Siemens SIMATIC S7-1200 - Page 77

Installation
4.4 Wiring guidelines
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
77
Guidelines for isolation
S7-1200 AC power supply boundaries and I/O boundaries to AC circuits have been designed
and approved to provide safe separation between AC line voltages and low voltage circuits.
These boundaries include double or reinforced insulation, or basic plus supplementary
insulation, according to various standards. Components which cross these boundaries such
as optical couplers, capacitors, transformers, and relays have been approved as providing
safe separation. Only circuits rated for AC line voltage include safety isolation to other
circuits. Isolation boundaries between 24 V DC circuits are functional only, and you should
not depend on these boundaries for safety.
The sensor supply output, communications circuits, and internal logic circuits of an S7-1200
with included AC power supply are sourced as SELV (safety extra-low voltage) according to
EN 61131-2.
To maintain the safe character of the S7-1200 low voltage circuits, external connections to
communications ports, analog circuits, and all 24 V DC nominal power supply and I/O
circuits must be powered from approved sources that meet the requirements of SELV,
PELV, Class 2, Limited Voltage, or Limited Power according to various standards.
WARNING
Use of non-isolated or single insulation supplies to supply low voltage circuits from an AC
line can result in hazardous voltages appearing on circuits that are expected to be touch
safe, such as communications circuits and low voltage sensor wiring.
Such unexpected high voltages could cause electric shock resulting in death, severe
personal injury and/or property damage.
Only use high voltage to low voltage power converters that are approved as sources of
touch safe, limited voltage circuits.
Guidelines for grounding the S7-1200
The best way to ground your application is to ensure that all the common and ground
connections of your S7-1200 and related equipment are grounded to a single point. This
single point should be connected directly to the earth ground for your system.
All ground wires should be as short as possible and should use a large wire size, such as 2
mm
2
(14 AWG).
When locating grounds, consider safety-grounding requirements and the proper operation of
protective interrupting devices.