In motors operating at low loads, failure of any one phase causes over voltages, which
may cause rupture of insulation leading to motor burn out. Low voltage will cause
synchronous motors to come out of synchronism at 75% of rated voltage. Induction
motors may stop when voltage falls below 70%. Over voltages may occur due to
defective voltage regulator, over speeding, caused by sudden drop in load on account of
this di-electric property deteriorates. In single phase supply low voltage may cause over
load on supply cable and thermal damage to insulation of windings.