Additional Installation Tips
7.6 GalvanicIsolation
The operator panel has galvanic isolation against the 24VDC 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 Printe
PCPC
Different ground potential
* = Internal 0 V (GND) connection
Power CPU COM COM2
RS422 RS232 USB
When a PC is connected to t
he operator panel, the internal 0 V (GND) of the
panel is connected to th
eprotectivegroundviathePC.
A number o f USB d evices 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 connect
ed to various grounding points, there is a substantial risk of
problems. Groun
ding currents go through communication cables, the rear plate
of the controlle
r, internally in the operator 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.
BeijerElectronics, MAEN249B
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