I did not see any hp figure on the nameplate, but if it is indeed a 1/2 hp, then 1.8 A does correspond with single phase. I don't recall ever seeing a 1/2 hp three phase motor, so it seems you have a single phase motor. To answer yuor other questions: A 3-phase motor is usually only three wires. The only time you will see 4 wires in a 3-phase supply system is when they bring the common node out for purposes of ground-fault detection, or if phase to neutral voltage is needed -- not applicable here. You can try placing the motor conductors across 220/240 V single phase and see if it works. If the motor comes up to speed quickly, then you have a single phase motor. If she hums, staggers and seems reluctant, then you may have a 3-phase motor, or maybe a defective motor. As for the drum switch connected green wire, it may be that the green wire is wired to permit reverse rotation. Look at the drum switch and try and trace the conductors. If reverse rotation position corresponds with a connection to the green wire, it may explain the 3rd conductor.