Additional Installation Tips
7.6 Galvanic Isolation
The operator panel has galvanic isolation against the 24 V DC power supply but no
galvanic isolation between the communication ports for RS-232, RS-422, RS-485,
CAN and USB. Only the Ethernet connection has galvanic isolation.
*
*
*
*
*
*
*
*
*
Operator panel
Modular controller
Printer
PC
PC
Different ground potential
*
= Internal 0 V (GND) connection
Power CPU
COM COM2
RS422
RS232
USB
When a PC is connected to the operator panel, the internal 0 V (GND) of the
panel is connected to the protective ground via the PC.
A number of USB devices can have the shield connected together with the
protective ground. Here, the 0 V (GND) of the operator panel is connected to the
protective ground when, for example, a USB memory stick, keyboard, or similar
device is plugged in.
If a number of units are connected that have a 0 V and a ground connection, and
these are connected to various grounding points, there is a substantial risk of
problems. Grounding currents go through communication cables, the rear plate
of the controller, internally in the operator panel, and can cause errors.
Beijer Electronics, MAEN228
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