External Wiring Precautions - Mitsubishi FX3U SERIES User Manual

FX Series Programmable Controllers
3U
User's Manual - Hardware Edition

20.8.4 External wiring precautions

1. Protection circuit for load short-circuits
A short-circuit at a load connected to an output terminal
could cause burnout at the output element or the PCB. To
prevent this, a protection fuse should be inserted at the
output. Use a load power supply capacity that is at least 2
times larger than the total rated fuse capacity.
2. Transistor protection circuit for inductive loads
The transistor output circuit in the terminal block is
equipped with a Zener diode (50V) for protection. When
an inductive load is connected, however, a diode should
be connected parallel to the load when required. The
diode must comply with the specifications shown below.
Counter voltage
Forward current
3. Interlock
For loads such as forward/reverse contactors, etc., where
a hazardous condition could result if switched ON
simultaneously, an external interlock should be provided
for interlocking the PLC's internal programs as shown to
the right.
426
5 to 10 times of the load voltage
Load current or more
20 FX-16/32E*-*-TB (Terminal Block)
20.8 FX-16EYT-TB, FX-16EYT-H-TB
Load
0 to 7
Fuse
COMn
Terminal block
inductive
load
0 to 7
Fuse
COMn
Terminal block
Forward
limit Interlock
Reverse
limit
PLC output
element