Siemens COMBIMASTER Reference Manual page 67

Continuous Current Ratings.
As explained above, the continuous rating
depends on the amount of cooling available for
the inverter from the motor fan. This can be
affected by one or more of the following:
Size of Motor Fan Cover Cutout
There must be a hole cut in the motor fan
cover to allow air from the motor fan to be
directed onto the inverter heatsink. The size
and shape of this hole affects the airflow to the
inverter.
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COMBIMASTER & MICROMASTER Integrated
Position of the Inverter
Ideally, the inverter should be positioned so
that the hole in the motor fan cover is centered
directly beneath the inverter heatsink. In
addition, the vertical distance from the fan
cover to the inverter heatsink should be as
small as possible.
Motor Speed
When the motor fan is driven by the motor
shaft, then a slower motor will have less air
flow to the inverter.
Mains Voltage
When the 380 to 500V inverters are operated
on a high mains voltage, there is normally
more heat generated in the inverter. This will
result in a lower continuous current rating. This
is not normally a problem, because a motor
operated at the higher voltage will require less
current to deliver the same shaft power.
Siemens plc. 1999
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REFERENCE MANUAL