Application & Operating Conditions
BS 6708 Type 7 is a 640/1100 V heavy-duty flexible trailing cable (16 to 150 mm²) designed to supply mobile coalcutters, longwall shearers, roadheaders, and crushing machines in deep underground mines and surface workings where explosive methane (firedamp) and coal dust can accumulate.
Longwall Coalcutters & Face Shearers
Withstands continuous dragging, flexing, and cable-handler guidance along underground armoured face conveyors (AFC) with pulling tension ratings up to 2,000 kgf.
Firedamp & Coal Dust Fault Interception
Individual composite tinned-copper and nylon braided phase screens stay in continuous intimate contact with the central bare earth conductor to trip gate-end earth-leakage relays instantly.
Excavating & Mobile Crushing Plant
Heavy-duty polychloroprene (PCP) rubber outer sheath resists rock abrasion, mineral cutting oils, acid mine water, and flame propagation in arduous quarry and tunnel headings.
Pilot Screening Engineering Note (BS 6708): Type 7 incorporates an unscreened single pilot core for intrinsically safe gate-end interlock circuits. Where an individually screened pilot core is mandated, specify BS 6708 Type 7M; for 3-channel pilot control, specify BS 6708 Type 7S.
Cable Construction (BS 6708 Type 7)
Manufactured to British Standard BS 6708, Type 7 combines Class 5 flexible tinned copper conductors, thermoset EPR dielectric, and resilient copper/nylon composite screens laid around a central uninsulated earth core.
| Layer / Component | Material & BS 6708 Engineering Specification |
|---|---|
| 1. Conductors | Electrolytic stranded tinned annealed copper wire, IEC 60228 Class 5 (phase, pilot, and central earth) |
| 2. Core Insulation | High-grade thermosetting EPR (Ethylene Propylene Rubber) on phase and pilot cores; central ground core is uninsulated |
| 3. Core Identification | Coloured textile separator tape over EPR insulation (Red, Yellow, Brown phases; Blue pilot) |
| 4. Phase Screen | Tinned copper wire and nylon yarn composite braided screen over each of the three phase cores (pilot core unscreened) |
| 5. Core Lay-Up | Three screened phase cores and one unscreened pilot core laid up in direct electrical contact around the central bare earth conductor |
| 6. Inner Bedding | Extruded elastomeric rubber-based bedding compound filling core interstices |
| 7. Outer Sheath | Heavy-duty flame-retardant, oil- and abrasion-resistant chloroprene (PCP) outer sheath (black) |
BS 6708 Type 7 Cross-Section: Three composite-screened EPR phase cores and one unscreened blue pilot core laid symmetrically in contact with the central bare tinned copper earth conductor.
Technical Characteristics
Verified to BS 6708 electrical and mechanical test schedules, Type 7 supports 3 kV AC dielectric proof testing, low earth-fault loop impedance, and tight dynamic bending radii from 309 mm to 627 mm.
| Parameter | BS 6708 Rated Value |
|---|---|
| Manufacturing Standard | BS 6708 (Flexible cables for use at mines and quarries) |
| Rated Voltage (U0/U) | 640/1100 V AC |
| AC Routine Test Voltage | 3 kV |
| Conductor Flexibility | IEC 60228 Class 5 flexible stranded tinned copper |
| Continuous / Intermittent Current (@ 25 °C) | 85 A to 320 A continuous | 96 A to 385 A intermittent |
| Minimum Bending Radius | 309 mm (3×16 mm²) to 627 mm (3×150 mm²) — approx. 8× Max OD |
| Maximum Pulling Tension | 480 kgf (3×16 mm²) up to 2,000 kgf (95–150 mm²) |
| Flame, Oil & Abrasion Resistance | Heavy-duty PCP elastomeric compound for underground fiery mines |
Specification, Dimensional & Electrical Data (8 Standard Sizes)
Complete BS 6708 Type 7 dimensional and electrical tables covering 16 mm² to 150 mm² coalcutter power cross-sections, pulling tensions, ampacities, and earth-screen resistance.
