Rockwell Automation 7000A PowerFlex Medium Voltage AC Drive (A Frame) - ForGe Control - Manual (Page 49)

Rockwell Automation Publication 7000A-UM200C-EN-P - June 2014 49
Drive Installation Chapter 2
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 4V 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.