Application & Operating Conditions
BS 6708:1998 Type 321 and Type 331 are 1900/3300 V medium-voltage pliable wire armoured (PWA) roadway extension and quarry trailing cables designed to deliver 3.3 kV three-phase power to longwall gate-end transformers, mobile quarry primary crushers, electric face shovels, and deep-mine pumping stations.
3.3 kV Longwall Gate & Quarry Feeders
Supports long-distance 3.3 kV distribution up to 320 A (150 mm²) with voltage drop as low as 0.32 mV/A/m and high-tensile pliable steel wire armour rated up to 2000 kgf pull.
Type 331 (Screened) vs Type 321 (Unscreened)
Type 331 encloses all three 3.3 kV MEPR phase cores in composite copper/nylon braided screens (0.550–1.350 Ω/km parallel); Type 321 omits core screens for unscreened 3.3 kV quarry installations.
Blue-Striped 3.3 kV PCP Outer Jacket
Extruded longitudinal blue identification stripe on the black flame-retardant PCP sheath gives immediate underground visual verification of live 1900/3300 V medium-voltage circuits.
3.3 kV Selection Guidance: For underground coal mines and quarries operating earth-fault-restricted 3.3 kV switchgear, BS 6708 Type 331 (with composite copper/nylon phase screens + Green/Yellow earth core + pliable steel wire armour) provides maximum phase-to-earth fault containment.
Cable Construction (BS 6708:1998 Type 331 & Type 321)
Constructed to BS 6708:1998 with heavy-wall MEPR 3.3 kV insulation, symmetrical 4-core cradle geometry, extruded PCP inner bedding, pliable galvanized steel wire armour, and a blue-striped black PCP outer jacket.
| Layer / Component | Material & BS 6708 Engineering Specification |
|---|---|
| 1. Conductors | Flexible stranded tinned annealed copper conductors for three power phases (25–150 mm²) plus one dedicated earth conductor (16–120 mm²). |
| 2. Medium-Voltage Insulation | Heavy-wall Minerally reinforced Ethylene Propylene Rubber (MEPR) rated for 1900/3300 V (6.5 kV AC routine test), with Red, Yellow, and Brown phase identification and Green/Yellow earth identification. |
| 3. Phase Screens (Type 331 Only) | Type 331 applies a composite copper/nylon braided screen over each of the three phase cores; Type 321 uses unscreened power cores. |
| 4. Elastomeric Cradle Lay-Up | Three power cores and one unscreened Green/Yellow earth core laid up symmetrically around a central elastomeric cradle. |
| 5. Inner Bedding Sheath | Extruded polychloroprene (PCP) inner bedding compound (42.2–74.0 mm diameter). |
| 6. Pliable Wire Armour (PWA) | Helical layer of pliable galvanized steel wire armour strands (0.240–0.990 Ω/km max DC resistance at 20 °C). |
| 7. Overall Sheath | Heavy-duty flame-retardant black polychloroprene (PCP) compound with longitudinal blue stripe. |
BS 6708 Type 321 / 331 Cross-Section (Type 331 Shown): Three composite-screened 3.3 kV MEPR phase cores plus one Green/Yellow earth core around an elastomeric centre, protected by PCP inner bedding, pliable galvanized steel wire armour, and a blue-striped black PCP sheath.
Technical Characteristics
Complete electrical, dielectric, reactance, and mechanical parameters per BS 6708:1998 Type 331 and Type 321.
| Parameter | BS 6708 Rated Value |
|---|---|
| Reference Standard | BS 6708:1998 (Type 321 & Type 331 1900/3300 V Pliable Wire Armoured Cables) |
| Rated Voltage (Uo/U) | 1900 / 3300 V AC (1.9 / 3.3 kV) |
| Routine AC Test Voltage | 6.5 kV AC |
| Jacket Identification | Black Heavy-Duty Flame-Retardant PCP with Longitudinal Blue Stripe |
| Minimum Insulation Resistance | 600 to 1250 MΩ·km across power cores |
| Minimum Bending Radius | Type 331: 620–980 mm | Type 321: 640–940 mm |
| Maximum Pulling Tension | 540 to 2000 kgf |
| Continuous Current Rating (@ 25 °C) | 110 A (25 mm²) up to 320 A (150 mm²) |
BS 6708 Type 331 & Type 321 Complete Specification Tables (12 MV Sizes)
Full dimensional, pulling tension, weight, ampacity, DC resistance, 50/60 Hz reactance, insulation resistance, and voltage-drop tables.
