Installing And Removing The S7-200 Modules - Siemens Simatic S7-200 System Manual

Power Budget
All S7-200 CPUs have an internal power supply that provides power for the CPU, the expansion modules,
and other 24 VDC user power requirements.
The S7-200 CPU provides the 5 VDC logic power needed for any expansion in your system. Pay careful
attention to your system configuration to ensure that your CPU can supply the 5V power required by your
selected expansion modules. If your configuration requires more power than the CPU can supply, you
must remove a module or select a CPU with more power capability. Refer to Appendix A for information
about the 5 VDC logic budget supplied by your S7-200 CPU and the 5 VDC power requirements of the
expansion modules. Use Appendix B as a guide for determining how much power (or current) the CPU
can provide for your configuration.
All S7-200 CPUs also provide a 24 VDC sensor supply that can supply 24 VDC for input points, for relay
coil power on the expansion modules, or for other requirements. If your power requirements exceed the
budget of the sensor supply, then you must add an external 24 VDC power supply to your system. Refer
to Appendix A for the 24 VDC sensor supply power budget for your particular S7-200 CPU.
If you require an external 24 VDC power supply, ensure that the power supply is not connected in parallel
with the sensor supply of the S7-200 CPU. For improved electrical noise protection, it is recommended
that the commons (M) of the different power supplies be connected.
Warning
Connecting an external 24 VDC power supply in parallel with the S7-200 24 VDC sensor supply can
result in a conflict between the two supplies as each seeks to establish its own preferred output voltage
level.
The result of this conflict can be shortened lifetime or immediate failure of one or both power supplies,
with consequent unpredictable operation of the PLC system. Unpredictable operation could result in
death or serious injury to personnel, and/or damage to equipment.
The S7-200 DC sensor supply and any external power supply should provide power to different points.

Installing and Removing the S7-200 Modules

The S7-200 can be easily installed on a standard DIN rail or on a panel.
Prerequisites
Before you install or remove 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.
Warning
Attempts to install or remove S7-200 or related equipment with the 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 S7-200 CPUs or related equipment.
Always ensure that whenever you replace or install an S7-200 device you use the correct module or
equivalent device.
Warning
If you install an incorrect module, the program in the S7-200 could function unpredictably.
Failure to replace an S7-200 device with the same model, orientation, or order could result in death or
serious injury to personnel, and/or damage to equipment.
Replace an S7-200 device with the same model, and be sure to orient and position it correctly.
Installing the S7-200 Chapter 3
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