Electrical Cabinet Design; Correct Installation Of Fans - Siemens SINUMERIK 808D ADVANCED Commissioning Manual

3.4

Electrical cabinet design

It may be preferable to always use cooling units as this allows the cabinet to be sealed which is the best option for stopping
the entry of contaminants. Within the cabinets it may also be necessary to install fans to ensure the air is circulated and
prevent "hot spots" from forming.
The technical specifications of the individual hardware component will provide details of the power loss measured in Watts.
Calculations are made to see if the cabinet can dissipate the heat naturally.
The cabinet manufacturer can supply details of the heat-loss of the cabinet.
Natural heat dissipation occurs through the cabinet walls providing the wall is in free air and not against a wall for example.
A general rule is that the energy dissipated is approximately 50 Watts/m² of free cabinet wall assuming a 10 °C temperature
difference between the cabinet and the outside air.
3.4.1

Correct installation of fans

For cabinets it is possible that the cooling can be achieved with fans drawing air from the outside via a filter. Natural
convection causes the warm air to exit via a filter.
The fact that air is being drawn directly from the outside means that this system can never be airtight. Having a fan for the
inlet side only ensures that the cabinet is positively pressurized which helps keep contaminants from entering.
It is extremely important that the filters are service regularly to avoid ingress of contaminants and to maintain the efficiency
of the cooling process.
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Commissioning Manual
01/2017