BS7917 Fire-Resistant Offshore Cables: What Makes Them Essential in South Africa?

Introduction

In South Africa, offshore platforms, marine vessels, and industrial units operate in harsh environments where fire safety is paramount. Electrical cables, often overlooked, play a critical role in ensuring operational safety and continuity. A fire in an offshore facility or on a vessel can have catastrophic consequences, not only for personnel but also for equipment and the environment.

This is where BS7917 fire-resistant cables come into play. Developed to maintain circuit integrity under fire conditions, these cables are engineered to withstand extreme temperatures while maintaining functionality. From Cape Town’s offshore supply vessels to Durban’s oil rigs and Mossel Bay gas platforms, the adoption of BS7917 cables is becoming standard practice.

Their importance in South Africa is underscored by increasing regulatory focus on fire safety, halogen-free materials, and low smoke emissions—particularly critical in confined spaces like ships and offshore installations. This article delves into the BS7917 standard, the cable types it governs, their technical and mechanical properties, and South African case studies illustrating real-world applications.

Understanding BS7917 Standard

BS7917, titled “Elastomer-insulated fire-resistant cables for fixed wiring in mobile and fixed offshore units,” was developed to ensure circuit integrity under fire conditions. Its origins stem from the limitations of BS6883, which covers offshore cables used in lighting, power, control, instrumentation, and propulsion circuits without fire-resistant properties.

In contrast, BS7917 specifies constructional requirements and testing procedures that enable cables to maintain functionality even in the event of a fire. Key fire performance classifications include:

• F0: Fire resistance for 3 hours at 750°C

• F1: Fire resistance for 3 hours at 950°C

The design principles that make BS7917 cables fire-resistant include multiple layers of tape, halogen-free insulation, durable armouring, and specially formulated sheaths.

For South African applications, the importance of halogen-free and low smoke emission cannot be overstated. Mines, offshore rigs, and industrial plants all benefit from reduced toxic gas emissions during fire incidents, protecting both personnel and equipment.

BS7917 is often used alongside BS7919, which covers medium-voltage fire-resistant cables, and complements BS6883, forming a comprehensive framework for offshore cable safety.

Overview of BS7917 Cable Types

BS7917 cables are classified according to outer sheath type and duty level. The three primary categories are:

1. SW2: Heavy-duty, enhanced oil-resistant, flame retardant with reduced halogen gas emission. Ideal for critical power circuits.

2. SW3: Ordinary duty, oil-resistant, low smoke and corrosive gas emission. Suitable for standard power and control wiring.

3. SW4: Ordinary duty, enhanced oil-resistant, low smoke and gas emission. Designed for flexible multi-core installations.

Each type balances mechanical durability, oil resistance, and fire performance to suit different operational needs.

Detailed Specifications of Key Cables

TCu/MGT/EPR/CS/ZH/GSWB/ZH 150/250V Cable

Applications: Fixed wiring in ships and offshore units where fire safety is critical.

Construction:

• Conductor: Class 5 tinned copper

• Insulation: Halogen-free EPR

• Separator: Mica glass tape

• Screen: Collective aluminium polyester tape

• Bedding: Halogen-free elastomer

• Armour: Galvanized steel wire braid (GSWB)

• Sheath: Halogen-free, heat and oil resistant elastomer

Electrical & Mechanical Properties:

• Voltage rating: 150/250V

• Temperature: -40°C to +90°C

• Minimum bending radius: 6x overall diameter

• Typical conductor resistance: 13.7–26.7 Ω/km depending on size

• Ampacity: 15–339A depending on cores and cross-section

South African Case Study:
A Cape Town-based offshore supply vessel underwent retrofitting to comply with fire safety regulations. SW2 150/250V cables were installed in all critical power circuits, enhancing fire resilience while maintaining operational continuity.

TCu/MGT/EPR/IS/ZH/GSWB/ZH 150/250V Cable

Applications: Fire-resistant fixed wiring for ships and offshore installations, including instrumentation and control circuits.

Construction Differences:

• Individual screening for sensitive instrumentation

• Class 2 stranded conductors for sizes >2.5mm²

• Enhanced bending radius: 10x overall diameter

Electrical & Mechanical Properties:

• Voltage rating: 150/250V, test voltage 1.5kV

• Temperature range: -40°C to +90°C

• Ampacity and resistance values similar to SW2, adjusted for individual screening

South African Case Study:
On a Durban offshore oil rig, IS-type BS7917 cables were installed for fire-resistant instrumentation wiring. The individual screening ensured minimal electromagnetic interference, crucial for accurate sensor readings during critical operations.

TCu/MGT/EPR/ZH/GSWB/ZH 0.6/1kV SW4 Cable

Applications: Fixed wiring up to 1kV in ships and offshore units, including main power circuits.

