Prestriking voltages associated with motor breaker closing

Steep-fronted surges arriving at motor terminals due to breaker closing result from the prestrike voltages present across each breaker pole as an arc is established. This prestrike voltage has been shown to depend on the instantaneous 60 Hz source voltage, and transients transferred through the motor from poles already closed, and the dielectric withstand of the closing contact gap. The worst-case prestrike voltage reaches a higher value than previously reported. Statistical studies show that a motor is likely to be stressed within a few percent of the maximum surge level, if switched daily over 30 years.>