Functions
and characteristics
Selection guide for DC circuit
breakers
Solutions depending on the distribution system
and the voltage
Parallel connection of poles
Type of distribution system
2
2
DB116988
Isolated
Isolated polarities
DB116987
Mid-point connected to earth
DB116986
Protected polarities
Diagrams
(and types of faults)
Earthed
One polarity (negative here) connected to earth
(or exposed conductive parts)
1 (disconnection of 1P)
2 (disconnection of 2P)
DB116985
Type
Source
Selection of circuit breaker and pole connection
Compact NS
Two, three-pole, 2, 3P in
Four-pole, 2 x 2P in parallel.
parallel, four-pole, 4P in parallel.
Four-pole, 2 x 2P in parallel.
DB115861
DB115861
DB115861
DB115860
Un y 250 V
Four-pole, 2 x 2P in parallel.
DB115861
DB115862
250 V < Un y 500 V
Four-pole, 2 x 2P in parallel,
connected in series.
Breaking capacity of parallel solutions
Two-pole
Three-pole
Four-pole
2 poles in parallel
3 poles in parallel
4 poles in parallel
2 x 2 poles in parallel, connected in series
Four-pole, 2 x 2P in parallel.
Un y 250 V
N
85
-
250 V < Un y 500 V
H
100
-
DC
100
100
100
N
-
H
-
DC
100
Comparison of series and parallel connection in terms of performance
Series connection of poles divides the
voltage per pole and optimises breaking
capacity for high-voltage systems.
Series connection of poles on a DC circuit breaker is the means to:
b divide the system voltage by the number of poles
b use the rated current for each pole
b use the breaking capacity of the circuit breaker for all the poles.
For example, a Compact NS630, 3P DC type, with the three poles connected in
series, provides:
b a maximum voltage of 750 V (250 V per pole)
b a rated current of 630 A
b a breaking capacity of 100 kA / 750 V.
Consequently, a 630 A / 250 V device can be used in a 750 V system.
Parallel connection of poles divides the
current per pole and optimises the rated
current for systems that do not exceed the
withstand voltage of each pole.
The maximum useable rating and the value
of the magnetic setting are indicated (see
page B-8) and (see page B-9).
Parallel connection of poles, on the contrary, imposes the system voltage on each
pole, but is the means to:
b divide the current flowing through each pole by the number of poles
b increase the rated current.
For example, the same Compact NS630 DC 3P circuit breaker with three poles in
parallel provides:
b a maximum voltage of 250 V (250 V per pole)
b a rated current of 1500 A (see table page B-9)
b a breaking capacity of 100 kA / 250 V.
Consequently, a 630 A device used in a 250 V system can handle 1500 A.
A-4