TRANSFER SWITCH sEctioN 3.1DEscriPtioN & comPoNENtsPart 3Page 57tranSFer mechaniSmThe 2-pole transfer mechanism consists of a pairof moveable LOAD contacts, a pair of stationaryUTILITY contacts, and a pair of stationary STANDBYcontacts. The load contacts can be connected tothe utility contacts by a utility closing coil; or to thestandby contacts by a standby closing coil. In addi-tion, the load contacts can be actuated to either theUTILITY or STANDBY side by means of a manualtransfer handle. See Figures 2 and 3.STANDBYLOADUTILITYFigure 2. Load Connected to Utility Power SourceSTANDBYLOADUTILITYFigure 3. Load Connected to Standby Power SourceUTILITY CLOSING COIL C1:See Figure 4. This coil is energized by rectified util-ity source power, to actuate the load contacts to theUTILITY power source side. When energized, the coilwill move the main contacts to an “overcenter” posi-tion. A limit switch will then be actuated to open thecircuit and spring force will complete the retransfer toSTANDBY. A bridge rectifier, which changes the utilitysource alternating current (AC) to direct current (DC),is sealed in the coil wrappings. If coil or bridge rectifierreplacement becomes necessary, the entire coil andbridge assembly should be replaced.STANDBY CLOSING COIL C2:Coil C2 is energized by rectified standby sourcepower, to actuate the load contacts to their “Standby”source side. Energizing the coil moves the load con-tacts to an overcenter position; limit switch action thenopens the circuit and spring force will complete thetransfer action to “Standby”. This coil’s bridge rectifieris also sealed in the coil wrappings. Replace the coiland bridge rectifier as a unit.LIMIT SWITCHES SW2 AND SW3:Switches are mechanically actuated by load contactsmovement. When the load contacts are connected tothe utility contacts, limit switch SW2 opens the utilitycircuit to utility closing coil C1 and limit switch SW3closes the standby circuit to standby closing coil C2.The limit switches “arm” the system for retransferback to UTILITY when the load contacts are con-nected to the STANDBY side. Conversely, when theload contacts are connected to the UTILITY side, theswitches “arm” the system for transfer to STANDBY.An open condition in limit switch SW2 will preventretransfer to “Utility”. An open switch SW3 will preventtransfer to STANDBY.UTILITYCLOSINGCOIL (C1)STANDBYCLOSINGCOIL (C2)BRIDGERECTIFIERBRIDGERECTIFIERMANUALTRANSFERLEVERLIMITSWITCH(SW2)N1N2E2E1T1LIMITSWITCH(SW3)T2N2A AAB126205BE2Figure 4. The “W/V-Type” Transfer MechanismtranSFer relayTransfer relay operation is controlled by a circuitboard. That circuit board is a part of a control panelassembly, mounted on the standby generator set.Figure 5 shows the transfer relay pictorially andschematically. Relay operation may be brieflydescribed as follows:1. Generator battery voltage (12 volts DC) is available tothe transfer relay coil from the generator circuit board,via Wire 15B and Relay Terminal A.a. The 12 volts DC circuit is completed throughthe transfer relay coil and back to the generatorcircuit board, via Wire 23.b. Circuit board action normally holds the Wire23 circuit open to ground and the relay isde-energized.0G9266revA.indd 57 10/15/2008 11:27:24 AM
