Site Considerations for Equipment Installation, Grounding, and Wiring Manual
D301452X012
October 2019
28 Wiring Techniques
connections to a twisted shielded pair (with overall vinyl covering) to every end device. To make
start-ups easier, do not use common returns.
Figure 5-1. Field-wired Circuit without a Common Return
Figure 5-2. Field-wired Circuit with a Common Return
Note
Without a common return, there are no sneak circuits and testing is easy.
5.2.2 Use Twisted Shielded Pair Wiring (with Overall Insulation)
For all field I/O wiring, we recommend using twisted shielded pairs with overall insulation. This type
of cable provides discrete insulation for each of the wires and an additional overall insulated
covering that provides greater E.M.I. immunity and protection to the shield as well.
5.2.3 Ground Cable Shields
Do not connect the cable shield to more than one ground point; it should only be grounded at one
end. Cable shields that are grounded at more than one point or at both ends have a tendency to
induce circulating currents or sneak circuits that raise havoc with I/O signals. This occurs when the
ground systems associated with multipoint connections to a cable shield have a high resistance or
impedance between them and a ground induced voltage is developed (due to man-made error or
natural phenomena).
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