Pepperl+Fuchs PS1000-A6-24.20, Technical Information

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Power Supply PS1000-A6-24.20
Application Notes
26.2 Output Circuit Breakers
Standard miniature circuit breakers (MCB's or UL 1077 circuit breakers) are commonly used
for AC-supply systems and may also be used on 24V 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 24V 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.
Figure 26.4 Test circuit
Maximal wire length
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for a fast (magnetic) tripping:
0.75mm² 1.0mm² 1.5mm² 2.5mm²
C-2A 31m 37m 63m 98m
C-3A 28m 34m 51m 78m
C-4A 18m 25m 38m 58m
C-6A 9m 11m 18m 26m
C-8A 6m 7m 12m 14m
C-10A 4m 6m 11m 13m
C-13A 2m 2m 4m 7m
B-6A 23m 28m 46m 66m
B-10A 11m 14m 19m 32m
B-13A 7m 11m 16m 29m
B-16A 5m 6m 8m 15m
B-20A 1m 1m 2m 4m
B-25A – – – 1m
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Don’t forget to consider twice the distance to the load (or cable length) when calculating the total wire length
(+ and – wire).