Abstract: Electric traction motors for rapid transit cars provide a first saturable reactor for sensing the current imbalance between the input and output leads of traction motor circuit, a second saturable reactor for sensing the current imbalance between the branches of the motor circuit, a current sensor in the excitation winding of each reactor to sense the current increase during a fault, a latching relay and a stepping relay both responsive to the output of each current sensor. A mode relay responsive to the dynamic braking control of the transit car connects either the sensor for the first reactor or the sensor for the second reactor to the latching and stepping relays depending upon the operating mode of the car. The latching relay functions to both disconnect the traction motors from their voltage supply and disable the car dynamic braking system upon a fault in either mode of operation. A motorman's reset button is provided to reset the latching relay after a fault to energize the motors and braking system.