Rockwell Automation 7000A PowerFlex Medium Voltage AC Drive - Air-Cooled (A Frame) - Manual (Page 69)

Drive Installation 2-39
7000 “A” Frame 7000A-RM001A-EN-P – January 2011
• Protection from Radiated and Conducted Noise
Reasonable care should be taken when connecting and routing power
and signal wiring on a machine or system. Radiated noise from nearby
relays, solenoids, transformers, non linear loads (such as motor drives)
etc. can couple onto signal wires producing undesired pulses. In fact
the encoder itself may induce noise into signal lines run adjacent to it.
To avoid radiated and/or conducted noise, power and signal lines
should be run separately with a minimum distance between them of
at least 75 mm (3 inches). If they have to overlap somewhere in the
system, then the power lines should be run at 90° to the signal lines.
Signal lines should also use twisted pair shielded cable and run in
separate conduit that should be grounded to the building ground.
Encoder wires and shields should maintain continuity throughout,
from the encoder to the drive. Avoid the use of a terminal block in a
junction box. This has the potential of creating radiated noise and
ground loops.
The encoder case must be grounded to the building ground to insure
proper and reliable operation. Most encoders have provision for a
case ground connection through the connector/cable pair if a ground
connection cannot be made through the mounting bracket/machine
ground. DO NOT ground the encoder case through both the
machine and cable wiring. Use low capacitance wires (≤ 40 pf/ft)
with 100% shield coverage for long cable runs and connect the shield
only at the drive end.
Wrong Shield
Connection
Encoder
Drive
Figure 2.26 – Encoder Shield Ground
For more protection against electrical noise, specify an encoder with
complementary outputs and connect with twisted pair cable. With
this type of cabling, the induced currents will self-cancel.
As a final precaution, ground the shield together with all other parts
of the system that require grounding to a single point ground. This
will reduce varying ground potentials caused by high current fluxes
created by motors, remote control switches and magnetic fields.