BS 6708 Type 7 — Core Construction & Cable Mechanical Dimensions (8 Sizes)
| Nominal Size (mm²) | Phase Stranding (No./mm) | Cond. Dia. (mm) | Insul. Dia. (mm) | Screen Dia. (mm) | Earth / Pilot (mm²) | Min–Max OD (mm) | Min. Bend (mm) | Max Pull (kgf) | Cable Wt. (kg/km) | Copper Wt. (kg/km) |
|---|---|---|---|---|---|---|---|---|---|---|
| 3×16+16+16 | 126/0.40 | 5.50 | 8.85 | 11.15 | 1×16 / 1×16 | 35.8 – 38.6 | 309 | 480 | 2400 | 1070 |
| 3×25+16+16 | 196/0.40 | 6.75 | 10.35 | 12.65 | 1×16 / 1×16 | 39.7 – 42.9 | 343 | 642 | 2950 | 1330 |
| 3×35+18+16 | 276/0.40 | 8.00 | 11.60 | 13.90 | 1×18 / 1×16 | 43.1 – 46.3 | 370 | 834 | 3520 | 1690 |
| 3×50+25+25 | 396/0.40 | 9.75 | 13.60 | 15.90 | 1×25 / 1×25 | 48.5 – 51.8 | 414 | 1200 | 4600 | 2320 |
| 3×70+35+35 | 360/0.50 | 11.60 | 15.70 | 18.00 | 1×35 / 1×35 | 55.1 – 58.8 | 470 | 1680 | 6200 | 3190 |
| 3×95+50+50 | 475/0.50 | 12.75 | 17.25 | 19.55 | 1×50 / 1×50 | 62.4 – 66.1 | 529 | 2000 | 7900 | 4300 |
| 3×120+50+70 | 608/0.50 | 15.10 | 20.05 | 22.35 | 1×50 / 1×70 | 68.0 – 72.5 | 580 | 2000 | 9650 | 5100 |
| 3×150+70+95 | 740/0.50 | 17.00 | 22.20 | 24.50 | 1×70 / 1×95 | 70.4 – 78.4 | 627 | 2000 | 11500 | 6500 |
BS 6708 Type 7 — Current Ratings & Electrical Impedance Details (8 Sizes)
| Nominal Size (mm²) | Cont. Current @ 25°C (A) | Interm. Current @ 25°C (A) | Phase DC Res. 20°C (Ω/km) | Pilot DC Res. 20°C (Ω/km) | Screens+Earth Res. (Ω/km) | Reactance 50Hz (Ω/km) | Reactance 60Hz (Ω/km) | Min. Insul. Res. (MΩ·km) | Volt Drop (mV/A/m) |
|---|---|---|---|---|---|---|---|---|---|
| 3×16+16+16 | 85 | 96 | 1.24 | 1.24 | 0.66 | 0.109 | 0.131 | 435 | 2.62 |
| 3×25+16+16 | 110 | 125 | 0.795 | 1.24 | 0.56 | 0.107 | 0.128 | 375 | 1.68 |
| 3×35+18+16 | 135 | 150 | 0.565 | 1.24 | 0.54 | 0.101 | 0.121 | 325 | 1.20 |
| 3×50+25+25 | 170 | 200 | 0.393 | 0.795 | 0.44 | 0.098 | 0.118 | 285 | 0.84 |
| 3×70+35+35 | 205 | 250 | 0.277 | 0.565 | 0.30 | 0.095 | 0.114 | 260 | 0.61 |
| 3×95+50+50 | 250 | 310 | 0.210 | 0.393 | 0.26 | 0.094 | 0.113 | 250 | 0.47 |
| 3×120+50+70 | 295 | 355 | 0.164 | 0.277 | 0.24 | 0.092 | 0.110 | 250 | 0.38 |
| 3×150+70+95 | 320 | 385 | 0.132 | 0.210 | 0.176 | 0.080 | 0.096 | 250 | 0.32 |
Selection Guide: BS 6708 640/1100V Trailing Cable Family
Compare BS 6708 640/1100 V trailing cable designations across pilot screening, multi-pilot control units, and cradle vs. central-earth geometries.
| BS 6708 Model | Core & Pilot Architecture, Earth Design & Primary Duty |
|---|---|
| BS 6708 Type 7 (This Product) | 3 composite-screened phase cores + 1 unscreened single pilot core + central bare tinned-copper earth (16–150 mm², 8 sizes) for standard 640/1100 V coalcutters and face shearers. |
| BS 6708 Type 7M | BS 6708 Type 7M: 3 composite-screened phase cores + 1 individually screened pilot core (equal phase/pilot size up to 150 mm²) + central bare earth for enhanced pilot earth-fault segregation. |
| BS 6708 Type 7S | BS 6708 Type 7S: 3 composite-screened phase cores + 1 unscreened 3-core pilot sub-unit (3×4 to 3×10 mm²) + central bare earth (50–150 mm²) for multi-channel interlock/telemetry control. |
| BS 6708 Type 11 | BS 6708 Type 11: 3 composite-screened phase cores + 1 composite-screened pilot core (3×16+16 mm²) laid up around an elastomeric rubber cradle (earth continuity via contacting screens). |
| BS 6708 Type 14 | BS 6708 Type 14: 5-core cradle layout: 3 composite-screened phase cores + 1 unscreened pilot core + 1 unscreened insulated earth core (25–95 mm²) around an elastomeric centre. |
| BS 6708 Type 16 | BS 6708 Type 16: Compact trefoil layout: 3 composite-screened phase cores + 2 unscreened interstitial earth cores + 1 unscreened pilot core tucked into outer valleys (25–95 mm²) for reduced overall diameter. |
Frequently Asked Questions (FAQ)
Engineering answers on BS 6708 Type 7 composite braid screens, central bare earth design, and Restrained plug termination.
Why does BS 6708 Type 7 use a composite tinned-copper and nylon braided screen?
Combining tinned copper wires with high-tenacity nylon yarns in a single composite braid preserves high earth-fault conductivity (0.176–0.66 Ω/km combined with the central earth) while allowing repeated flexing and torsional recovery without metallic wire breakage.
What is the difference between BS 6708 Type 7 and Type 7M?
Type 7 features three individually screened phase cores and one unscreened pilot core, whereas Type 7M equips both the three phase cores and the pilot core (4 screened cores total) with composite copper/nylon screens and full-sized pilot cross-sections.
Can TEBAOFLEX supply BS 6708 Type 7 cables cut to custom face lengths?
Yes. We manufacture BS 6708 Type 7 trailing cables in continuous longwall face or gate-road drum lengths, fully compatible with standard British 650/1100 V restrained flameproof plugs and sockets (BS 5620).
Request a Quote for BS 6708 Type 7 Coalcutter Trailing Cables
Send your required cross-section (3×16 to 3×150 mm²), face length, and delivery port for factory-direct pricing and full routine test certificates.
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