[Design Precautions]
!
WARNING
• Configure safety circuits external to the programming 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).
• Configure a circuit that turns on an external power supply when the main power of
programmable controller is turned on. If the external power supply is turned on first, it could
result in an output error or an operating error.