Dual voltage input of 120/277 VAC 60 Hz. includes a fully automatic constant voltage, current limited charger with transformer isolation and low battery voltage disconnect. transfer contact through electric relay. power distribution made with fused leads through internally located distribution board. maximum power consumption of 20 watts (all models). test initiated by means of integral test switch. AC-on indicated by LED. AC lock out provision prevents discharge of battery at installation until power is present.