Cables and Fuse Sizes For Motor Circuit

Cables and Fuse Sizes For Motor Circuit Points : Cables and Fuse Sizes For Motor Circuit, Examples of calculation about cables and fuse sizes for motors Always, choose the correct size of cable for motor circuit. When we choose a cable for motor circuit, keep in mind that the current carrying capacity of motor and its terminal voltage drop. For example, if the voltage drop occurs in a motor circuit is 10% of terminal voltage4 it means the loss of power or torque (T x v²) is 20%. Always keep in mind these points, when we deal with 50H.P three phase motors and 20H1P single phase or D.C motors.

(1) Always use the 7/0.029 or large than cable size in motor circuits.
(2) If the distance between distribution fuse board and motor is greater than 100 ft, then always calculate the volt-drop in cable.
(3) Keep in mind, these factors when we choose the size of cable, temperature, insulation of cable and starting current of motor.
(4) For suitable motor circuits, the size of sub-circuit fuses is depend upon the type of fuse (Re wire able or HIR.C) and type of motor starter.
(5) The rating of sub-circuit fuse is not greater than the twice of the cable rating. Examples of Calculation About Cables and Fuse Sizes for Motors The method in which we determined the correct size of cable is as following.
(1) Find the full load current (see motor name plate or table or use calculation method).
(2) Type of motor eg. three-phase squirrel cage induction motor.
(3) Method of motor starting (D.O.L or star-delta).
(4) Type of fuses. (Re-wire able or H.R.C).
(5) Multiply the full load current of motor with sub-circuit fuse ratings.
(6)To determine the cable current rating, divide the fuse current rating by 2. e.g. cable current ratings = Sizes of circuit breakers 15, 20, 25, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200A Sizes of H.RC fuses 2, 4, 6, 10, 15, 20, 25, 30, 35, 40, 50, 60, 80, 100, 125, 160, 200, 250, 300A