Melbourne's tram system operates on 600 volt DC electricity, provided to the over head lines by a network of 60 (as Of March 2021) substations spread across the network. Electricity is supplied to these substations in either 6,600, 11,000, or 22,000 volt AC and is then stepped down, and rectified to 600 volt DC. The overhead system is further separated into 100 sections, this is done for two reasons, one is to maintain voltage and current across the network, and two is to isolate disruptions when issues relating to the electrical transmission system occur. The most common disturbances to the supply system are over height vehicles, falling tree limbs, damaged poles, and fires nearby to overhead wires.