The D3/LLI Live Line Indicator is a resistive type voltage detector designed for use on overhead a.c. rail electrification systems are operating at 25kV nominal voltage. The ‘LLI’ threshold is specified as 12kV ± 5%; however, it should be noted that induced voltages could reach 10kV.
The unit is designed to be mounted on approved fibreglass earth poles with the pole immediately below the indicator being the primary insulator (ref EFT-17451 – 0091/012470). The signal emitted by the D3/LLI is both audible and visible. Power is provided by a rechargeable battery, housed within the central unit. The battery can be charged in situ using the charger supplied.
The D3/LLI comprises a central unit and a contact probe. The contact is manufactured from lightweight fibreglass tubing and houses the calibrated resistor stack. The pole section is foam-filled to increase the voltage that it can withstand. The probe is connected to the overhead line by an aluminium hook.
The top of the pole is coated in a special high reflectivity paint to ease visibility when applying the indicator in poor lighting conditions, and a limiting collar is fitted to demark the limit of any electrified lines. The Earth connecting lead is designed to fuse should the unit be misused by applying the main unit directly to traction current and the cable is housed in a protective jacket to shield the operator.