Output circuit breakers

Standard circuit breakers (or UL1077 circuit breakers) are generally used for AC supply systems and can also be used for DC branches.

Circuit breakers are used to protect cables and circuits. If the ampere value and the characteristics of the circuit breaker are matched to the cable thickness used, the wiring is considered thermally safe, regardless of whether the circuit breaker opens or not.

To avoid voltage drops and situations with undervoltage in adjacent 24 V branches fed from the same source, a fast (magnetic) trip of the circuit breaker is desirable. Fast switch-off within 10 ms is required, which approximately corresponds to the bridging time of PLCs. This requires power supplies with high reserve current and large output capacitors. In addition, the impedance of the faulty branch must be sufficiently small for the current to actually flow. The following table contains typical test results that show which circuit breakers with B and C characteristics trip magnetically, depending on the wire cross-section and the wire length.

Output circuit breakers 1:
Test circuit

Maximum wire length*) for fast (magnetic) tripping:

 

0.75 mm2

1.0 mm2

1.5 mm2

2.5 mm2

C-2A

29 m

39 m

56 m

86 m

C-3A

26 m

34 m

49 m

76 m

C-4A

16 m

21 m

29 m

46 m

C-6A

3 m

5 m

7 m

8 m

C-8A

1 m

2 m

2 m

3 m

C-10A

1 m

1 m

1 m

1 m

 

0.75 mm2

1.0 mm2

1.5 mm2

2.5 mm2

B-6A

18 m

23 m

31 m

54 m

B-10A

4 m

6 m

7 m

13 m

B-13A

3 m

5 m

6 m

11 m

B-16A

1 m

1 m

1 m

2 m

*) Don't forget to double the distance to the load (or the cable length) when calculating the total cable length (plus and minus cable).