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Busbar Systems
General data
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Siemens LV 10 · 2014
10
Current-carrying capacity values for flat bars acc. to DIN 43671
According to DIN 43671, current-carrying capacity values for flat
bars are defined as 35 °C ambient temperature and 65 °C bus-
bar temperature.
If a higher bar temperature than 65 °C is possible, the busbars
can be operated with higher current values according to the
following formula:
I
=
I
n
*
k
2
Example
Under normal operating conditions (35 °C ambient temperature
and 65 °C bar temperature), a 30 x10 mm busbar can handle
loads up to 630 A. However, you want the busbar to handle a
higher current, at the expense of an increased busbar tempera-
ture of max. 85 °C.
The following applies:
• Bar type: Busbar
• Busbar size: 30 x 10
• Max. bar temperature: 85 °C
• Ambient temperature: 35 °C
The figure on the right shows the correction factor
k
2
= 1.3 for the
current-carrying capacity.
This results in a higher value of 630 A * 1.3 = 819 A.
If the 30 x10 busbar is to be operated with a bar temperature of
85 °C, it may be loaded with maximum 819 A.
Current-carrying capacity values for 30 x 10 mm flat bars acc. to
DIN 43671, depending on ambient and bar temperature
2,2
0
5
10
I201_18479
15
20
25
30
35
40
45
50
55
60
65
2,1
2,0
1,9
1,8
1,7
1,6
1,5
1,4
1,3
1,2
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
50 55 60 65 70 75 80 85 90 95 100 105 110115120 125
Factor k
2
Air temperature °C
Busbar temperature °C
© Siemens AG 2014