Panasonic FP0R User Manual page 81

Installation and Wiring
1 PLC
2 Other device (inverter etc.)
Risk of short circuits
Depending on the surroundings in which the equipment is used, grounding may cause
problems.
Example 1:
Since the power supply line of the FP0/FP0R expansion unit (24V DC and 0V terminal) is
connected to the function earth through a varistor, the varistor may be shorted if there is an
irregular potential between the power supply line and function earth. (The power supply line of
the FP0R is connected to function earth through a high-voltage capacitor. Therefore, there is
no risk of a short-circuit.)
24V DC
0V
PE
Power supply line of FP0R with built-in 39V varistor
Example 2:
Do not ground the function earth terminal of the FP0R when grounding a plus terminal (+) of
the power supply.
In some computers, the SG terminal of the RS232C port is connected with the connector
shielding. Also, the FP0R TOOL port shielding is connected with the function earth terminal
(PE). Therefore, the GND and function earth terminals of the FP0R may be connected if a
computer is connected. Especially when the FP0R is connected to a computer with a plus
terminal (+) grounded, the minus terminal (-) of an FP0R is connected with the function earth
terminal. A resulting short circuit may damage the FP0R and its neighboring parts.
A
24V
GND
0V
PE
80
OK
B
2
SG
1
A
B
C
C
SG
1
Power supply 1 Shielding
CPU 2 Cable
Computer