Basic HTML Version
9/13
Circuits supplied with DC current
Choosing a circuit breaker
Miniature circuit
breakers
Dimensions
Section 10
Examples
How to provide protection of a 80 A outgoer on a 125 V DC network whose negative
polarity is earthed: lsc = 15 kA?
The chart opposite informs us that a NC100H (30 kA, 2P, 125 V) circuit-breaker must
be used. The chart on the previous page informs us that both poles must be placed
on the positive polarity. An additional pole can be placed on the negative polarity to
guarantee isolation.
+
-
125 V =
80 A
three-pole
NC100H
How to provide protection of a 100 A outgoer on a 250 V DC network whose
mid-point is earthed: lsc = 15 kA?
Each pole will be subjected to a maximum of U/2 = 125 V. The chart opposite informs
us that a NC100H (30 kA, 2P, 125 V) or NS100N (50 kA, 1P, 125 V) or NS160N (50 kA,
1P, 125 V) circuitbreaker must be used. The chart on page 9/11 informs us that both
poles must contribute to breaking at the voltage 125 V.
+
-
250 V =
100 A
four-pole
NC100H
How to provide protection of a 400 A outgoer on a 250 V DC
unearthed network: lsc = 35 kA?
The chart opposite informs us that a NS400H (85 kA, 1P, 250 V) circuit breaker must
be used. At least 2 poles must contribute to breaking The chart page 9/11 informs us
that the number of poles required for breaking must be distributed over each polarity.
+
-
250 V =
400 A
two-pole
NS400H