From an ITT motor manual loaned to me by an educated professional! Im a dummy, so this is all from the manual only!!! 3-wire prose and cons Pro-Capacitor start assures starts under severe circumstances, such as an excessively deep well, or excessice static head. More torque is provided at the motor for hard to start situations Capacitor run assures smoother running, lower current and lower running temp All starting components are located above ground, and though the potential for failure is greater, the components can be easily and cheaply accessed and repaired or replaced General electrical consumption can be lower, or greater, depending on depth of well and distance from pump to controller Cable requires an extra supply lead, but the cable can be lighter in guage Cons-capacitors can and do fail as time weakens the internal construction of these devices Relay is not sealed from atmospheric pressure, hence contacts can oxidize from repeated arcing Cable requires an extra supply lead, and though the cable can be lighter in guage, the weight is 1/4 to 1/3 more, and the added expense can be much greater Under residential useage and average installations, starting current consumption may actually be higher due to required setbacks and distance of control box from well 2-wire pros and cons pros-Starting components are all located within the hermatically sealed stator housing of the motor Installation is much simpler No potential start relay to fail or complicate day to day operation No capacitors are used except in some limited designs, and where used, sealed components provide extra protection so the potential for failure of these components may be reduced greatly or may not exist alltogether Internal starting switch is sealed from any contact with oxygen so arcing from normal use will not cause contacts to oxidize and fail Internal starting switch and lack of one way capacitors can provide pulsed starting torque to prevent motor jambing due to sand mud or other restrictions Cable is simpler, lighter, and economical to purchase and to instal Motor starts softer, decreasing shock loading of pump components ConsIf starting components fail (highly unlikely) motor must be pulled and replaced Requires a better eye and closer tolerance for resistance measurements Lower starting torque under severe static head. this is the reason that higher horsepower pumps are currently 3 wire Operating temp of motor is slightly higher but this should not apply except under abusive circumstances *The severe conditions as stated above very rarely apply to the normal residential homeowner. The preference of 2 wire or 3 wire motors is usually a matter of taste for aplications below 1.5 hp. and a 2 wire is always recommended for these installations due to simplicity, cost advantages, and obvious maintenance reduction and extended life of starting components. Refer back to the pioneer days of the electronic semiconductor as all major devices were embrasing the new technological advances of the solid state semiconductor. Time only can prove the advantages of the new over the old.