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Motor Earthing IEC

Motor Earthing IEC

Motor Earthing IEC

(OP)
In IEC, do we need to run 4-core cables (3 phases plus earth) from MCC to each motor, or can we run three core cables (3 phases) from MCC to motors and earth the motors locally from the main earthing loop?   

RE: Motor Earthing IEC

timm333,
It depends on the earthing practice in your industry.
1)If you have an earthing system covering the plant with sevaral rods(a grid),then the motor body can be bonded to the grid locally,without running a seperate earthing conductor from the MCC.This TNS(IEC60364)system will ensure a low zero sequence impedance (higher earth fault currents)during an earth fault.
2)If the motor is located very remotely and far away from the grid,and you are unable to bond to the grid,then you should run a seperate earthing conductor from the MCC to the motor so that you have a TNS(IEC60364)system again.

In any case,since the local earthing connection at the motor body is always considered as the "SAFETY EARTH" and NOT the "SYSTEM EARTH",I always use a seperate earthing conductor from the MCC to the load(s)in addition to the local earthing at the motor.
 

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