Some applications, however, require more than just matching the starter size to the motor horsepower if successful starting is to be achieved. These include motors that are large relative to the supply system capacity, drive high-inertia loads such as draft fans, start under load, or have non-centrifugal speed-torque characteristics.
This article will review some basic considerations of motor specification and starter selection for these "hard-to-start" applications. We will limit the discussion to AC induction motors as these are the most commonly used.