The S-Bahn Berlin is operated by Deutsche Bahn. In deviation from the usual supply of electric rail cars in Germany by overhead wires using 15 kV AC, the Berlin S-Bahn runs with a voltage of 750 volts DC, which is collected from a lateral live rail. This system is normally used only in metro systems. The network of the S-Bahn Berlin is some 330 kilometres long. Some of the outer branches reach into the surrounding districts of Brandenburg.