HEIDENHAIN TNC 410 M Technical Manual page 228

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The following must be considered when positioning the climate control unit:
The position of the climate control unit in the electrical cabinet must be
selected such that under no circumstances is the warm air from the
inverters sucked directly into the climate control unit.
The position of the climate control unit must ensure that the cold air is not
sucked into the inverters before it mixes with the warm air in the electrical
cabinet. This can be ensured with air guide plates.
There must be sufficient room between the climate control unit and the
inverter components for the air in the electrical cabinet to become mixed.
The climate control unit should be positioned lower than the inverters, and
not at the same height as the inverters, and under no circumstances above
them.
Correct placement with resulting airflow when using a climate control unit:
The following must be considered for the settings of the climate control unit:
In order to utilize the maximum power of the inverters, the cold air that flows
into the inverters should not exceed +40 °C. However, the temperature
should also not be too low, otherwise condensation can form on the inverter
components.
If the temperature sensor that regulates the climate control unit is located
within the unit (at the point where the warm air from the electrical cabinet
is sucked in), then the activation temperature of the climate control unit
should be set to +35 °C.
The switching hysteresis must not exceed 5 °C.
HEIDENHAIN Technical Manual for Inverter Systems and Motors