Size of earthing cable for a drive of 700 A

[maypot]

Hi,

Basically what should be the size of the earthing cable for a drive 700A capacity driving a 400 k W motor @ 400 V 50 Hz.
I am using a 300 mm^2 copper cable on the power sides.
I trust that it should be at least the size of the power cable to sustain the current under fault condition.
Furthermore, the manufacturer of the VSD is requesting an earthing cable between the VSD and the motor.

Bob

 

[EEIre]

You can calculate the min cross sectional area using:

S >= (SQRT(I^2t))/k

S = Cross sectional area of earth cable
I = Fault current
t = disconnection time
k = constant determined from tables related to initial temp of conductor & type of cable

(To BS 7671)