Technician Handbook 623 Electrical Circuit Diagnosis Voltage Voltage is electrical pressure caused by a difference in electrical charge between two points. Voltage (pressure) can exist even when electrons are not flowing. Compare voltage to water pressure. Even when water is not flowing, the pressure is there. Electrical pressure is created when electrons are freed from their atoms by friction, heat, light, pressure, chemical action, or magnetic forces. It is often called “ potential ,” because voltage has the potential to cause electrons to flow (or to do work). Voltage is measured in volts. 8 Technical Training