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

3.3.3

Motor heating conditions

The rated motor specifications are continuous allowable values at a surrounding air temperature of 40 °C when the motor is
installed with a steel flange. When the motor is mounted on a small surface, the motor temperature may rise considerably
because of the limited heat radiating abilities of the surface. Make sure you use a suitable flange according to Siemens
recommended flange sizes.
Note
The actual temperature rise depends on how the flange (motor mounting section) is fixed on the installation surface, what
material is used for the motor mounting section, and motor speed. Always check the actual motor temperature.
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.
Commissioning Manual
6FC5397-4EP10-0BA8, 07/2018
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