Abstract: An electrical device is connected to the magnetic starter of an electrical motor to protect the motor windings from a loss of power on one or more input lines of a three phase power source. The device includes two transformers each being connected across two input lines and having one input line in common with each other. The transformer secondaries are each connected in a relay circuit so that a voltage on the secondary of each transformer above a predetermined value will actuate the relay in its respective circuit. The contacts of both relays are connected in series with each other and with the magnetic starter of the electrical motor so as to actuate the magnetic starter when both relays are closed. When the voltage on any of the three input lines drops substantially below a normal operating level, one or both of these relays will open, immediately turning off the magnetic starter and shutting down the motor to prevent damage to the motor windings.