Omron SYSMAC C20K Installation Manual page 28

Wiring CPUs and Expansion I/O Units Section 2–5
tance must be less than 100 Ω. Do not use a ground–wire longer than 20 m.
Care must be taken because ground resistance is affected by the nature of
the ground, water content, season, and the amount of time that has elapsed
since the wire was laid underground.
CPU operation may be adversely affected if the ground–wire is shared with
other equipment, or if grounding is attempted by attaching the ground–wire to
the metal superstructure of a building. When either Expansion I/O Units or
I/O Link Units are used, they also require grounding at the GR terminal.
These may all be included on the same ground.
GR
LG
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