BS 6708 Type 20 & 21 Mining Cables: South Africa’s Heavy-Duty Power Solution

Introduction

In the heart of South Africa’s mining and quarrying industry, where machinery moves tons of ore daily, the reliability of power supply can make or break operational efficiency. Flexible trailing cables are the unsung heroes of these operations, transmitting electricity to heavy-duty equipment under harsh conditions—dust, moisture, abrasion, and constant mechanical stress.

Enter BS 6708 Type 20 and Type 21 cables, British Standard-designed trailing cables optimized for the rigorous demands of South African mines. Known for their flexibility, durability, and compliance with local regulatory frameworks, these cables form the backbone of underground gold mines in Gauteng and platinum operations in Rustenburg.

This article dives deep into BS 6708, exploring the differences between Type 20 and Type 21 cables, their technical specifications, applications, and real-world performance in South African mining conditions.

Understanding BS 6708: The Standard for Flexible Mining Cables

BS 6708 is a British Standard that specifies the design, testing, and performance requirements for flexible trailing cables used in mining and quarrying applications. Its primary goal is to ensure electrical safety, mechanical durability, and operational reliability under extreme conditions.

Historical Context:
Originally developed for the UK mining sector, BS 6708 quickly gained international recognition for its comprehensive approach to cable safety. In South Africa, mines adopted the standard to reduce operational downtime and ensure compliance with the National Regulator for Compulsory Specifications (NRCS).

Key Requirements Under BS 6708:

• Voltage Rating: Typically 640/1100V for heavy-duty machinery.

• Mechanical Flexibility: Ability to bend and withstand repeated movement without damage.

• Durability: Resistance to abrasion, oil, chemicals, and environmental stress.

• Insulation Standards: Use of EPR (Ethylene Propylene Rubber) or equivalent materials for reliable performance.

Cables Under BS 6708:

• Type 20: 3-core heavy-duty cable.

• Type 21: 4-core heavy-duty cable including a neutral conductor.

• Other Trailing Cables: Designed for various voltages and applications.

The significance of BS 6708 in mining operations cannot be overstated—it ensures equipment uptime, worker safety, and compliance with South African regulations.

BS 6708 Type 20 Cable

Applications

Type 20 cables are typically deployed for heavy-duty 3-core machinery, such as:

• Excavators

• Crushers

• Conveyor belts

South African Case Study:
At a gold mine in Gauteng, Type 20 cables supply power to underground crushers operating in dusty, high-abrasion conditions. Their flexibility allows rapid relocation as mining faces shift, reducing downtime and maintenance costs.

Advantages:

• Excellent resistance to mechanical wear

• Ideal for mobile machinery

• Handles high abrasion environments efficiently

Construction & Materials

The construction of Type 20 cables reflects its rugged design:

• Conductor: Electrolytic, stranded, tinned copper wire (IEC 60228 Class 5).

• Insulation: EPR (Ethylene Propylene Rubber) for thermal stability and chemical resistance.

• Layup: Cores laid over a cradle without contacting each other, minimizing electrical interference.

• Bedding: Rubber-based for shock absorption.

• Armour: Pliable galvanized steel to withstand crushing and abrasion.

• Outer Sheath: Heavy-duty chloroprene for environmental protection.

Diagram Suggestion: A cross-sectional schematic highlighting the conductor, insulation, bedding, armour, and outer sheath layers.

Technical Specifications

Electrical Performance

Type 20 cables are designed to handle continuous heavy loads:

• Current Rating: 28–320 A at 25°C ambient

• DC Resistance: Phase conductors 0.132–8.21 Ω/km, armour 0.45–4.6 Ω/km

Real-World Performance:
In the Gauteng gold mine, Type 20 cables sustained continuous operation for 18 months under high-load conditions, showing minimal insulation degradation and zero unplanned downtime.

Key Advantages & Limitations

Advantages:

• High mechanical and chemical resistance

• Flexible in dynamic operations

• Long service life under extreme conditions

Limitations:

• Heavier and larger diameters reduce portability

• Requires careful installation to avoid bending stress

BS 6708 Type 21 Cable

Applications

Type 21 is a 4-core cable, including a neutral conductor, used for:

• Multi-phase heavy machinery

• Conveyor systems

• Equipment requiring balanced power supply

South African Case Study:
At a Rustenburg platinum mine, Type 21 cables power multi-phase conveyor belts. The neutral conductor ensures even load distribution and prevents phase imbalance, reducing downtime and extending equipment life.

