Mitsubishi Electric MELSEC-A/QnA Series Handbook page 4

[Design Precautions]
● In an output module, 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 output or
malfunction.
● For the operating status of each station after a communication failure, refer to relevant manuals for
each network.
Failure to do so may result in an accident due to an incorrect output or malfunction.
● When changing data of the running programmable controller from a peripheral connected to the
CPU module or from a personal computer connected to an intelligent function module or special
function module, configure an interlock circuit in the sequence program to ensure that the entire
system will always operate safely.
For program modification and operating status change, read relevant manuals carefully and ensure
the safety before operation.
Especially, when a remote programmable controller is controlled by an external device, immediate
action cannot be taken if a problem occurs in the programmable controller due to a communication
failure.
To prevent this, configure an interlock circuit in the sequence program, and determine corrective
actions to be taken between the external device and CPU module in case of a communication
failure.
● Do not install the control lines or communication cables together with the main circuit lines or power
cables.
Keep a distance of 100mm or more between them.
Failure to do so may result in malfunction due to noise.
● When a device such as a lamp, heater, or solenoid valve is controlled through an output module, a
large current (approximately ten times greater than normal) may flow when the output is turned from
off to on.
Take measures such as replacing the module with one having a sufficient current rating.
● After the CPU module is powered on or is reset, the time taken to enter the RUN status varies
depending on the system configuration, parameter settings, and/or program size. Design circuits so
that the entire system will always operate safely, regardless of the time.
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WARNING
CAUTION