Three phase cores and one pilot core, all with composite individual screens laid up around an elastomeric cradle and in contact with each other
What is BS 6708 Type 11 Trailing Cable?
Three phase cores and one pilot core, all with composite individual screens laid up around an elastomeric cradle and in contact with each other
Turkish Translation: Kompozit bireysel ekranlı üç faz ve bir kumanda damarı birbirlerine temas edecek şekilde elastomer fitil etrafında bükülür.
Introduction to BS 6708 Type 11 Trailing Cable
The BS 6708 Type 11 Trailing Cable represents a pinnacle of electrical engineering specifically designed for the demanding conditions of underground coal mining and surface quarrying operations. This specialized cable serves as the electrical lifeline for coalface cutters, shuttle cars, and similar face equipment, where reliability and safety are non-negotiable requirements.
Key Definition: BS 6708 Type 11 is a non-armoured cable featuring individually metallic screened cores with a rated voltage of 640/1100 V, specifically designed for use with coalface cutters and other similar machines in explosive atmospheres.
According to the British Standards Institution (BSI), BS 6708:1998 establishes comprehensive requirements for flexible cables used in mining and quarrying operations. The standard addresses unique challenges including explosive atmospheres containing methane gas, corrosive chemical exposure, extreme temperature variations, and mechanical stresses from heavy mobile equipment.
As documented by Amplex Mining Cable Solutions, these cables have become essential components in modern mining operations, serving applications from continuous miners and roadheaders to shuttle cars and roof bolters.
Purpose and Primary Applications
Core Operational Functions
BS 6708 Type 11 cables are engineered specifically for power supply to coalcutters and other machines operating in challenging mining environments. The cable designation indicates its capability to deliver continuous electrical power while withstanding the dynamic mechanical stresses inherent to mobile mining equipment.
Application Scenarios
Underground Mining Operations
In deep mines where explosive gases such as methane can accumulate in poorly ventilated areas, Type 11 cables provide reliable power transmission while minimizing ignition risks. The composite screening system helps manage electromagnetic interference and provides safe paths for fault currents, essential in potentially explosive atmospheres.
Surface Mining & Quarrying
Surface operations expose cables to wider temperature variations, direct rainfall, and mechanical abrasion from rocky terrain. The heavy-duty chloroprene outer sheath provides exceptional resistance to these environmental challenges.
Primary Equipment Applications:
- Excavating machines – Continuous miners, roadheaders
- Crushing machines – Mobile crushers, screening equipment
- Shuttle cars – Underground material transport
- Coalface cutters – Longwall shearers, drum cutters
- At-face equipment – Roof bolters, ventilation systems
According to research published by Reeling Cable Technology Solutions, trailing cables serve as critical lifelines for mobile mining equipment, delivering electrical power while accommodating continuous movement. The cables must balance electrical performance with mechanical durability, featuring optimized tensile strength, insulation integrity, and minimum bending radius specifications.
Cable Construction and Material Structure
Layer-by-Layer Construction Analysis
The BS 6708 Type 11 cable employs a sophisticated multi-layer construction where each component serves specific functions contributing to overall performance in demanding mining environments.
| Layer | Material/Component | Technical Specification | Function |
|---|---|---|---|
| 1. Conductor | Electrolytic Tinned Copper | IEC 60228 Class 5 | Maximum electrical conductivity with corrosion resistance |
| 2. Insulation | EPR (Ethylene Propylene Rubber) | High dielectric strength | Electrical isolation with thermal stability |
| 3. Separator | Colored Textile Tape | Color-coded identification | Core identification (Red, Yellow, Brown, Blue) |
| 4. Screen | Tinned Copper/Nylon Braid | Composite braided shield | EMI shielding and fault current management |
| 5. Lay-up | Elastomeric Cradle Configuration | All cores in contact | Mechanical stability and flexibility |
| 6. Bedding | Rubber-Based Compound | PCP rubber center | Internal cushioning and protection |
| 7. Outer Sheath | Heavy-Duty Chloroprene | Flame retardant elastomer | Environmental protection and abrasion resistance |
Conductor Technology – IEC 60228 Class 5
The conductor system utilizes electrolytic copper providing maximum electrical conductivity essential for minimizing power losses in high-current applications. According to IEC 60228 international standards, Class 5 conductors are specifically intended for flexible cables and cords, representing the most flexible stranding configuration available for general applications.
