Time delay fuses comprise one group of devices which function to provide motor overload protection. The fuse is rated for 125 to 150 percent of normal running current. Only time delay fuses allow momentarily high startup currents a chance to clear before tripping the device. If the motor becomes overloaded and the operating current reaches the fuse trip level, the power supply is interrupted. For three phase motors, some form of single phasing protection is required to switch off the power in cases where only one fuse blows on a three phase circuit.