ABB S800 I/O User Manual page 97

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To avoid overheating, when ambient temperatures are high, the heat dissipated in
the electronics cabinet must be taken into consideration. This is particularly the case
with sealed cabinets (IP54) or tropicalized cabinets (IP41).
The frequency of faults is estimated to be doubled for each 20°C increase in
temperature. It is therefore important to maintain a low temperature where the
equipment is installed.
The different hardware modules in the controller and the I/O system have different
outputs of heat. Accurate calculation of the heat produced by the system requires
knowledge of the modules and the work cycle.
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The maximum permitted temperature below the I/O station in the cabinet is 55 °C.
The permissible amount of heat generated depends on the type of cabinet and its
location.
In critical applications with an I/O station fully equipped and cabinets arranged in
groups, it may be necessary to make a calculation of the actual power dissipation
and an estimation of the temperature rise within the cabinet. It is recommended that
you re-calculate when you expand the system as well.
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When calculating the heat generated in a cabinet, the heat generated by the different
I/O modules must be summed, and then added to the heat generated by the power
supply units and other equipment such as an extra modem, extra unit for supply of
power to transmitters etc.
Section 3.1.8, Power and Cooling
modules in the S800 I/O system.
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gives the power dissipated as heat by hardware
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