Class 5 Stranding Characteristics:
- Construction: Very fine stranded copper conductors
- Strand Count (16mm²): 126 wires × 0.40mm diameter
- Flexibility Rating: Optimized for repeated flexing without conductor fatigue
- Resistance: Maximum 1.24 Ω/km at 20°C (for 16mm² conductor)
The tinning process applied to copper conductors serves multiple purposes beyond corrosion protection. It facilitates reliable electrical connections, prevents galvanic corrosion at terminations, and extends conductor life in moisture-rich mining environments. As noted in IEC 60228 documentation, tinned wires maintain excellent contact properties even in oxidizing atmospheres.
EPR Insulation Properties
Ethylene Propylene Rubber (EPR) insulation provides superior performance characteristics critical for mining applications. According to research from the EPR Cable Technology Consortium, EPR offers significant advantages including:
EPR insulation exhibits excellent resistance to electrical tracking and treeing—common failure modes in cables exposed to contaminated mining environments. The material’s inherent flexibility ensures that the insulation system accommodates mechanical stresses from cable movement without cracking or developing weak points.
Composite Screening System
The tinned copper and nylon braided screen over phase and pilot cores provides comprehensive electromagnetic interference (EMI) shielding crucial in mining environments where multiple electrical systems operate simultaneously. This composite screening serves dual functions:
- Electromagnetic Compatibility: Reduces interference between power and control circuits
- Safety Enhancement: Provides multiple paths for fault currents, enabling protective device operation
- Mechanical Protection: Braided construction maintains flexibility while protecting inner components
Heavy-Duty Chloroprene Outer Sheath
The chloroprene (neoprene) outer sheath represents the critical environmental barrier protecting the cable from harsh mining conditions. According to Eland Cables technical documentation, chloroprene offers optimal combination of mechanical toughness and chemical resistance for mining applications.
| Property | Performance Rating | Mining Environment Benefit |
|---|---|---|
| Abrasion Resistance | Excellent | Withstands dragging over rock surfaces |
| Oil Resistance | Superior | Resists hydraulic fluids and lubricants |
| Flame Retardance | Self-extinguishing | Critical for underground fire safety |
| Ozone Resistance | Excellent | Prevents surface cracking |
| Weather Resistance | Outstanding | UV and moisture protection |
Technical Specifications and Electrical Parameters
Complete Technical Data – 3×16+16 mm² Configuration
The following comprehensive specifications represent the standard 3×16+16 mm² Type 11 trailing cable configuration, providing essential data for engineering calculations and system design.
| Parameter Category | Specification | Value | Unit |
|---|---|---|---|
| Phase Conductor | Number and Cross Section | 3 × 16 | mm² |
| Stranding Configuration | 126/0.40 | wires/mm | |
| Nominal Conductor Diameter | 5.50 | mm | |
| Nominal Insulation Diameter | 8.85 | mm | |
| Nominal Screen Diameter | 11.15 | mm | |
| Pilot Conductor | Number and Cross Section | 1 × 16 | mm² |
| Stranding Configuration | 126/0.40 | wires/mm | |
| Nominal Conductor Diameter | 5.50 | mm | |
| Nominal Insulation Diameter | 8.85 | mm | |
| Nominal Screen Diameter | 11.15 | mm | |
| Cable Details | Minimum Overall Diameter | 30.90 | mm |
| Maximum Overall Diameter | 33.00 | mm | |
| Minimum Bending Radius | 270 | mm | |
| Maximum Pulling Tension | 380 | kgf | |
| Approximate Cable Weight | 1,960 | kg/km |
Electrical Performance Parameters
| Electrical Parameter | Value | Unit | Test Conditions |
|---|---|---|---|
| Continuous Current Rating | 85 | Amperes | 25°C Ambient |
| Intermittent Current Rating | 96 | Amperes | 25°C Ambient |
| Max DC Resistance (Phase) | 1.240 | Ω/km | 20°C |
| Max DC Resistance (Pilot) | 1.240 | Ω/km | 20°C |
| Screen Resistance (4 parallel) | 1.050 | Ω/km | 20°C |
| Nominal Reactance | 0.109 | Ω/km | 50 Hz |
| Nominal Reactance | 0.131 | Ω/km | 60 Hz |
| Min Insulation Resistance | 435 | MΩ/km | 20°C |
| 3-Phase Voltage Drop | 2.62 | mV/A/m | Full Load |
Voltage Drop Calculations
The voltage drop parameter of 2.62 mV/A/m is critical for system design, particularly in long trailing cable applications. For a 100-meter cable run at 85A continuous load:
Example Calculation:
Voltage Drop = 2.62 × 85 × 100 / 1000 = 22.27 V
This represents approximately 3.5% of the 640V phase voltage, well within acceptable limits for mining equipment operation.
