US Patent 7830935 Laser

A laser (10) provided with a discharge activation power supply (11) supplied with power from a 3-phase AC power line, the discharge activation power supply (11) provided inside it with three first capacitors (12a, 12b, and 12c), the laser (10) including an external ground fault protection device comprising a voltage measuring unit using the first capacitors (12a, 12b, and 12c) to measure voltages between the phases of the 3-phase AC power line and the ground and a power breaking unit (18) comparing the values of voltages measured by the voltage measuring unit and a predetermined threshold and breaking the supply of power from the 3-phase AC power line to the power supply (11) when the value of a voltage exceeds the threshold.