Control Enclosures; Special Motor Considerations - Baldor 29M Installation And Operating Manual

Section 1
General Information
Electrical Noise Considerations

Control Enclosures

Special Motor Considerations

5-16 Troubleshooting
Continued
The cure for some electrical noise may be a grounded metallic control enclosure. The
enclosure should be grounded to the building ground with a short, heavy gauge wire.
Also, the power conduit, motor lead conduit and signal wire conduit must be grounded to
the enclosure. Sometimes paint and seals prevent electrical contact between conduit
and the cabinet. Sometimes wire or straps are used to ensure good electrical grounding.
Motor frames are also on the required grounding list. As with control enclosures,
motors should be grounded directly to plant ground with as short a ground wire as
possible. Here's why. Capacitive coupling within the motor windings produces transient
voltages between the motor frame and ground. The severity of these voltages increases
with the length of the ground wire. Installations with the motor and control mounted on a
common frame, and with heavy ground wires less than 10 ft. long, rarely have a problem
caused by these motor–generated transient voltages.
Another cure may be needed when the motor frame transient voltages are capacitively
coupled to feedback devices mounted on the motor shaft. Especially with optical
encoders, these transients create noise on the signal leads and disrupt drive operation.
To prevent this problem, add electrical isolation between the motor and the feedback
device to stop the current flow and the resulting transients. The most simple isolation
method, shown in Figure 5-10, has two parts: 1) A plate of electrical insulating material
placed between the motor mounting surface and the feedback device. 2) An insulating
coupling between motor shaft and the shaft of the feedback device.
Figure 5-10 Isolated Mounting Method
Insulating plate
Resolver or other
feedback device
Insulating Coupling
Mounting bracket
MN1230