Siemens SIMATIC ET 200SP HA Manuel D'utilisation page 50

If you want to configure the IO device with grounded reference potential, then connect the 1M connection of the interface
module to the protective conductor galvanically.
In Ex applications, the following applies:
• The product must also be supplied with limited power (Limited Power Source, LPS) in accordance with IEC 60950-1 or IEC
62368-1
or
• The power supply unit of the product complies with NEC Class 2 in accordance with the National Electrical Code (r) (ANSI /
NFPA 70).
The product has reverse polarity protection.
3.15.2 Connection to low voltage
Certain I/O modules are suitable for connection to the low-voltage supply system (TT, TN, IT) (see Intended use (Page 36)).
The connections of the line conductors are marked on the product as follows:
L,N
Grounded infeed
When a plant is in operation, the current flows over the neutral conductor. In the event of a fault, such as a single ground
fault between a live conductor and ground, the current flows over the protective conductor. In the description of grounded
infeeds (TN-S system), the neutral conductor (N) and the protective conductor (PE) are each grounded. Both conductors form
part of the overvoltage concept.
IO device with ungrounded reference potential on low voltage
This configuration discharges high-frequency interference currents and prevents static charges.
To discharge interference currents, the reference potential of the interface module and the light-gray and black terminal
blocks is connected to the mounting rail (protective conductor) internally via an RC combination. (The following applies in
this case: IM: R = 10 MΩ / C = 100 nF, light-gray / black terminal block: R = 10 MΩ / C = 4 nF).
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ET 200SP HA Distributed I/O System
A5E52222765-AB, 11/2024