A motor usually built in a frame smaller than that having a continuous rating of one horsepower, open construction, at 1700 -1800 rpm. Within NEMA frame sizes FHP encompasses the 42, 48 and 56 frames. (In some cases the motor rating does exceed 1 HP, but the frame size categorises the motor as a fractional.) The height in inches from the centre of the shaft to the bottom of the base can be calculated by dividing the frame size by 16.