● Configure safety circuits external to the programmable controller to ensure that the entire system
operates safely even when a fault occurs in the external power supply or the programmable
controller. Failure to do so may result in an accident due to an incorrect output or malfunction.
(1) Emergency stop circuits, protection circuits, and protective interlock circuits for conflicting
operations (such as forward/reverse rotations or upper/lower limit positioning) must be
configured external to the programmable controller.
(2) When the programmable controller detects an abnormal condition, it stops the operation and all
outputs are:
• Turned off if the overcurrent or overvoltage protection of the power supply module is
activated.
• Held or turned off according to the parameter setting if the self-diagnostic function of the
CPU module detects an error such as a watchdog timer error.
Also, all outputs may be turned on if an error occurs in a part, such as an I/O control part, where
the CPU module cannot detect any error. To ensure safety operation in such a case, provide a
safety mechanism or a fail-safe circuit external to the programmable controller. For a fail-safe
circuit example, refer to "General Safety Requirements" in the MELSEC-L CPU Module User's
Manual (Hardware Design, Maintenance and Inspection).
(3) Outputs may remain on or off due to a failure of a component such as a relay and transistor in an
output circuit. Configure an external circuit for monitoring output signals that could cause a
serious accident.
● In an output circuit, when a load current exceeding the rated current or an overcurrent caused by a
load short-circuit flows for a long time, it may cause smoke and fire. To prevent this, configure an
external safety circuit, such as a fuse.
● Configure a circuit so that the programmable controller is turned on first and then the external power
supply. If the external power supply is turned on first, an accident may occur due to an incorrect