The PEF-301 universal automatic electronic phase switch (microprocessor based single phase automatic load transfer device)
The device serves to enhance the power supply reliability for single-phase consumers, and to protect them from inadmissible voltage faults and fluctuations. It is designed to supply industrial/ household single-phase 220-240V/50Hz load from three-phase four-wire mains 3 *  220 + N in order to maintain uninterrupted power supply of essential single-phase loads and protect them against un-allowable voltage variations in the mains. Depending on the voltage availability and quality in the main phase (the priority is set to line 1), the device selects the best healthy phase and rapidly switches the single-phase load to the phase selected. When the initial phase voltage parameters are restored, PEF-301 may switch the load back with the user defined time delay or remain operating on the line to which it transferred the load. It protects any load up to 3.5 kW – directly by means of the relay output terminals, over 3.5 kW – via magnetic contactor of appropriate rated power. PEF-301 is widely used with uninterruptible power systems in such applications as communication and telecommunication, cable TV, access control systems, countryside and suburban construction, alarm illumination and signalization schemes and a great variety of other applications (Auto transfer switch, etc).