Woodward Vertex-Pro, Installation/Hardware Manual

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Manual 26489V1 Vertex-Pro Motor-Driven Compressor Control
Woodward 27
Grounding and Shielding
The RS-422 and RS-485 specifications state that a ground wire is needed if there
is no other ground path between units. The preferred method to do this is to
include a separate wire in the cable that connects the circuit grounds together.
Connect the shield to earth ground at one point only. The alternate way is to
connect all circuit grounds to the shield, and then connect the shield to earth
ground at one point only. If the latter method is used, and there are non-isolated
nodes on the party line, connect the shield to ground at a non-isolated node, not
an isolated node. Figures 5-7 and 5-8 illustrate these cabling approaches.
Non-isolated nodes may not have a signal ground available. If a
signal ground is not available, use the alternate wiring scheme in
Figure 7-24 with the signal ground connection removed on those
nodes only.
Figure 5-7—Preferred Multipoint Wiring Using Shielded Twisted-Pair Cable with
a Separate Signal Ground Wire
The SG (signal ground) connection is not required if signal ground is
unavailable.
Figure 5-8—Alternate Multipoint Wiring Using Shielded Twisted-Pair Cable
without a Separate Signal Ground Wire