Rockwell Automation 7000A PowerFlex Medium Voltage Drive (A-Frame) - Classic Control - Manual (Page 93)

Drive Installation 2-53
7000 “A” Frame 7000A-UM150F-EN-P – June 2013
Note that if a drive isolation transformer is used, the WYE secondary
neutral point should not be grounded.
Each AC motor frame must be bonded to grounded building steel
within 6 m (20 feet) of its location and tied to the drive's ground
bus via ground wires within the power cables and/or conduit. The
conduit or cable armor should be bonded to ground at both ends.
Grounding Guidelines and Practices for Drive Signal and Safety
Grounds
When interface cables carrying signals where the frequency does not
exceed 1 MHz are attached for communications with the drive, the
following general guidelines should be followed:
• It is good practice for the mesh of a screen to be grounded
around its whole circumference, rather than forming a pigtail that
is grounded at one point.
• Coaxial cables with a single conductor surrounded by a mesh
screen should have the screen grounded at both ends.
• Where a multi-layer screened cable is used (that is, a cable with
both a mesh screen and a metal sheath or some form of foil), there
are two alternative methods:
– The mesh screen may be grounded at both ends to the metal
sheath. The metal sheath or foil (known as the drain) should,
unless otherwise specified, be grounded at one end only,
again, as specified above, at the receiver end or the end which
is physically closest to the main equipment ground bus.
or
– The metal sheath or foil may be left insulated from ground
and the other conductors and the mesh cable screen
grounded at one end only as stated above
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.