CUE selection
Grundfos CUE
40
Special conditions
Derating must be taken into account when using the
CUE in these situations:
• low air pressure (heights)
• low speeds
• installations with long motor cables
• cables with a large cross-section
• high ambient temperature.
The required action is described in the next sections.
Low air pressure
At low air pressure, the cooling capability of air is
reduced.
At altitudes above 3,280 ft (1,000 m), the max. output
curr
ent should be derated in accordance with the dia-
gram in fig. 49.
Fig. 49 Derating of output current at low air pressure
At altitudes above 6,600 ft (2,000 m), PELV cannot be
met. PELV = Protective Extra Low Voltage.
An alternative is to lower the ambient temperature at
high alti
tudes and thereby ensure 100% output current
at high altitudes.
Example 2
At an altitude of 6,600 ft (2,000 m), the output current
27 A
of the selected CUE in example 1 must be derated
to 92% according to fig. 49. This is equal to 25 A.
High ambient temperature
If the output current is reduced to 80 % of the nominal
output current of the CUE in questions, the ambient
may be 5 °C higher.
The other possibility is to use a unit one size bigger. For
high
er temperature increases, bigger units are
required. The efficiency of the CUE will, however, be
reduced at higher temperatures.
If the CUE gets too hot, it will reduce the switching
frequency.
Note that the nominal temperature rating depends on
th
e enclosure type.
The maximum ambient temperature of the different
enclo
sures can be found in section
Technical data on
p. 45.
TM04 0222 5107
3,280 ft (1km)
6,600 ft (2 km)
9,800 ft (3 km)
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