Loose electrical connections to motor terminals can cause voltage drop, overheating, and a chance of fire. For three-phase motors, a loose connection can cause single phasing — which will damage the motor.
The best connections are with terminal connectors (Figure 1). To attach a terminal connector to a wire, remove about ½ inch of insulation from the wire end. Insert the bare wire into the terminal connector and crimp it on with a crimping tool. Use two crimps to be sure of a good connection. With a hook type connector, be sure that tightening the terminal screw pulls the connector in rather than pushes it out of the terminal.