Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - Classic Control - Manual (Page 77)

2-42 Drive Installation
7000-UM150I-EN-P – June 2013 7000 “B” Frame
Grounding Practices (cont.) Grounding Requirements and Grounding Specification for
Customers and Power Integrators
An external ground must be attached to the main ground bus. The
grounding means must comply with applicable local codes and
standards. As general guidelines, for information only, the ground
path must be of sufficiently low impedance and capacity that:
• the rise in potential of the drive ground point when subjected to a
current of twice the rating of the supply should be no higher than
4 volts over ground potential.
• the current flowing into a ground fault will be of sufficient
magnitude to cause the protection to operate.
The main grounding conductor(s) should be run separately from
power and signal wiring so that faults:
• do not damage the grounding circuit,
or
• will not cause undue interference with or damage to protection or
metering systems, or cause undue disturbance on power lines.
Identification of Types of Electrical Supplies – Grounded and
Ungrounded Systems
When dealing with an ungrounded, three-phase electrical supply
system, the cable insulation must be capable of handling not only the
phase to phase voltage, but also the voltage to ground if one of the
other phases develops a ground fault. In practice, the cable
insulation of an ungrounded, three-phase system must be good for at
least a continuous voltage of root three (1.732) times the rated
voltage of the supply.
Ground Bus
The drive ground bus runs along the top of the drive at the front.
The ground bus is accessible at the top of each of the drive
enclosures when the enclosure door is opened (and the low voltage
compartment hinged out in the case of the incomer cabinet). It is the
responsibility of the installer to ensure that the drive is grounded
properly, typically at the point on the ground bus in the incomer
cabinet, close to the incoming power terminations.