Compliance with International Standards
Primary Standard: BS 6708:1998
The British Standard BS 6708:1998 “Flexible cables for use at mines and quarries” establishes comprehensive requirements governing the design, construction, testing, and performance of mining cables. According to GlobalSpec Standards Database, the standard is based on National Coal Board Specifications 188, 504, and 505, representing decades of mining industry experience.
BS 6708 Type 11 Classification:
- Category: Non-armoured cables with individually metallic screened cores
- Rated Voltage: 640/1100 V
- Application: Coalface cutters and similar machines
- Configuration: Three phase cores + one pilot core with composite individual screens
Referenced International Standards
| Standard | Scope | Application to Type 11 |
|---|---|---|
| IEC 60228 | Conductors of insulated cables | Class 5 flexible conductor requirements |
| IEC 60724 | Short-circuit temperature limits | Thermal performance under fault conditions |
| BS 7655-1.2 | Insulating materials – 90°C applications | EPR insulation compound specifications |
| BS 7655-2.3 | Sheathing materials | Chloroprene sheath compound requirements |
| EN/IEC 60332-1-2 | Flame retardance testing | Single vertical flame test compliance |
BCS 188:1978 Reference
The cable design references British Coal Specification 188:1978, which established foundational requirements for trailing cables used with shuttle cars, coal cutters, and similar face equipment. This historical document represented critical safety learnings from mining operations and continues to influence modern cable design through BS 6708.
Testing and Quality Assurance
Type 11 cables undergo rigorous testing protocols including:
Comparison: BS 6708 Type 11 vs. VDE 0250 Part 812
Standards Background
Both British Standard BS 6708 and German Standard DIN VDE 0250 represent mature, internationally recognized frameworks for mining cable specifications. DIN VDE 0250 Part 812 specifically addresses EPR insulated flexible cables designated NSSHÖU, providing an interesting comparison point with BS 6708 Type 11.
According to Eland Cables VDE expertise, Germany is the only country to have issued special design regulations for flexible electrical cables covering cranes and material handling equipment, making DIN VDE 0250 globally recognized as the ultimate standard for tough rubber sheathed flexible cables.
| Parameter | BS 6708 Type 11 | VDE 0250 Part 812 (NSSHÖU) | Analysis |
|---|---|---|---|
| Rated Voltage | 640/1100 V | 450/750 V | BS 6708 higher voltage capability |
| Primary Application | Coal mining, underground operations | Heavy-duty industrial, mining tunneling | Both suited for mining |
| Conductor Standard | IEC 60228 Class 5 | DIN EN 60228 / VDE 0295 | Equivalent flexibility class |
| Insulation Material | EPR (Ethylene Propylene Rubber) | EPR or equivalent elastomer | Same base material |
| Screening | Individual composite Cu/Nylon braid | Optional screening configurations | BS 6708 mandatory EMI protection |
| Outer Sheath | Heavy-duty chloroprene (PCP) | Polychloroprene or equivalent | Comparable protection |
| Temperature Range | -40°C to +85°C | -25°C to +90°C | BS 6708 better cold performance |
| Pilot Core | Mandatory screened pilot core | Earth core configuration | BS 6708 enhanced monitoring |
| Explosive Atmosphere | Specifically designed for gassy mines | General hazardous environment | BS 6708 methane-specific design |
| Tensile Strength | 15 N/mm² permanent | 15 N/mm² (similar specification) | Equivalent mechanical rating |
Key Differentiators
BS 6708 Type 11 Advantages:
- Higher voltage rating (640/1100 V) enables powering larger mining equipment
- Mandatory composite screening on all phase and pilot cores provides superior EMI protection
- Dedicated screened pilot core enables enhanced monitoring and control functions
- Specific design for explosive atmospheres with methane gas accumulation
- Extended cold temperature capability down to -40°C for deep mine applications
VDE 0250 Part 812 Strengths:
- Global recognition as the ultimate standard for tough rubber sheathed cables
- Broader application scope including crane and material handling equipment
- Higher continuous operating temperature (90°C vs. 85°C ambient)
- Established certification network across European industrial markets
- Flexibility in screening options for various application requirements
Selection Criteria
The choice between BS 6708 Type 11 and VDE 0250 Part 812 cables depends on specific application requirements:
| Application Requirement | Recommended Standard | Rationale |
|---|---|---|
| Underground coal mining with methane risk | BS 6708 Type 11 | Specific explosive atmosphere design |
| Surface quarrying with higher voltage needs | BS 6708 Type 11 | 640/1100 V rating advantage |
| General industrial heavy-duty applications | VDE 0250 Part 812 | Broader equipment compatibility |
| Reeling cable applications | VDE 0250 Part 813 | Optimized for drum operations |
| Integrated monitoring requirements | BS 6708 Type 11 | Screened pilot core for control |
Safety Thresholds and Precautions
Critical Safety Parameters
Operating BS 6708 Type 11 cables within specified safety thresholds is essential for preventing equipment damage and ensuring personnel safety in mining environments.
