Guidelines For Grounding And Wiring - Siemens SIMATIC S7-200 System Manual

S7-200 Programmable Controller System Manual

Guidelines for Grounding and Wiring

Proper grounding and wiring of all electrical equipment is important to help ensure the optimum
operation of your system and to provide additional electrical noise protection for your application
and the S7-200.
Prerequisites
Before you ground or install wiring to any electrical device, ensure that the power to that
equipment has been turned off. Also, ensure that the power to any related equipment has been
turned off.
Ensure that you follow all applicable electrical codes when wiring the S7-200 and related
equipment. Install and operate all equipment according to all applicable national and local
standards. Contact your local authorities to determine which codes and standards apply to your
specific case.
Warning
Attempts to install or wire the S7-200 or related equipment with power applied could cause
electric shock or faulty operation of equipment. Failure to disable all power to the S7-200 and
related equipment during installation or removal procedures could result in death or serious
injury to personnel, and/or damage to equipment.
Always follow appropriate safety precautions and ensure that power to the S7-200 is disabled
before attempting to install or remove the S7-200 or related equipment.
Always take safety into consideration as you design the grounding and wiring of your S7-200
system. Electronic control devices, such as the S7-200, can fail and can cause unexpected
operation of the equipment that is being controlled or monitored. For this reason, you should
implement safeguards that are independent of the S7-200 to protect against possible personal
injury or equipment damage.
Warning
Control devices can fail in an unsafe condition, resulting in unexpected operation of controlled
equipment. Such unexpected operations could result in death or serious injury to personnel,
and/or damage to equipment.
Use an emergency stop function, electromechanical overrides, or other redundant safeguards
that are independent of the S7-200.
Guidelines for Isolation
S7-200 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 S7-200 product data
sheets as having 1500VAC or greater isolation. This designation is based on a routine factory test
of ( 2Ue + 1000VAC ) or equivalent according to approved methods. S7-200 safe separation
boundaries have been type tested to 4242 VDC.
The sensor supply output, communications circuits, and internal logic circuits of an S7-200 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 S7-200 is connected to ground. Other S7-200 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 S7-200 low voltage circuits, external connections to
communications ports, analog circuits, and all 24V 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.
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