External Wiring Precautions - Mitsubishi Electric MELSEC-F FX3G Series User Manual

FX Series Programmable Controllers
3G
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.
Reverse voltage 5 to 10 times of the load voltage
Forward current Load current or more
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.
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
PLC output
limit
element
20 Terminal Block
11
12
13
14
Forward
15
Reverse
16
17
18
19
20
375