ENGINEERED MOBILE UNITS
TDLB – Tunnel Distribution & Lighting Box
The Tunnel Distribution & Lighting Box provides a complete solution to the Contractors in tunnel work, for temporary electrical installation, in compliance with the Local Standard Authorities where the projects are located.
In order to cope with the extreme conditions, TDLB has been developed by WE-POWER following the BS6164, that provides valuable guidance on voltages, equipment enclosures, cabling, electrical protection and lighting systems to be used in tunnels.
Dust, water and concrete casting levels require a heavy-duty steel casing and high quality components mounted inside electrical equipment, such as circuit breakers, transformers and switches, to ensure high performance and service continuity based on Health and safety rules to protect operators.
TYPICAL TUNNEL DISTRIBUTION SCHEME – 3300V
On the longest tunnels it may be necessary to step-up the voltage to 3300V at the entrance of the tunnel and step down to 400V/ 230V and 110V at regular intervals. Stepping up to 3300V requires the use of special cables and connectors but the distances that can be fed from a single source are significant (many kilometres). The usual practice is to fit 3300V “Half Couplers” to the transformers, which can be electrically interlocked. This “plug and socket” system enables the installation to be quickly extended as the tunnelling progresses.
Due to the size of 3300V switchgear, all protection for the circuit is provided at the source but the supplies to each transformer are individually protected by fuses. 3300V transformers can incorporate a single-phase 110V output to feed tunnel lighting and small power. Alternatively, dual output transformers can be incorporated to provide 400V power for larger machines as well 110V for tunnel lighting and small power.
Reduced Low Voltage limits specified in BS7671 but is greater than the 55V to earth preferred in BS6164. However, all outlets are protected by 30mA RCDs, which provide supplementary Basic protection.
The increased level of shock risk with this arrangement is minimal.