Grounding of Encoder Cable

70-80 meters is a long run for both the motor and the encoder connections. What do your drive manufacturers recommend?

If you can't get anywhere in that direction, then:

Connect the shield to ground at the drive end only. Continue the shield on each as near as you can to the terminals at both ends. At the drive end, clamp to the chassis with a metallic P-clamp. At the motor end, cover with heatshrink sleeving, with the shield ending as close as possible to the motor terminals.

Hello John

According to manifacturer electrical diagram ,both side of cable grounded.But it is not true as you said.Still time to time encoder signal getting down very short time.it takes about 80 ms and 15-50 rpm at 1500 rpm.I have changed cable as well.Do you know any fiber application on this subject?

Sorry, I don't have any personal experience. Try searching the internet. I found this in about 2 minutes:

http://www.micronor-ag.ch/english/Home_daten/e-mr361.pdf

I do not understand your slang "getting to sour", but it doesn't sound good.

If the signals from your encoder are single ended, I would change to differential. I would also consider adding an optical isolator and an isolated power supply for the encoder. This will guard your equipment from most faults and prevent ground loops which could compromise signal integrity. Differential signal isolators are available from several manufactures. (I've used one from B&B Electronics on an installation with a 600V 2,125hp DC motor with great success.)

Cable Grounding: If your JAMAK signal cable is the type that has individual shields for each twisted pair and an overall shield. I would connect the individual signal pair signals to the encoder common and to the receiving equipment common. I would connect the overall shield to earth ground at both ends. (With grounding shields, there are always exceptions because of unspecified unknowns in the installation.)

For the motor cable shield, bond both ends securely to chassis.