Construction:

• Conductor: Class 5 flexible or Class 2 stranded tinned copper depending on size

• Insulation: Halogen-free EPR Type GP4

• Bedding: Halogen-free elastomer Type SB1

• Armour: GSWB

• Sheath: Type SW4, flame retardant

Electrical Ratings:

• Voltage rating: 0.6/1kV

• Ampacity: Varies from 7–339A depending on core number and cross-section

• De-rating factors applied for ambient temperatures up to 80°C

South African Case Study:
At a Mossel Bay offshore gas platform, SW4 0.6/1kV cables were used for main power circuits. Fire integrity tests confirmed that circuits remained operational under simulated fire conditions, demonstrating compliance with BS7917 and enhancing crew safety.

Electrical and Mechanical Properties

BS7917 cables provide detailed specifications for electrical and mechanical properties:

• Ampacity tables for single, 2-core, 3–4-core, and multi-core configurations

• Maximum insulation resistance, inductance, and capacitance

• L/R ratios at 1kHz for accurate impedance characterization

• De-rating factors for high ambient temperatures common in South African offshore environments:

Comparing SW2, SW3, and SW4, SW2 offers the highest mechanical and fire performance, SW3 is optimized for cost-sensitive standard circuits, and SW4 balances flexibility with fire resistance for multi-core installations.

Fire Resistance and Safety Performance

BS7917 ensures compliance with F0 (750°C) and F1 (950°C) fire ratings, maintaining circuit integrity for at least 3 hours under extreme conditions.

• Low smoke and halogen-free materials protect personnel from toxic gas inhalation.

• Reduced corrosive emissions preserve sensitive electronic equipment.

Practical Scenario:
During a fire drill on a South African offshore platform, SW4 cables continued to operate critical communication and power circuits while nearby conventional cables failed, validating the efficacy of BS7917 in harsh conditions.

Installation Considerations

When installing BS7917 cables, careful attention is required:

• Bending radius: Maintain minimum 4–10x overall diameter depending on type and cross-section

• Mechanical protection: Armour and sheaths must be handled to prevent abrasion

• Jointing & termination: Use compatible fire-resistant materials

• Environmental factors: High humidity, saltwater exposure, and elevated temperatures in South African offshore regions must be considered

Correct installation preserves both fire-resistant and mechanical performance.

Common Questions and Answers (FAQ)

1. Can BS7917 cables be used in underground mining?
   While primarily designed for offshore and marine environments, they can be used in mining where fire integrity is critical.

2. What is the difference between SW2, SW3, and SW4?
   SW2 is heavy-duty, SW3 is ordinary duty, and SW4 is ordinary duty with enhanced flexibility and multi-core support.

3. Are these cables suitable for high-voltage applications above 1kV?
   No, BS7917 cables are typically rated up to 1kV. Higher voltage applications require BS7919 or other standards.

4. How do halogen-free materials affect fire safety?
   They reduce toxic gas and smoke emissions, protecting personnel and equipment.

5. How to select the right conductor size for offshore installations?
   Based on ampacity tables, circuit load, ambient temperature, and derating factors.

6. How are these cables tested for fire resistance?
   Through BS7917-mandated fire tests at 750°C (F0) and 950°C (F1) for 3 hours.

7. Can South African suppliers provide locally certified BS7917 cables?
   Yes, several suppliers in Cape Town, Durban, and Mossel Bay provide BS7917-compliant cables.

8. Maintenance tips:
   Regular inspection for mechanical damage, proper termination, and avoiding excessive bending or abrasion.

South African Case Studies

Case Study 1: Cape Town Offshore Supply Vessel

• Retrofit with SW2 150/250V cables

• Enhanced crew safety and compliance with fire regulations

Case Study 2: Durban Offshore Oil Rig

• Installation of IS-type 150/250V cables for instrumentation

• Ensured minimal interference and fire-resistant integrity

Case Study 3: Mossel Bay Gas Platform

• SW4 0.6/1kV cables for main power circuits

• Fire drill tests confirmed operational integrity during simulated fires

Lessons Learned: Compliance with BS7917 ensures both fire safety and operational continuity, critical in South African offshore environments.

Summary & Recommendations

BS7917 cables provide fire resistance, halogen-free insulation, flame retardancy, and low smoke emission, making them essential for offshore and marine operations in South Africa. Key takeaways:

• SW2 – Heavy-duty, critical circuits

• SW3 – Ordinary duty, cost-effective standard circuits

• SW4 – Flexible, multi-core, main power circuits

For South African engineers and installers:

• Prioritize fire-resistant, halogen-free cables in critical circuits

• Consider local environmental conditions when selecting cables

• Future trends: Integration with smart monitoring systems for real-time fire safety and circuit integrity

The adoption of BS7917-compliant cables in South Africa ensures safety, compliance, and operational reliability in challenging offshore, marine, and industrial environments.

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

WhatsApp Contact:

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

+86 17333223430