During start-up, the torque and starting current are reduced to 1/3 of their nominal values, in which case Gates A39 an engine can only start with a star-delta key when its torque on the star connection is greater than of the axle load. Due to the low starting torque to which the engine is contained, the star-triangle wrenches are more appropriately used in starter motors. In industrial electrical installations, especially those overloaded, star-delta switches can be applied as a way to soften the starting effects of the electric motors.
It will only be possible to start an electric motor with star-delta switches if it has six accessible terminals and has a nominal double voltage, such as 220/380 V or 380/660 V. Initially the procedure for motor starting is done connecting it in the star configuration until it achieves a velocity close to the regime velocity, when this connection is undone and the triangle connection is made. Switching of the connection during start-up is followed by a rise in current, so that the advantages of reducing it are added if the switching is anticipated from the ideal point.