⚠️ Critical Temperature Limits:
- Maximum Conductor Temperature: 90°C (continuous operation)
- Short Circuit Temperature: 200°C (maximum 5-second duration)
- Ambient Temperature Range: -40°C to +85°C
- Installation Temperature: Never install below -20°C (risk of sheath cracking)
Mechanical Safety Thresholds
| Safety Parameter | Threshold Value | Consequence of Exceeding |
|---|---|---|
| Minimum Bending Radius (Fixed) | 4 × Cable Diameter | Internal conductor stress fractures |
| Minimum Bending Radius (Flexible) | 5 × Cable Diameter | Accelerated fatigue failure |
| Maximum Pulling Tension | 380 kgf (3×16+16 mm²) | Conductor elongation or breakage |
| Permanent Tensile Force | 15 N/mm² | Permanent deformation of cable |
Explosive Atmosphere Precautions
According to Amplex Mining technical documentation, operating in potentially explosive atmospheres requires strict adherence to the following precautions:
- Regular Inspection: Visual examination for outer sheath damage that could expose conductors
- Earth Continuity Verification: Periodic testing of screening and earth path integrity
- Proper Termination: Use of approved explosion-proof connectors and glands
- Current Monitoring: Ensure operation below continuous current ratings to prevent overheating
- Protective Device Coordination: Verify relay settings for rapid fault clearing
Fire Safety Considerations
Fire represents one of the most serious hazards in underground mining. Type 11 cables incorporate specific fire safety features as documented by Reeling Cable technical resources:
Fire Safety Features:
- Flame Retardance: Compliant with EN/IEC 60332-1-2
- Self-Extinguishing: Chloroprene sheath stops burning when flame source removed
- Low Smoke Emission: Reduces visibility hazards during fire events
- Halogen-Free Options: Available configurations eliminate toxic gas emission
Installation Safety Requirements
Pre-Installation Checklist:
- Verify cable voltage rating matches system requirements
- Confirm cable cross-section adequate for load current
- Check ambient temperature within operating range
- Ensure cable routing respects minimum bending radius
- Verify earth/ground connections before energization
- Test insulation resistance (minimum 435 MΩ/km at 20°C)
- Conduct voltage withstand test at 3 kV AC
Operational Monitoring
Continuous monitoring systems should track:
- Conductor temperature via thermal sensors
- Earth continuity through pilot core monitoring
- Insulation resistance degradation trends
- Mechanical wear patterns on outer sheath
- Connection point temperature rise
Common Problems and Troubleshooting Solutions
Mechanical Failure Issues
Problem 1: Outer Sheath Damage and Abrasion
Symptoms: Visible wear, cuts, or exposure of inner components on the chloroprene sheath.
Root Causes:
- Dragging over sharp rock surfaces without adequate protection
- Improper cable chain/handler configuration
- Exceeding recommended bending radius during operation
Solutions:
- Install appropriate cable protection chains designed for mining applications
- Route cables away from identified abrasion points
- Apply removable protective sleeves at high-wear locations
- Regular inspection schedule with immediate repair of minor damage
Problem 2: Conductor Fatigue and Breakage
Symptoms: Intermittent power loss, increased resistance readings, localized heating.
