Simple tips for select cable size for a motor:
When you want to
select a cable for motor, you need to calculate 125% to 150% load current of
motor rating current. It is necessary for the high starting ampere of motor. If
you select cable as rating of motor, it should be burn within some time. So,
for safety, you should select a cable over the ampere rating of the motor.
For example, for a 3 phase 30 Kw motor has running on 400 V
with Power factor 0.8 and efficiency is 80%
Here, P = 30 kw = 30 ×
1000 = 30000 W
V = 400 v
Power factor, Cos θ
= 0.8
Efficiency, η
= 80% = 0.8
From the power law,
P = √3ηVICos θ
30000 =
1.73 × 0.8 × 400 × I × 0.8 [√3
= 1.73…]
I =
30000 / 442.88
I =
67.74
So, you
need to select,
67.74 × 1.25 = 84. 675 Ampere Capacity Cable
Or,
67.74 ×
1.5 = 101.61 Ampere Capacity Cable
Now,
you can easily select cable for your motor.
