In addition, high efficiency and high running unity power factor allow WP motors to operate with a lower total input current, at equivalent voltage, per horsepower than any conventional induction motor available single-phase or three-phase. SPPS Written-Pole (WP) synchronous motors are highly efficient (93+%) and require a starting current that is less than two times full load running current. VFD's are also able to provide higher torque levels over short periods of time (like 150-180% for up to a minute), one reason why the supply amperage/fusing needs to be higher than the motor specifications.Let me give you an overview - in layman's terms - of our unique, large horsepower, single-phase SPPS Written-Pole® electric motors. On a lathe they are also typically have 2 mechanical speeds, on the lathe motor replacements I belt down the motor and run them to ~120 Hz, and recommend a usable speed range of 20-120 Hz. On my mill the motor covers 20-200 Hz, and 2 speed ranges of ~ 40-450 and 400-4500, i.e. So on a smaller mill with a factory installed VFD system you often will see a 2-3Hp motor used with 2 or 3 mechanical ratios. This is one reason why VFD motors are often oversized and also driven above their base speed. But you loose the 2:1 mechanical advantage if you maintained the motor's full rated speed and changed the mechanical ratio. So if you were to reduce the motor speed to say 30 Hz you loose 50% of the motor Hp, the torque is typically flat below the motor base speed.

As others as mentioned Hp is Hp be it single or 3 phase, but what is often missed is that below the motor's base speed (typically 50 or 60 Hz) you loose Hp in a linear fashion and you also loose the mechanical advantage.

10 hp single phase motor used