Datasheet

QS10.301
Q-Series
30V, 8A, SINGLE PHASE INPUT
22.5. OUTPUT CIRCUIT BREAKERS
Standard miniature circuit breakers (MCB’s or UL1077 circuit breakers) are commonly used for AC-supply systems and
may also be used on 30V branches.
MCB’s are designed to protect wires and circuits. If the ampere value and the characteristics of the MCB are adapted to
the wire size that is used, the wiring is considered as thermally safe regardless of whether the MCB opens or not.
To avoid voltage dips and under-voltage situations in adjacent 30V branches which are supplied by the same source, a
fast (magnetic) tripping of the MCB is desired. A quick shutdown within 10ms is necessary corresponding roughly to
the ride-through time of PLC's. This requires power supplies with high current reserves and large output capacitors.
Furthermore, the impedance of the faulty branch must be sufficiently small in order for the current to actually flow.
The best current reserve in the power supply does not help if Ohm’s law does not permit current flow. The following
table has typical test results showing which B- and C-Characteristic MCBs magnetically trip depending on the wire cross
section and wire length.
Fig. 22-5 Test circuit
Maximal wire length
*)
for a fast (magnetic) tripping:
0.75mm² 1.0mm² 1.5mm² 2.5mm²
C-2A
34m 43m 59m 93m
C-3A
27m 31m 53m 81m
C-4A
18m 24m 43m 54m
C-6A
9m 11m 16m 29m
C-8A
5m 7m 10m 15m
C-10A
4m 6m 8m 13m
C-13A
2m 3m 5m 8m
B-6A
14m 20m 29m 44m
B-10A
9m 11m 15m 33m
B-13A
7m 9m 14m 21m
MCB
Power Supply
22/26
AC
DC
+
-
Load
+
-
B-16A
3m 4m 6m 8m
Wire length
S1... Fault simulation switch
S1
*) Don’t forget to consider twice the distance to the load (or cable length) when calculating the total wire length (+ and – wire).
Dec. 2014 / Rev. 2.2 DS-QS10.301-EN
All parameters are specified at 30V, 8A, 230Vac, 25°C ambient and after a 5 minutes run-in time unless otherwise noted.
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