Galvanic Isolation - Beijer Electronics BoX2 pro Installation Manual

6.6. Galvanic Isolation

The HMI 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
RS422 RS232
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PC
*
When a PC is connected to the HMI 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 HMI 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 HMI panel, and can cause
errors.
Use external units to improve communication and achieve galvanic isolation. Westermo has good
industry-standard insulators that are also insulated from the 24 V DC feed.
Beijer Electronics, MAEN275
Modular controller
USB
*
*
Different ground potential
*
= Internal 0 V (GND) connection
21
Additional Installation Tips
Printer
Power CPU COM COM2
* * *
PC
*
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2023-09