Rockwell Automation 1398-DDM-xxx ULTRA 100 Series Drives Installation Manual - Manual (Page 280)

Publication 1398-5.2 – PDF 1997
E-7 Electromagnetic Compatibility Guidelines for Machine Design
Shielding and Segregation
The EMI radiating from the drive enclosure drops off very quickly
over distance. Mounting the drive in an enclosure, such as an
industrial cabinet, further reduces the radiated emissions. The cabinet
should have a high frequency ground and the size of the openings
should be minimized. In addition, the drive is considered an “open”
device which does not provide the proper IP rating for the
environment in which it is installed. For this reason the enclosure must
provide the necessary degree of protection. An IP rating or Nema
rating (which is similar to IP) specifies the degree of protection that an
enclosure provides.
The primary propagation route for EMI emissions from a drive is
through cabling. The cables conduct the EMI to other devices, and can
also radiate the EMI. For this reason, cable segregation and shielding
are important factors in reducing emissions. Cable shielding can also
increase the level of immunity for a drive. For example:
● Shield termination at both ends is extremely important. The
common misconception that shields should be terminated at only
one end originates from audio applications with frequencies <20
kHz. RF applications must be terminate the shield at both ends,
and possibly at intermediate points for exceptionally long cables.
●
When shielded cables are not terminated at the cable connection
and pass through the wall of a cabinet, the shield must be bonded
to the cabinet wall to prevent noise acquired inside the cabinet
from radiating outside the cabinet, and vice versa.
●
When shielded cables are terminated to connectors, the shield
must be provide complete 360° coverage and terminate through
the connector backshell. The shield must not be grounded inside
the connector through a drain wire. Grounding the shield inside
the connector couples the noise on the shield to the signal
conductors sharing the connector and virtually guarantees failure
to meet European EMC requirements.
●
The shield must be continuous. Each intermediate connector must
continue the shield connection through the backshell.
●
All cables, both power and signal, should use twisted wire pairing.
The shield termination described above provides a coaxial type of
configuration which provides magnetic shielding, and the shield
provides a return path for HF currents that are capacitively coupled
from the motor windings to the frame. If power frequency circulating
currents are an issue, a 250 VAC capacitor should be used at one of the
connections to block 50/60 Hz current while passing HF currents. Use
of a properly shielded motor cable is essential to meet European EMC
requirements.
The following suggestions are recommended for all installations.