Mitsubishi Electric MELSEC-Q Series User Manual page 88

(g) The cabling of 200m (656.2ft.) or longer distance may produce
leakage current depending on the capacity between lines and
result in an accident.
(h) As a countermeasure against the power surge due to lightning,
separate the AC wiring and DC wiring and connect a surge
absorber for lightning as shown in (i) of item (1).
Failure to do so increases the risk of I/O device failure due to
lightning.
(3) Grounding
(a) Carry out the independent grounding if possible. (Grounding
resistance 100 or less.)
(b) If the independent grounding is impossible, carry out the
shared grounding (2) as shown below.
Other
Programmable
device
controller
Class 3
grounding
(1) Independent grounding.....Best
(c) Use thick cables up to 2mm
to the programmable controller as much as possible so that
the ground cable can be shortened.
(d) If a malfunction occurs due to earthling, separate either LG or
FG of the base module, the device combination, or all the
connection from the earthling.
Other
Programmable
device
controller
Class 3
grounding
(2) Shared grounding.....Good
54
Programmable
controller
(3) Common grounding.....Not allowed
2
. Bring the grounding point close
Other
device