Configuring
4.9 Electrical assembly, protective measures and grounding
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05
4-15
Result
The figure below shows the resultant ambient temperatures, based on an accumulated
power loss of 650 W:
Table 4-6 Cabinet selection
Cabinet design Maximum permitted ambient
temperature
Closed with natural convection and forced convection (trend
3)
Operation not possible
Open with through-ventilation (trend 2) approx. 38 °C
Closed with heat exchanger (trend 1) approx. 45 °C
Cabinet types suitable for horizontal installation of the S7-300:
• open, with closed ventilation
• closed, with heat exchanger
4.9 Electrical assembly, protective measures and grounding
4.9.1 Grounding concept and overall structure
This section contains information about the overall configuration of an S7-300 connected to a
grounded TN-S network:
• Circuit-breaking devices, short-circuit and overload protection to VDE 0100 and VDE
0113
• Load power supplies and load circuits
• Grounding concept
Note
An S7-300 can be used in many different ways, so we can only describe the basic rules
for the electrical installation in this document. Those basic rules are a must in order to
achieve a fully functional S7-300 system.
Definition: Grounded mains
In a grounded mains network, the neutral conductor is always bonded to ground. A short-
circuit to ground of a live conductor, or of a grounded part of the system, trips the protective
devices.
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