355 / 408
11
11/41
Dimensions
Section 12
Circuit breakers for direct
current applications (cont.)
24 V - 48 V direct current applications
Technical advice
Tripping curves
We can choose our solution according to the inrush currents generated by our
loads, in the same way as for alternating current. In direct current, the same thermal
tripping curves are obtained as in alternating current. The only difference is that the
magnetic thresholds are offset by a coefficient
√
2 compared to the curves obtained
in alternating current.
Characteristics of the various curves and their applications:
Curves Magnetic thresholds DC applications
AC
DC
Z
2.4 to 3.6 In 3.4 to 5 In
b
b
Resistive loads
b
b
Loads with electronic circuits
B
3.2 to 4.8 In 4.5 to 6.8 In b
b
Motor inductor: starting current 2 to 4 In
b
b
Battery charger/Uninterruptible power supply
(UPS)
C
6.4 to 9.6 In 9.05 to 13.6 In b
b
Electronic controller
D et K
9.6 to 14.4 In 13.6 to 20.4 In b
b
Electromagnetic coil: inrush overvoltage
10 to 20 Un
b
b
LV relay
b
b
Trip units (MN, MX)
b
b
Indicator light
b
b
PLCs (industrial programmable
logic controllers)
The figures opposite are iC60 tripping curves showing DC magnetic thresholds and
normative limits
Example
Protection of the 4 mm
2
cable supplying a load at In = 30 A with a 32 A rating and a
tripping curve that allows the starting current for this load to be absorbed.
DB124188
t(s)
0,01
0,1
1
10
100
1000
I / In
B C D
1
5.7
±20%
11.3
±20%
17
±20%
3600s for I/In=1.3
3600s
for
I/In=1.05
Curves B, C, D, ratings 6 A to 63 A
DB124244
t(s)
0,01
0,1
1
10
100
1000
I (A)
100
1000
10
4mm
2
cable
fusioncurve
Starting
current
iC60,32A
Ccurve
Curve C, rating 32 A (AC magnetic thresholds in dotted lines)
DB124451
I / In
t(s)
0,01
0,1
1
10
100
1000
K
Z
1
4.2
±20%
17
±20%
3600s for I/In=1.3
3600s
for
I/In=1.05
Curves Z, K, ratings 6 A to 63 A