This is a list of the power supply systems that are, or have been, used for railway electrification. Note that the voltages are nominal and vary depending on load and distance from the substation. Many modern trams and trains use on-board solid-state electronics to convert these supplies to run three-phase AC traction motors. Tram electrification systems are listed here. Key to the tables below Volts: voltage or volt Current: DC = direct current # Hz = frequency in hertz (alternating current (AC)) AC supplies are usually single-phase (1Ø) except where marked three-phase (3Ø). Conductors: overhead line or conductor rail, usually a third rail to one side of the running rails. Conductor rail can be: top contact: oldest, least safe, most affected by ice, snow, rain and leaves. Protection boards are installed on most top contact systems, which increases safety and reduces these affections. side contact: newer, safer, less affected by ice, snow, rain and leaves bottom contact: newest, safest, least affected by ice, snow, rain and leaves Systems using standard voltages Voltages are defined by two standards: BS EN 50163 and IEC 60850. Overhead systems 600 V DC 750 V DC 1,200 V DC 1,500 V DC 3 kV DC AC, Hz / AC, AC, Conductor rail systems 600 V DC conductor All systems are third rail unless stated otherwise. Used by some older metros. 750 V DC conductor Conductor rail systems have been separated into tables based on whether they are top, side or bottom contact. Used by most metros outside Asia and the former Eastern bloc. Bottom contact Side contact Top contact Mixed 1,200 V DC conductor All systems are third rail and side contact unless stated otherwise. 1,500 V DC conductor All systems are third rail unless stated otherwise. Systems using non-standard voltages Overhead systems DC voltage AC voltage Three-phase AC voltage Two wires Three wires Conductor rail systems (DC voltage) Conductor rail systems have been separated into tables based on whether they are top, side or bottom contact. Top contact systems Side contact systems All third rail unless otherwise stated. Bottom contact systems All third rail unless otherwise stated. Conductor rail systems (AC voltage) Special or unusual types DC, plough collection from conductors in conduit below track London County Council Tramways, later operated by London Transport streetcars in New York City (Manhattan), New York Washington, D.C. streetcars Panama Canal locks' ship handlers (called mules) DC, one