Alongside the overhead line, another system of power supply is distributed with the overhead line poles. At the top of the poles, there is the auxiliary power line used for all signals, level crossing protection systems, switches, switch heaters, station buildings, and yard lighting.

Where electrical power is needed, there is a transformer that lowers the voltage from the auxiliary power line's 11,000 or 22,000 volts to 230 or 400 volts.

Where auxiliary power is not available, the general power grid is utilized for these functions or, less commonly, the voltage of the overhead line is transformed down.