Rockwell Automation 1336T Wiring and Grounding Guide, (PWM) AC Drives - Manual (Page 67)

Rockwell Automation Publication DRIVES-IN001M-EN-P - March 2014 67
Best Practices Chapter 4
Loops, Antennas, and Noise
When routing signal or communication wires, do not use routes that produce
loops. Wires that form a loop can form an efficient antenna. Antennas work well
in both receive and transmit modes, and these loops can be responsible for noise
received into the system and noise radiated from the system. Run feed and return
wires together rather than form a loop. Twisting the pair together further reduces
the antenna effects (see
Figure 30 ).
Figure 30 - Avoid Loops in Wiring
Conduit Magnetic steel conduit is preferred. This type of conduit provides the best
magnetic shielding. However, not all applications allow the use of magnetic steel
conduit. Stainless steel or PVC can be required. Conduit other than magnetic
steel does not provide the same level of shielding for magnetic fields induced by
the motor and input power currents.
Install the conduit so it provides a continuous electrical path through the conduit
itself. This path can become important in the containment of high frequency
noise.
Pull the wire gently and carefully through the conduit. Do not nick the wire
insulation when pulling the wires through the conduit. Insulation damage can
occur when nylon coated wiring, such as thermoplastic high heat-resistant
nylon-coated (THHN) or thermoplastic heat and water-resistant nylon-coated
(THWN), is pulled through conduit, particularly 90
° bends. Nicking can
significantly reduce or remove the insulation. Do not use water-based lubricants
with nylon coated wire such as THHN.
Do not route more than three sets of motor cables in one conduit. Maintain the
proper fill rates per the applicable electrical codes.
Do not rely on the conduit as the ground return for a short circuit. Route a
separate ground wire inside the conduit with the motor or input power wires.
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