Automatic Change Over Contactors ( automatic transfer switches ) for emergency power and normal power changeover Features : -sufficient contact open time to avooid possible arcing during changeover -contact pressure is kept constant by leaf spring and therefore no change in contact conductivity due to voltage fluctuations -no operating current required after the changeover because of the mechanical latch mechanism -contact ara made from silver alloy for high resistance to burn-off - self sliding contact clean dust and oxidation on contact' s each time when the contactor is operated