A three phase motor 20hp with a power factor of 0.85 is to be fed by four single-core, PVC insulated,
copper conductor, non-armoured cables, clipped direct on a non-metallic surface in a confined space
with ambient temperature of 45oC at 40 meter run as shown in Figure Q2. Determine the suitable size
of conductor if the voltage drop from the MCB to the motor terminal must less than 2%. (Correction
factor of thermal insulation, Ci = 1 for this installation). Make sure the motor circuit is adequate to
protect against overload current and no undetected small overload by the protective device. If there
a short circuit current of 3000A between phase to phase conductor, determine the maximum
operating time of MCB. Is the motor circuit adequately protected against this short circuit current?
Determine the maximum short circuit current that the motor circuit can withstand


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