SUBJECT: PROPER
WIRING PRACTICES FOR AC and DC DRIVES
The subject
of electrical noise (Radio Frequency Interference and Electro-Magnetic
Interference) is a hot topic. Electrical noise can cause erratic performance,
and even failures, of AC and DC Drives. It often occurs because customers
do not pay attention to proper wiring techniques when installing AC
and DC Drives.
When investigating
possible noise problems, please check that the following guidelines
have been followed during the installation and wiring of AC and DC Drives.
These guidelines are just as important inside the customer's cabinet
as they are in wiring on the machine.
1.
Power leads must be separated from signal leads. High voltage leads
such as incoming line, or outgoing armature and field circuits can be
run together, but must be separated from low voltage signals. In addition,
stranded copper wire should be used, not a solid conductor.
2.
If a noise filter is installed in advance of the AC or DC Drive, the
wiring from the filter to the drive should be as short as possible.
It is also necessary to shield the motor leads once a noise filter is
installed.
3.
Low voltage leads such as potentiometers, inhibit and enable circuits,
start/stop and reversing commands can be further divided into two groups,
switching and analog signals. These leads can be run together as long
as the analog signals (potentiometer or voltage following) are shielded
from the switching signals (inhibit, start/stop or reversing). Signal
leads, such as potentiometers, transducers or milliamp signals, should
be wired with either shielded or twisted wire. Multi conductor twisted
cable is recommended. If shielded wire must be used, the shield must
be securely grounded at the AC and DC Drive end only. However, there
may be times when grounding the shield is not necessary. This may only
be determined by trial and error.
4.
When low voltage and/or high voltage leads must go to the same location,
for example, to an in-cabinet terminal strip, or through conduit to
the machine, they must be wired separately. It is not acceptable to
use a cable or "drop cord" which mixes these leads together.
If these leads cross in a cabinet, they should do so at right angles
to minimize the influence of induced magnetic fields.
