90 / 582
BETA Protecting
Miniature Circuit Breakers
Configuration
1/68
Siemens ET B1 · 10/2008
1
*
You can order this quantity or a multiple thereof.
Selectivity for miniature circuit breakers/fuses
Distribution systems are usually set up as radial networks.
An overcurrent protection device is required for each reduction of
the conductor cross-section. This produces a series connection
staggered according to rated currents, which should, if possible,
be "selective".
Selectivity means that, in the event of a fault, only the protective
device that is directly next to the fault in the current path is
tripped. This enables current paths in parallel to maintain a
power flow.
In the case of miniature circuit breakers with upstream fuses, the
selectivity limit depends largely on the current limitation and
tripping characteristics of the miniature circuit breaker and the
melting
I
2
t value of the fuse.
This produces different selectivity limits for miniature circuit
breakers with different characteristics and rated switching
capacity.
The following tables provide information on the short-circuit
currents up to which selectivity is still maintained between min-
iature circuit breakers and upstream fuse according to
DIN VDE 0636-21. The values specified in kA are limit values
that were determined under unfavorable test conditions. Under
normal practical
conditions, you can often expect considerably better values,
depending on the upstream fuses.
Limit values of selectivity for miniature circuit breakers/fuses in kA
Downstream miniature circuit breakers
Upstream fuses
I
n
[
A]
16
A
20
A
25
A
35
A
50
A
63
A
80
A
100
A
5
SY6
Characteristic B
6
0.3
0.4
0.7
1.2
3.0
3.2
•
•
10
--
0.4
0.6
1.0
2.2
3.0
5.0
•
13
--
--
0.5
1.0
2.2
3.0
5.0
•
16
--
--
--
1.0
2.0
2.4
4.0
•
20
--
--
--
--
2.0
2.4
4.0
•
25
--
--
--
--
--
2.0
3.5
•
32
--
--
--
--
--
1.7
2.9
•
40
--
--
--
--
--
--
2.0
4.0
50
--
--
--
--
--
--
--
4.0
Characteristic C
2
0.3
0.5
1.2
1.7
•
•
•
•
3
0.3
0.4
0.8
1.4
4.0
5.0
•
•
4
0.3
0.4
0.6
1.1
3.0
4.0
•
•
6
--
0.4
0.6
1.0
2.4
3.2
•
•
8
--
--
0.5
0.9
1.4
2.6
3.1
•
10
--
--
0.5
0.9
1.4
2.1
3.1
•
13
--
--
--
0.8
1.3
2.0
3.0
•
16
--
--
--
0.8
1.3
2.0
3.0
•
20
--
--
--
--
1.3
2.0
2.7
•
25
--
--
--
--
--
2.0
2.4
5.0
32
--
--
--
--
--
--
2.2
4.0
40
--
--
--
--
--
--
--
3.5
50
--
--
--
--
--
--
--
3.0
63
--
--
--
--
--
--
--
3.0
•
r
rated switching capacity 5SY6 according to EN 60898
.
6 000
© Siemens AG 2008