Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 166)

0
20
40
60
80
100
120
0 0.2 0.4 0.6 0.8 1
Distance [m ]
T
em
p
er
at
u
re [
°C
]
Fig. 6.1-1
Typical decrease in conductor temperature with increasing distance from the terminal
Decisive for the functional reliability of devices, their life span or the risk of accidents, is not the
temperature-rise but the absolute temperature. The standards define temperature-rise limits for
practical reasons so that tests can be performed in a laboratory environment. The reference
ambient temperature in accordance with standards is 35 °C as an average over 24 hours with a
maximum value of 40 °C. If the ambient temperature around the devices exceeds these values
in actual service – for example because they are installed in a switching cabinet – then their
load must be reduced correspondingly so that the permissible absolute temperature values are
observed. This especially affects the temperatures of internal parts of devices in respect of the
thermal stability of the materials used. For reduction factors, see manufacturers documentation.
Temperatu
re °C
0
20
40
60
-20
Fig. 6.1-2
The normal temperature range for devices in accordance with IEC 60947 is identical with the normal
temperature range for switchgear assemblies in accordance with IEC 60439, in which the devices are
installed.
6.1.2 Laboratory test conditions and real practical environment
The temperature-rise test of low-voltage devices and hence the determination of their permissi-
ble thermal loads is performed in accordance with standards under precisely defined conditions.
This is important to obtain comparable measurement results.
The test conditions are:
ƒ Set-up of device to be tested in open air
ƒ Measurement of the ambient temperature at 1 m horizontal distance
ƒ Connections to the current source and between the terminals with defined conductor cross
sections (depending on the rated current)
ƒ Connections to the current source and between the terminals with a minimum length of 1 m
up to cross section 35 mm
2
, at bigger cross sections 2 m and over 800 A rated current 3 m.
35 °C 24 h average
40 °C
maximum value
LVSAM-WP001A-EN-P - April 2009 6-2