1. BS 6708 Type 331 (3.3 kV Screened Phases + Earth) — Dimensions, Pull & Weight (25–150 mm²)
| Phase + Earth (mm²) | Phase Insul. Dia. (mm) | Phase Screen Dia. (mm) | Earth CSA (mm²) | Earth Insul. Dia. (mm) | Inner Sheath Min–Max (mm) | Overall OD Min (mm) | Overall OD Max (mm) | Min. Bend Radius (mm) | Max. Pull (kgf) | Approx. Weight (kg/km) |
|---|---|---|---|---|---|---|---|---|---|---|
| 3×25 + 16E | 13.50 | 15.50 | 16 | 15.50 | 42.20 – 44.70 | 57.80 | 61.60 | 620 | 540 | 6400 |
| 3×35 + 25E | 15.10 | 17.10 | 25 | 17.10 | 48.20 – 50.70 | 64.60 | 68.40 | 690 | 780 | 7800 |
| 3×50 + 35E | 16.20 | 18.20 | 35 | 18.20 | 52.60 – 55.60 | 69.80 | 73.80 | 740 | 1110 | 9100 |
| 3×70 + 50E | 18.15 | 20.15 | 50 | 20.15 | 60.00 – 63.00 | 80.30 | 84.60 | 850 | 1560 | 12400 |
| 3×95 + 70E | 19.60 | 21.60 | 70 | 21.60 | 65.10 – 68.90 | 86.40 | 90.70 | 910 | 2000 | 14600 |
| 3×120 + 70E | 21.95 | 23.95 | 70 | 23.95 | 68.80 – 72.60 | 90.90 | 95.20 | 960 | 2000 | 16300 |
| 3×150 + 70E | 23.10 | 25.40 | 70 | 25.40 | 71.50 – 74.00 | 93.80 | 98.10 | 980 | 2000 | 18200 |
2. BS 6708 Type 331 — Current Ratings, DC Resistance, Reactance & Voltage Drop
| Phase + Earth (mm²) | Current @ 25 °C (A) | Power Cond. DC Res. (Ω/km) | Earth Cond. DC Res. (Ω/km) | Screens Parallel (Ω/km) | Armour DC Res. (Ω/km) | Reactance 50/60 Hz (Ω/km) | Min. Insul. Res. (MΩ·km) | 3-Ph Volt. Drop 50 Hz (mV/A/m) |
|---|---|---|---|---|---|---|---|---|
| 3×25 + 16E | 110 | 0.795 | 1.240 | 1.350 | 0.965 | 0.125 / 0.150 | 1250 | 1.69 |
| 3×35 + 25E | 135 | 0.565 | 0.795 | 0.800 | 0.844 | 0.117 / 0.140 | 1100 | 1.21 |
| 3×50 + 35E | 170 | 0.393 | 0.565 | 0.700 | 0.715 | 0.113 / 0.136 | 950 | 0.85 |
| 3×70 + 50E | 205 | 0.277 | 0.393 | 0.690 | 0.488 | 0.108 / 0.129 | 820 | 0.61 |
| 3×95 + 70E | 250 | 0.210 | 0.277 | 0.840 | 0.382 | 0.105 / 0.126 | 720 | 0.48 |
| 3×120 + 70E | 295 | 0.164 | 0.277 | 0.550 | 0.299 | 0.101 / 0.121 | 660 | 0.39 |
| 3×150 + 70E | 320 | 0.132 | 0.277 | 0.550 | 0.240 | 0.098 / 0.118 | 600 | 0.32 |
3. BS 6708 Type 321 (3.3 kV Unscreened Phases + Full-Size Earth) — Dimensions, Pull & Weight (35–120 mm²)
| Phase + Earth (mm²) | Phase Insul. Dia. (mm) | Earth CSA (mm²) | Earth Insul. Dia. (mm) | Inner Sheath Min–Max (mm) | Overall OD Min (mm) | Overall OD Max (mm) | Min. Bend Radius (mm) | Max. Pull (kgf) | Approx. Weight (kg/km) |
|---|---|---|---|---|---|---|---|---|---|
| 3×35 + 35E | 15.10 | 35 | 15.10 | 44.30 – 46.80 | 60.30 | 64.10 | 640 | 840 | 4900 |
| 3×50 + 50E | 16.20 | 50 | 16.20 | 51.30 – 54.30 | 68.30 | 72.30 | 720 | 1200 | 6400 |
| 3×70 + 70E | 18.15 | 70 | 18.15 | 56.40 – 59.40 | 74.40 | 78.40 | 790 | 1680 | 7700 |
