Basic Principles Of Planning - Siemens SIMATIC S7-300 Hardware And Installation Manual

Configuring
5.2

Basic Principles of Planning

Important information about planning
Warning
Open equipment
The modules that make up an S7-300 are regarded as open equipment. This
means that you must always install the S7-300 in a cubicle, cabinet or electrical
control room that can only be accessed using a key or tool. Only trained or
authorized personnel are allowed access to such cubicles, cabinets or electrical
operating rooms.
Caution
Depending on the field of application, operation of an S7-300 in a plant or system
is defined by special rules and regulations . Note the safety and accident
prevention regulations relating to specific applications, e.g. machine protection
directives. This Chapter and the Appendix General rules and regulations on S7-
300 operation provides an overview of the most important rules you need to
consider when integrating an S7-300 into plant or system.
CPU and expansion module (EM)
An S7-300 PLC consists of a central unit (CU) and – if required – one or multiple
expansion modules (EMs).
The rack containing the CPU is referred to as the central unit (CU). Racks
equipped with modules form the expansion modules (EMs) connected to the
system's CU.
When should I use expansion modules?
You can use EMs if the number of CU slots is insufficient for your application.
When using EMs, you might require further power supply modules in addition to the
extra racks and interface modules (IM). When using interface modules you must
ensure compatibility of the partner stations.
Racks
The rack for your S7-300 is a rail. You can use this rail to mount all modules of
your S7-300 system.
5-2
S7-300 Programmable Controller Hardware and Installation
A5E00105492-02