● 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
• 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.
(3) 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 iQ-R Module Configuration
(4) 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
● 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.
● For the operating status of each station after a communication failure, refer to manuals relevant to the
network. Incorrect output or malfunction due to a communication failure may result in an accident.
● When connecting an external device with a CPU module or intelligent function module to modify data
of a running programmable controller, configure an interlock circuit in the program to ensure that the
entire system will always operate safely. For other forms of control (such as program modification,
parameter change, forced output, or operating status change) of a running programmable controller,
read the relevant manuals carefully and ensure that the operation is safe before proceeding. Improper
operation may damage machines or cause accidents.