Siemens CPU 313C Hardware And Installation Manual page 37

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You should install your S7-300 in a cabinet when any of the following apply:
• If you plan a larger system
• You are using your S7-300s in an environment subject to interference or
contamination
• In order to meet UL/CSA requirements, which require installation in cabinets
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Take the following criteria into account:
• Ambient conditions at the cabinet's place of installation
• The specified mounting clearance for racks (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.
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Further information on degree of protection can be found in IEC 529 and
DIN 40050.
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The power dissipation capability of a cabinet depends on its type, ambient
temperature and on the internal arrangement of devices.
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Siemens catalogs NV21 and ET1 contain more detailed information about power
dissipation.
S7-300 Automation System, Hardware and Installation: CPU 31xC and CPU 31x
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