Advantages:

• Suitable for complex power systems

• Reliable neutral distribution

• Enhanced operational safety

Construction & Materials

Type 21 shares similar construction to Type 20, with the key difference being the inclusion of a neutral conductor:

• Conductor: Stranded tinned copper, IEC 60228 Class 5

• Insulation: EPR

• Layup: Cores laid without contacting each other

• Bedding: Rubber

• Armour: Pliable galvanized steel

• Outer Sheath: Chloroprene

Technical Specifications

Electrical Performance

• Current Rating: 28–320 A at 25°C

• DC Resistance: Phase conductors 0.132–8.21 Ω/km, armour 0.41–4.2 Ω/km

Field Performance:
Rustenburg conveyor systems using Type 21 experienced improved load balance, reducing electrical faults by 15% compared to previous non-compliant trailing cables.

Advantages & Limitations

Advantages:

• Reliable for complex machinery

• Neutral conductor prevents imbalance

• Durable under harsh mining conditions

Limitations:

• Slightly heavier than Type 20

• Requires more storage space and careful handling

Comparative Analysis: Type 20 vs Type 21

Case Recommendation:
For a new underground copper mine, where machinery requires a neutral for balanced load, Type 21 is preferred. Type 20 is ideal for simpler 3-core equipment.

Installation Guidelines & Handling Tips

• Always respect the minimum bending radius.

• Store cables on clean, dry reels; avoid sharp edges.

• Uncoil gradually to prevent kinks.

• Protect from chemical spills and abrasion.

• Regularly inspect for cuts, cracks, or armour damage.

• Consider South African climate: underground humidity and seasonal temperature variations can affect insulation longevity.

Safety Considerations & Compliance

BS 6708-compliant cables ensure:

• Mechanical robustness

• Insulation integrity

• Fire resistance

NRCS Compliance:
South African regulations require certified trailing cables. Non-compliant cables risk fines, downtime, and safety hazards.

Electrical Safety Practices:

• Proper earthing

• Overload protection

• Emergency response planning

Common Issues & FAQs

Q1: Can Type 20/21 cables be spliced underground?
A: Not recommended—splicing compromises mechanical integrity and compliance.

Q2: Lifespan in high-abrasion environments?
A: Typically 5–8 years, depending on load cycles and maintenance.

Q3: How to detect insulation or armour damage?
A: Regular visual inspection and insulation resistance testing.

Q4: Electrical testing frequency?
A: At least annually, more frequently in heavy-duty operations.

Q5: Can Type 21 replace Type 20?
A: Yes, but may be heavier and less flexible.

South African Incidents:
A Gauteng mine reported downtime due to improper Type 20 splicing—reinforcing the importance of adhering to installation standards.

Real-World South African Case Studies

Gauteng Gold Mine (Type 20):

• Application: Underground crushers

• Outcome: Increased operational efficiency, minimal cable failures over 18 months

Rustenburg Platinum Mine (Type 21):

• Application: Conveyor systems

• Outcome: Reduced downtime, improved safety, better load balance

Lessons Learned:

• Correct cable specification is critical

• Adherence to installation and maintenance practices ensures longevity

Future Trends & Innovations

• LSZH Alternatives: Safer cables with low smoke and halogen-free properties.

• Smart Trailing Cables: Embedded sensors for temperature, current, and real-time fault detection.

• Energy Efficiency: Materials and design improvements reduce power losses.

• Mining Modernization: Smart cables enable predictive maintenance, reducing downtime and costs.

Conclusion

BS 6708 Type 20 and Type 21 cables remain the gold standard for heavy-duty mining power supply in South Africa. Their robust construction, compliance with safety standards, and proven field performance ensure operational efficiency in harsh mining conditions.

Choosing the right cable type, following proper installation, and performing regular maintenance are not just best practices—they are essential for safe and productive mining operations. South African mines that prioritize these principles benefit from reduced downtime, enhanced safety, and improved long-term profitability.

BS 6708 Type 20 and Type 21 cables: power reliability you can count on, underground or above.

Contact Anhui Feichun Special Cable Co., Ltd.

For comprehensive technical specifications and quotations, please contact our specialized mining cable engineering team:

Technical Engineering Support:

tech@feichuncables.com

Sales Engineering Department:

Li.wang@feichuncables.com

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Manufacturer: Anhui Feichun Special Cable Co., Ltd. (安徽飞纯特种电缆有限公司)

Manufacturing Headquarters: Building A, Private Science and Technology Park, Hefei Economic and Technological Development Zone, Anhui Province, People’s Republic of China

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