundles over flexible EPR/rubber bedding, allowing repeated relocation as coalface lighting and crushing equipment advance with the face.
What if our circuit requires 640/1100 V or individually screened 4 mm² armoured cores?
BS 6708 Type 70 and Type 71 are unscreened cables rated at 320/550 V. For 640/1100 V pliable wire armoured circuits, specify BS 6708 Type 20/21 (unscreened, 2.5–150 mm²) or BS 6708 Type 62/63/64 (individually composite-screened 4 mm² pliable wire armoured cables).
Does the galvanized pliable armour meet earth-fault conductance requirements?
Yes. The 7/0.45 mm galvanized steel pliable armour provides a maximum DC resistance at 20 °C of 5.07 Ω/km on Type 70 and 4.63 Ω/km on Type 71—equal to or lower than the 5.09 Ω/km resistance of the 4 mm² tinned copper phase conductors.
Request a Quote for BS 6708 Type 70 or Type 71 Cable
Specify Type 70 (4×4 mm²) or Type 71 (5×4 mm²), required drum lengths, and destination port for a rapid factory quotation.
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