3 replies to this topic

[AB2005]

Dear Friends,

It is a common practice for us to connect one end of shield wire of power cable of servo motor with motor body and other end to the chases of drive. But I found an application where the shield was connected just only the chases of drive, for motor end, it was floating. I checked the drawing of machine and found here the same configuration. This confused me as it is against the normal practice.
Can any body has answer about it?

[marke]

Hello AB2005

The screen should be connected at both ends, but there are serious misunderstandings out there where some "experts" claim that you should only earth one end of the screen.

For control signals and low level analog signals, you only earth one end where you are likely to create an earth loop by connecting both ends. The earth loop can result in moderate currents (relative to the control signal) that can cause interference.
For power circuits on the output of VFDs or Servo Drives where the output voltage is PWM, it is imperative that you connect both ends of the screen using 360 degree clamp type connections.
This provides a low impedance high frequency earth return path for the currents capacitively coupled to the frame of the motor.

see http://www.vfd-emc.co.nz for more explanations.

Oops, another earth quake rattled through. felt like a good 5.

Best regards,
Mark.

[marke]

Hello AB2005

Is this resolved??

Best regards,
Mark.

[AB2005]

Hi Marke,

Sorry for late reply, was busy in a project.
I have asked that question to the machine supplier but their is a deep silent yet. I am waiting and if they would not reply, i will connect the shield at motor end also.