Motor protective device

Apparatus for protecting an electrical motor having a magnetic starter and connected to a three phase power source from a loss of power on one or more input lines of said source, comprising:

• a first transformer having a first primary winding connected across first and second input lines;
• a second transformer having a second primary winding connected across said second input line and a third input line;
• a first relay having a first coil and a first switch actuable by the first coil, the first coil being connected to the secondary winding of the first transformer;
• and
• a second relay having a second coil connected to the secondary winding of the second transformer and having a second switch actuable by the second coil connected in series with the first switch of the first relay;
• said first and second relays being adapted for connection in series with the magnetic starter of the motor to actuate and deactuate the starter.

Apparatus for protecting an electrical motor connected to a three phase power source from a power loss on one or more input lines of said source, comprising:

• a first transformer having a first primary winding connected across first and second input lines;
• a second transformer having a second primary winding connected across said second input line and a third input line;
• a first relay having a first coil and a first pair of contacts actuable by the first coil, the first coil being connected to the secondary winding of the first transformer;
• a second relay having a second coil connected to the secondary winding of the second transformer and having a second pair of contacts actuable by the second coil connected in series with the first pair of contacts of the first relay;
• and
• a magnetic starter for a three phase motor having a starter coil connected in series with the first and second pairs of contacts and having a contactor actuable by the starter coil to connect the three phase inputs of the motor to the input lines of the three phase power source.

Apparatus for protecting an electrical motor having a magnetic starter and connected to a three phase power source from a loss of power on one or more input lines of said source, comprising:

• a first transformer having a first primary winding connected across first and second input lines;
• a second transformer having a second primary winding connected across said second input line and a third input line;
• said first and second primary windings being each split into two sections for connecting to the three phase power source in series with each other to accommodate a 480 volt power source or in parallel with each other to accommodate a 240 volt source;
• the secondary windings of said first and second transformers being each wired to provide about a 200 volt output signal with the respective primaries of said first and second transformers being wired in series to accommodate a 480 volt power source or in parallel to accommodate a 240 volt power source;
• a first relay having a first coil and a first switch actuable by the first coil, the first coil being connected to the secondary winding of the first tranformer;
• and
• a second relay having a second coil connected to the secondary winding of the second transformer and having a second switch actuable by the second coil connected in series with the first switch of the first relay;
• said first and second relays being adapted for connection in series with the magnetic starter of the motor to actuate and deactuate the starter;
• said first and second relays each have switches oriented to deactuate when the voltage on the secondary windings of said first and second transformers respectively is half or less of the normal operating voltage.