Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C Frame) - Classic Control - Manual (Page 119)

Drive Installation 2-83
7000 “C” Frame 7000L-UM300I-EN-P – June 2013
Each power feeder from the substation transformer to the drive must
be provided with properly sized ground cables. Utilizing the conduit
or cable armor as a ground is not adequate.
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.
Refer to Note 3 in Table 2.A for recommendations on shield
grounding.
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