Installation
3.4 Wiring guidelines
S7-200 SMART
50 System Manual, 09/2015, A5E03822230-AC
The 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. Isolation boundaries which meet these requirements have been identified in
the product data sheets as having 1500 V AC or greater isolation. This designation is based
on a routine factory test of (2Ue + 1000 V AC) or equivalent according to approved methods.
Safe separation boundaries have been type tested to 4242 V DC.
The sensor supply output, communications circuits, and internal logic circuits of the CPU
with included AC power supply are sourced as SELV (safety extra-low voltage) according to
EN 61131-2. These circuits become PELV (protective extra-low voltage) if the sensor supply
M, or any other non-isolated M connection to the CPU is connected to ground. Other M
connections which may ground reference the low voltage are designated as not isolated to
logic on specific product data sheets. Examples are RS485 communications port M, analog
I/O M, and relay coil power M.
To maintain the SELV / PELV character of the low voltage circuits, external connections to
communications ports, analog circuits, and all 24 V 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.
Safe use of power converters
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 result in death or serious injury to personnel, and/or
damage to equipment.
Use only high-voltage-to-low-voltage power converters that are approved as sources of
touch-safe, limited-voltage circuits.
The best way to ground your application is to ensure that all the common and ground
connections of your PLC 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, remember to consider safety grounding requirements and the proper
operation of protective interrupting devices.
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