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Table 12- 5
Current derating as a function of the ambient temperature (inlet air temperature at the air inlet of the enclosed
drive) and installation altitude for enclosed drives in a NEMA 12 enclosure
Installation altitude above
mean sea level in m
0 ... 6600 ft (0 ... 2000 m)
... 8250 ft (... 2500 m)
... 9900 ft (... 3000 m)
... 11550 ft (... 3500 m)
... 13200 ft (... 4000 m)
... 14850 ft (... 4500 m)
... 16500 ft (... 5000 m)
Use of an isolation transformer to reduce transient overvoltages to IEC 61800-5-1
This reduces overvoltage category III to overvoltage category II, which lowers the air
insulation capacity requirements. An additional (input) voltage derating is not necessary if the
following basic conditions are met:
● The isolation transformer must be fed from a low-voltage or medium-voltage network; it
must not be supplied directly from a high-voltage network.
● It is permissible to use the isolation transformer to supply one or more enclosed drives.
● The lines between the isolation transformer and the enclosed drive(s) must be installed in
such as way that the possibility of a direct lightning strike is ruled out; in other words,
overhead lines must not be used.
● The following power network configurations are permissible:
– TN power networks with grounded star point (no grounded phase conductor)
– IT power networks (operation with a ground fault must be limited to the shortest time
12.2.1.3
Current derating as a function of the pulse frequency
When the pulse frequency is increased, the derating factor of the output current must be
taken into account. This derating factor must be applied to the currents specified in the
technical specifications for the cabinet units.
Enclosed Drives
Operating Instructions, 12/2018, A5E36652151A
a t an ambient temperature (air intake temperature) of
68 °F
77 °F
(20 °C)
(25 °C)
100%
100%
100%
100%
100%
100%
100%
100%
100%
96.3%
97.5%
92.1%
93.0%
possible)
Current derating factor
86 °F
95 °F
(30 °C)
(35 °C)
100%
100%
100%
96.3%
98.7%
92.5%
94.7%
90.7%
Technical specifications
12.2 General data
104 °F
113 °F
(40 °C)
(45 °C)
93.3%
86.7%
89.8%
122 °F
(50 °C)
80.0%
801
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