| 3×95 + 95E | 19.60 | 95 | 19.60 | 63.80 – 66.80 | 84.90 | 89.20 | 890 | 2000 | 10800 |
| 3×120 + 120E | 21.95 | 120 | 21.95 | 67.50 – 71.30 | 89.40 | 93.70 | 940 | 2000 | 12300 |
4. BS 6708 Type 321 — Current Ratings, DC Resistance, Reactance & Voltage Drop
| Phase + Earth (mm²) | Current @ 25 °C (A) | Power Cond. DC Res. (Ω/km) | Earth Cond. DC Res. (Ω/km) | Armour DC Res. (Ω/km) | Reactance 50/60 Hz (Ω/km) | Min. Insul. Res. (MΩ·km) | 3-Ph Volt. Drop 50 Hz (mV/A/m) |
|---|---|---|---|---|---|---|---|
| 3×35 + 35E | 135 | 0.565 | 0.565 | 0.990 | 0.117 / 0.140 | 1100 | 1.21 |
| 3×50 + 50E | 170 | 0.393 | 0.393 | 0.760 | 0.113 / 0.136 | 950 | 0.85 |
| 3×70 + 70E | 205 | 0.277 | 0.277 | 0.530 | 0.108 / 0.129 | 820 | 0.61 |
| 3×95 + 95E | 250 | 0.210 | 0.210 | 0.400 | 0.105 / 0.126 | 720 | 0.48 |
| 3×120 + 120E | 295 | 0.164 | 0.164 | 0.320 | 0.101 / 0.121 | 660 | 0.39 |
Selection Guide: BS 6708 Medium-Voltage & Pliable Wire Armoured Cables
Compare BS 6708 Type 321/331 (1.9/3.3 kV) against 640/1100 V Type 201/211 and 3.8/6.6 kV Type 621 armoured feeders.
| BS 6708 Model | Core & Pilot Architecture, Earth Design & Primary Duty |
|---|---|
| BS 6708 Type 20 & Type 21 (640/1100V Unscreened PWA) | BS 6708 Type 20 & Type 21 (640/1100V Unscreened PWA): 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) (This Product) | 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 on BS 6708 Type 331 vs Type 321 earth sizing, 6.5 kV routine testing, and coupler compatibility.
Why does Type 321 use a full-size earth core (e.g. 95 mm² on 3×95) while Type 331 uses a reduced earth core (70 mm²)?
In BS 6708 Type 331, the three copper/nylon phase screens operate in parallel with both the Green/Yellow earth core and the pliable steel wire armour to carry earth-fault current. Because Type 321 omits individual phase screens, BS 6708 sizes the insulated earth conductor equal to the phase cross-section (35 to 120 mm²) to guarantee full earth-fault conductance.
Can BS 6708 Type 331 connect into 3.3 kV flameproof bolted mining couplers?
Yes. BS 6708 Type 331 and Type 321 are dimensionally standardized for 3.3 kV 300 A / 400 A bolted mining couplers and Ex d gate-end transformer incoming glands.
What routine dielectric voltage test is performed before shipment?
Every drum of TEBAOFLEX BS 6708 Type 321 and Type 331 undergoes a 6.5 kV AC factory high-voltage dielectric test together with conductor, screen, and pliable armour DC resistance verification.
Need BS 6708 Type 321 or Type 331 3.3 kV Armoured Cable?
Send your required type (screened Type 331 or unscreened Type 321), cross-section (25–150 mm²), and drum lengths for direct TEBAOFLEX factory pricing.
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