Vfd cable terminations / braiding, shielding, etc

[lefty51]

Currently doing a small industrial job, installing cabling for ( 20 ) 5 hp motors. There seems to be a wide opinion of how the vfd cables should be terminated....braiding, shielding, etc Any advice would be appreciated ,or any links as well. Thx.

 

[DickDV]

What country are you in. What is the supply voltage. What is the motor nameplate data. How far is the motor in wire distance from the drive. Are you intending to run the motor leads in conduit or in an open cable tray?

All of these are important to getting you the right answer.

 

[lefty51]

Voltage is 480v / 3 phase. Distance from mcc room to motor control panel is approx. 200', and then another 80 max. to each motor. Cabling is tray style cable ( no armour ), and # 12 / 3c. I believe its belden 29502. Its run in open tray, not conduit. Engineering spec'd out the cable, but we do not have any specs as to terminations.

 

[DickDV]

The three power leads are to be connected to the drive output terminals and to the motor leads as usual. The shield and the ground conductor are to be connected together at the drive end and tied to the drive cabinet ground. The shield and the ground conductor are to be tied to the motor frame ground terminal at the motor end. The same motor ground terminal must be connected to ground.

The shield and the ground lead form a ground bond between the drive and motor ground forcing them to the same potential. This is important to avoid nuisance faulting on the drive.

 

[LionelHutz]

You're also supposed to use a gland or cable connector which connects and grounds the shield around the full diameter of the cable. Only using the drain or ground wire or connecting to the shield at one point degrades the shielding.

 

[lefty51]

Yes, once the guys stripped the larger feed cable which feeds the starter panel, this cable had a spiral copper wrap. This would be very difficult to install under a ground lug somehow, so a proper cable connector with a grounding gland would be definitely more suitable. Also, just for your info, there are 2 additional bare leads in the cable ( drain wires, additional grounds ( not green though ) and these 2 leads seem to be directly in contact with the copper wrap. Thx guys!