The maximum motor size to be operated single-phase at 120 volts alternating current (VAC) via an across the line starter is ¾ horse power (HP).
The maximum motor size to be operated single phase at 240 VAC via an across the line starter is 2 horse power.
The maximum motor size to be operated single phase at 240 VAC using a capacitor, repulsion induction, or repulsion start motor starter is 7 ½ horse power.
Any single phase motors larger than those listed above will require the use of a variable speed drive or some other type of soft start.
3 phase motors, 10 horsepower to 75 horsepower inclusive, shall be provided with a current limiting starting device which will limit the starting current to 250 percent of the full load current. This will permit the average normal current, normal torque NEMA Design “B” squirrel cage motor of 10 horsepower or less to be started with a magnetic full-voltage starter. Most squirrel cage induction motors, 10 to 75 HP, inclusive, may be started with an auto transformer type starter connected to give a starting voltage of 80% of full voltage.
Induction motors larger than 75-HP shall be of the wound rotor type and shall be started with an increment type starter which will limit the starting current to 15% of the full load running current.
All 3 phase motors shall be protected by approved devices which will protect the motor from overload, single-phasing, under- and over- voltage, and ground faults.
All motor installations, both single-phase and 3-phase, shall comply with Article 430 of the latest version of the NEC ®.