Siemens Simatic S7-300, Hardware And Installation Manual, Page: 42 / 242

Configuring
S7-300 Programmable Controller Hardware and Installation
4-14
A5E00105492-01
Result:
The table below shows the ambient air temperatures at a total power loss of 650
W, as a result of the figure above:
Table 4-6 Cabinet selection
Cabinet design Maximum permissible ambient
temperature
Closed, with natural convection and forced convection
(curve 3) Operation not possible
Open, with enclosed ventilation (curve 2) approx. 38 °C
Closed, with heat exchanger (curve 1) approx. 45 °C
For a vertical installation of the S7-300 you can choose between the following
cabinet types:
•
open, with closed ventilation
•
closed, with heat exchanger
4.8 Electrical assembly, protective measures and grounding
4.8.1 Grounding conception and overall structure
Introduction
Below you can find information on the overall structure of an S7-300 operated on a
grounded power supply (TN-S network). The following aspects are covered:
•
Circuit-breaking devices, short-circuit and overload protection to VDE 0100 and
VDE 0113
•
Load power supplies and load circuits
•
Grounding conception
In view of the many and versatile S7-300 applications, this chapter can only
describe the basic rules on its electrical configuration. You must observe at least
these basic rules if you want your S7-300 to operate free of trouble.
Definition: Grounded power supply (PEN)
The neutral is grounded in a grounded power supply system (PEN). A single short-
circuit to ground between a live conductor or a grounded part of the system trips
the protective devices.
Components and protective measures
A number of components and protective measures are prescribed for plant
installations. The type of components and the degree of compulsion pertaining to
the protective measures will depend on the VDE specification applicable to your
particular plant.