Mitsubishi MELSEC-A Series User Manual page 14

(6) Please wire IN/OUT of the connector for the cable correctly.
Please do loopback test, the set confirmation test, and the bureau order
confirmation test after wiring. It might be generated that a baton abnormal passing
cannot be generated when miswiring and the downed bureau which cannot do the
loopback of an arbitrary bureau do the row again even by the reclosing of the power
supply.
(7) Completely turn off the externally supplied power used in the system when
connecting or disconnecting the cable.