VSD cable

[powersoff]

What should you do with the VSD cable shield wire at a motor disconnect?
My intent was to join earth ground and shield at motor and VSD. But I am not sure what to do with shield at disconnect.

Thanks

 

[jpolson]

The siemens, weg, and AB drives that I have installed all had the shield grounded at both ends.

I hate to say it, but what does the wiring diagram in the manual show?


Joel Olson

 

[Marke]

Hello Powersoff

It is important that you connect the screen at both ends if you wish to minimize the noise generated by the VFD.

The screen should be clamped all the way around the cable using a metal cable clamp, or an EMC gland at each end.

Do not use pigtails for the connection of the screen as this greatly reduces the effect of the screen.

The major reason for using the screen, is to provide a very low impedance path for the high frequency noise current coupled into the motor frame to return to the VFD frame.
Pigtails effectively reduce the surface area and thereby increase the HF impedance, reducing the effectiveness of the return path.

If you have a disconnect switch between the VFD and the motor, it is equally important that you continue the low impedance path through. One way is to clamp the screens to a common metal plate where the cables enter and exit from the isolator. Once again, do not connect the screen by using pigtails.

Best regards,
Mark.

Mark Empson
L M Photonics Ltd

 

[powersoff]

Diagram shows power earth and shield joined at motor and vfd.
Disconnect is not shown.
We are using a nonmetallic disconnect with terminal blocks.
2 possible choices are keep earth and shield isolated at disconnect or jumper together at terminal block in disconnect.

 

[Marke]

At the disconnect, the earth wires can be joined in a connector block.
The screens must not be joined in a connector block as that requires a pigtail to be made.
Either clamp the screens together by exposing the screens on the cable and overlapping the cables and using a metal jubilee clamp (hose clip) or a metal plate with the two cables clamped to the plate by clamping around the screens.
The screen must be continuous right through from the VFD to the motor and the surface area of the screen must not be reduced at any point.

Best regards,
Mark

Mark Empson
L M Photonics Ltd