Application notes
PS2001-2410-0000
30
Version: 1.0
To avoid voltage drops and situations with undervoltage in adjacent 24V branches fed from the same source,
a fast (magnetic) trip of the circuit breaker is desirable. Fast switch-off within 10ms is required, which
approximately corresponds to the bridging time of PLC. 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.
Fig. 21: Test circuit
Maximum wire length
*)
for fast (magnetic) tripping:
0.75mm
2
1.0mm
2
1.5mm
2
2.5mm
2
C-2A
30m
37m
54m
84m
C-3A
25m
30m
46m
69m
C-4A
9 m
15 m
25m
34m
C-6A
3 m
3 m
4 m
7 m
C-8A
0.75mm
2
1.0mm
2
1.5mm
2
2.5mm
2
B-6A
12 m
15 m
21m
34m
B-10A
3 m
3 m
4 m
9 m
B-13A
2 m
2 m
3 m
6 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).
4.5
Series connection
Power supplies of the same type can be connected in series to increase the output voltages. As many
devices can be connected in series as necessary, as long as the sum of the output voltages does not exceed
150Vdc. Voltages with a potential higher than 60Vdc are no longer regarded as safety extra-low voltage and
can be dangerous. Such voltages must be protected with a touch guard.
Grounding of the output is required if the sum of the output voltage is more than 60Vdc.
Avoid application of return voltage (e.g. from a braking motor or battery) to the output terminals.
Restrictions: Keep a mounting distance of 15mm (left/right) between two power supplies and do not install
the power supplies above each other. Power supplies connected in series should only be used in the
standard installation position (terminals on the underside of the device).
Remember that leakage current, electromagnetic interference, inrush current and harmonics increase when
using multiple power supplies.
