7 replies to this topic

[chaterpilar]

Hi !!

I am using armoured cable for VSD ( 100 hp) output to motor.

Is it advisable to ground the armour of the cable on both ends?

chaterpilar

[AB2005]

Hello Chaterpilar

Using an armored cable for VSD out put is not a good practice. Actually armor works as a metallic conduit which protects the cable for any damages. There are special glands used for armored cable which secure the armor from both ends. Therefore, armor grounds from both ends. It is recommended to use a shielded cable instead of armored cable.

If you have already purchased the armored cable then ground the armor from only one end as we ground the shield of shielded cable.

[marke]

Hello caterpilar

When you connect a motor to the output of a VSD, you should always use a screened cable. You need to have a very low impedance on the earth between the motor and the VSD, so it is best to use a cable that has a good screen plus distributed earth conductors as well.

The screen must be connected to the VSD chassis by either a screened gland, or a saddle clamp, and the same at the motor end, where the screen must be connected to the chassis of the motor by either a screened gland or a saddle clamp.

NB the screen must be connected at both ends.
If you refer to the installation instructions that came with the VSD, I am sure that this is what will be described.

The earthing is done this way to minimise the electromagnetic radiation from the VSD and is the only way that you can comply with EMC regulations. - Some drives need additional filters in order to comply with the European regulations.

Best regards,

[AB2005]

Hello Marke

I have read from manuals of VFDs and learned that shield must be ground only from one end. This method is called “drain”.
Check the following link

Grounding BOTH ends of a shielded cable

[marke]

Hello AB2005

While that is true for low voltage signal and control cables, it is definitely not true for the power cables between the output of a VFD and motor.
Please refer to the section in the manuals for VFDs referring to the installation to comply with EMC requirements.
There are many in the industry who believe that the same rules should apply for control cables and power cables. This is not correct.

With control and signal cables, there are isues with earth loops and induced voltages which can be significant relative to the signal voltages. With the cables between the drive and the motor, the screen is used to attenuate the signals from radiating out from the cables. This will only work properly if the drive enclosure - screen - motor housing make one faraday cage. Hence, the termination by screened gland or clamp is very important. If a pigtail is connected to the screen and then connected to the chassis, it is not nearly as effective.

The reduction in electromagnetic radiation can be very significant when a good screen is used and correctly terminated at each end. I have seen levels drop by well over 20dB just by improving the screening and termination.

Best regards,

[marke]

Hello Chaterpilar

Further to my last post, you may find this of interest.

Best regards,

Attached Files

•  VSDs_and_EMC.pdf   109.47KB   58 downloads

[chaterpilar]

Thanks AB and Marke for your valuable opnions...

Since i already have the armoured cable i will use cable gland at both sides to earth it.

Thanks for the file Marke.

Chaterpilar

[AB2005]

There are many in the industry who believe that the same rules should apply for control cables and power cables. This is not correct.

Dear Marke

It is all true what you said. I have also learned from others that shield of shielded cable must connect only from one end but no one guided that this rule is not applicable for power cables. Thanks to you for your kind guide ness.

Hello Chaterpilar

Check the following link form Rockwell Automation. It will also helpful to you for understanding the grounding issues.
Wiring and Grounding Guidelines for PWM AC Drives