Specifications of the electrical distribution box for the Mali tunnel

Electrical distribution boxes for the Mali tunnel are designed to provide reliable, safe, and flexible power distribution under harsh tunnel conditions, complying with BS6164, IEC standards, and local Malian regulations.

General Design Requirements

Tunnel distribution boxes must withstand extreme conditions such as dust, water ingress, and concrete casting. Heavy-duty steel enclosures are used to protect internal components, including circuit breakers, transformers, and switches, ensuring continuity of service and operator safety . The design must allow for modular expansion as tunneling progresses, often using plug-and-socket mechanisms for quick installation and interconnection .

Voltage and Power Configuration

• High Voltage Input: For longer tunnels, power may be stepped up to 3300 V at the entrance and stepped down to 400 V / 230 V and 110 V at intervals .
• Transformers: 3300 V transformers can provide dual outputs, supplying 400 V for heavy machinery and 110 V for lighting and small equipment .
• Low Voltage Distribution: 400 V supplies feed heavy plant, conveyors, compressors, pumps, and fans, with industrial socket outlets rated 16A, 32A, 63A, and 125A, each protected by circuit breakers and RCDs .

Safety and Protection

• Circuit Protection: Each transformer output is individually fused, and high-voltage switchgear is protected at the source .
• Earth Continuity Monitoring: High-current connectors (63A and 125A) include pilot pins to ensure proper grounding .
• Fire and Mechanical Protection: Electrical installations critical for safety, such as emergency lighting, fire detection, and communication systems, must be protected against mechanical impact, heat, and fire .
• Emergency Power: Systems must include alternative power sources (UPS or diesel generators) to maintain critical operations during main supply failure .

Compliance and Standards

• Local Regulations: Installations must comply with Malian concession requirements and road regulations for public domain works .
• International Standards: In the absence of national standards, IEC and BS6164 standards are referenced for voltages, enclosures, cabling, and protection systems .
• Cable Requirements: Low flammability, low smoke, and low toxicity cables (B2CA, s1a, a1) are used to meet safety and fire regulations .

Installation and Operational Considerations

• Modular and Extendable: Distribution boxes are designed for plug-in connections to allow relocation as tunneling advances .
• Lighting Integration: Tunnel lighting is powered via 110 V outputs, often integrated into handrails or walkways to maintain minimum illuminance of 1 lux at walkway level .
• Maintenance: Only certified operators or concession holders may maintain or modify interior installations, ensuring compliance with safety and operational standards . These specifications ensure that the Mali tunnel's electrical distribution system is robust, safe, and adaptable, providing reliable power for both construction and operational phases while meeting local and international safety standards.