External Wiring Precautions - Mitsubishi FX3UC SERIES User Manual

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

8.12.4 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.
242
5 to 10 times of the load voltage
Load current or more
8 Terminal Block Specifications and External Wiring
8.12 FX-16EYT-ESS-TB/UL
Load
Fuse
inductive
load
Fuse
Forward
Interlock
limit
Reverse
limit
0 to 7
COMn
Terminal block
0 to 7
COMn
Terminal block
PLC output
element