Siemens Simatic S7-300, Hardware And Installation Manual, Page: 39 / 242

Configuring
S7-300 Programmable Controller Hardware and Installation
A5E00105492-01
4-11
4.6 Selection and installation of cabinets
Necessity of cabinets
You can install the S7-300 in a cabinet for operation in larger plants or if ambient
interference or contamination is to be expected.
For compliance with UL/CSA standard it is required, amongst other things, to install
components in cabinets.
Selecting and dimensioning of cabinets
Note the following criteria when selecting and dimensioning cabinets:
•
Ambient conditions at the cabinet's place of installation
•
The specified mounting clearance for module racks (profile rails)
•
Total power loss of all components in the cabinet
The ambient conditions (temperature, humidity, dust, chemical influence, explosion
hazard) at the cabinet's place of installation determine the degree of protection (IP
xx) required for the cabinet. Further information on degree of protection is found in
IEC 529 and DIN 40050.
Important cabinet types
The table below gives you an overview of the commonly used cabinet types. It
shows you the applied principle of heat dissipation, the calculated maximum power
loss and the degree of protection.
Table 4-5 Cabinet types
Open cabinets Closed cabinets
Enclosed
ventilation via
natural convection Increased
enclosed
ventilation Natural convection Forced convection
with rack fan,
improvement of
natural convection Forced convection
with heat
exchanger, internal
and external
auxiliary ventilation