Root Causes:
- Repeated flexing below minimum bending radius specifications
- Excessive tensile forces during equipment operation
- Incorrect installation with sharp bending points
Solutions:
- Redesign cable routing to maintain 5×D minimum bend radius for flexible operations
- Install tension control devices to prevent exceeding 15 N/mm² permanent load
- Replace cable chain systems causing stress concentration points
- Monitor cable flex cycles and replace before fatigue failure
Electrical Performance Degradation
Problem 3: Insulation Resistance Decline
Symptoms: Measured insulation resistance below 435 MΩ/km, increased leakage current.
Root Causes:
- Moisture ingress through damaged outer sheath
- Chemical attack on EPR insulation from hydraulic fluids
- Thermal aging from sustained overtemperature operation
- Contamination at termination points
Solutions:
- Immediate repair or replacement of damaged sheath sections
- Install cable away from known chemical exposure sources
- Monitor conductor temperature to ensure operation below 90°C
- Re-terminate connections using approved methods and materials
- Megohmmeter testing schedule (minimum monthly in harsh environments)
Problem 4: Screening Continuity Loss
Symptoms: Electromagnetic interference issues, earth fault protection malfunction.
Root Causes:
- Mechanical damage to tinned copper/nylon braid
- Corrosion at screen termination points
- Improper gland installation
Solutions:
- Verify screen resistance (should be approximately 1.05 Ω/km for 4 screens parallel)
- Clean and re-establish termination connections
- Use correct cable glands maintaining 360° screen contact
- Replace cable sections with severe braid damage
Environmental Challenges
Problem 5: Low Temperature Flexibility Loss
Symptoms: Cable becomes stiff and difficult to handle, potential cracking.
Root Causes:
- Operation below -20°C without proper material grade
- Storage in cold conditions before installation
Solutions:
- Specify cold-grade chloroprene sheath for operations below -20°C
- Pre-warm cables to above -10°C before installation in cold environments
- Increase bending radius allowances in cold temperature operations
Problem 6: Oil and Chemical Degradation
Symptoms: Swelling or softening of outer sheath, material degradation.
Preventive Measures:
- Route cables away from hydraulic equipment prone to leaks
- Clean oil contamination promptly with appropriate solvents
- Install drip trays or shields where oil exposure is unavoidable
- Specify enhanced oil-resistant compounds for severe exposure environments
Maintenance Best Practices
| Maintenance Activity | Frequency | Parameters to Check |
|---|---|---|
| Visual Inspection | Weekly | Sheath damage, abrasion, cuts, exposure |
| Insulation Resistance Test | Monthly | ≥435 MΩ/km at 20°C |
| Conductor Continuity | Monthly | ≤1.24 Ω/km per phase at 20°C |
| Screen Resistance | Quarterly | ≤1.05 Ω/km (4 screens parallel) |
| Termination Inspection | Quarterly | Temperature rise, corrosion, tightness |
| High Voltage Withstand Test | Annually | 3 kV AC for 5 minutes |
Contact Anhui Feichun Special Cable Co., Ltd.
Expert Technical Support for BS 6708 Type 11 Trailing Cables
Our engineering team provides comprehensive technical consultation for mining cable applications, including custom configurations, installation guidance, and performance optimization.
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References and Further Reading
- British Standards Institution. (1998). BS 6708:1998 – Flexible cables for use at mines and quarries. BSI Group.
- International Electrotechnical Commission. (2004). IEC 60228 – Conductors of insulated cables. IEC.
- AEI Cables Ltd. (2023). Type 11 Trailing Cable Technical Specification. Retrieved from www.aeicables.co.uk
- Amplex Mining Solutions. (2025). Understanding BS 6708 Type 11 Mining Cable. Retrieved from amplexmining.com.au
- Reeling Cable Technology. (2025). Mining Cable Technology Solutions. Retrieved from reelingcable.com
- Tratos Group. (2023). BS 6708 Standard Overview. Retrieved from tratosgroup.com
- VDE Publishing House. (1985). DIN VDE 0250-812 – Rubber insulated flexible cable NSSHÖU. VDE.
- Eland Cables. (2024). EPR Insulated Cables – Benefits and Applications. Retrieved from elandcables.com
