Rockwell Automation 1398-DDM-xxx ULTRA 100 Series Drives Installation Manual - Manual (Page 278)

Publication 1398-5.2 – PDF 1997
E-5 Electromagnetic Compatibility Guidelines for Machine Design
When multiple power cables enter an enclosure, an unfiltered line can
contaminate a filtered line external to the enclosure. Therefore, all
lines must be filtered to be effective. The situation is similar to a leaky
boat. All the holes must be plugged to prevent sinking.
If the filter is mounted excessively far from the drive, it may be
necessary to mount it to a grounded conductive surface, such as the
enclosure, to establish a high frequency (HF) connection to that
surface. To achieve the HF ground, direct contact between the
mounting surface and the filter must be achieved. This may require
removal of paint or other insulating material from the cabinet or panel.
The only reasonable filtering at the drive output terminals is the use of
inductance. Capacitors would slow the output switching and
deteriorate the drive performance. A common mode choke can be
used to reduce the HF voltage at the drive output. This will reduce
emission coupling through the drive back to the AC line. However, the
motor cable still carries a large HF voltage and current. Therefore, it is
very important to segregate the motor cable from the AC power cable.
More information on cable shielding and segregation is contained in
the section on shielding.
Grounding
High frequency (HF) grounding is different from safety grounding. A
long wire is sufficient for a safety ground, but is completely
ineffective as an HF ground due to the wire inductance. As a rule of
thumb, a wire has an inductance of 8 nH/in regardless of diameter. At
low frequencies it acts as a constant impedance, at intermediate
frequencies as an inductor, and at high frequencies as an antenna. The
use of ground straps is a better alternative to wires. However the
length to width ratio must be 5:1, or better yet 3:1, to remain a good
high frequency connection.
The ground system’s primary purpose is to function as a return current
path. It is commonly thought of as an equipotential circuit reference
point, but different locations in a ground system may be at different
potentials. This is due to the return current flowing through the ground
systems finite impedance. In a sense, ground systems are the sewer
systems of electronics and as such are sometimes neglected.
!
Intro
ATTENTION: Large leakage currents exist in AC line
filters. They must be grounded properly before applying
power. Filter capacitors retain high voltages after power
removal. Before handling the equipment, voltages should
be measured to determine safe levels prior to handling the
equipment. Failure to observe this precaution could result
in severe bodily injury.