User manual

CD5.241, CD5.241-S1
CD–Series
DC/DC Converter; 24V, 5A
Jan. 08 / Rev. 1.1 DS-CD5.241-EN / All parameters are specified at 24V, 5A and 24Vdc input at 25°C ambient unless otherwise noted.
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27.4. OUTPUT CIRCUIT BREAKERS
Standard miniature circuit breakers (MCBs or UL1077 circuit breakers) can be used for branch circuit protection.
Ensure that the MCB is also rated for DC voltage. The following tests show which circuit breakers the DC/DC converter
typically trips.
Circuit breakers have huge tolerances in their tripping behavior, therefore, these typical tests can only be used as a
recommendation or for comparing two different DC/DC converters. Furthermore, the loop impedance has a major
influence on whether a breaker trips or not. Two tests were performed, representing typical situations:
Test 1: Short circuit with S1 on the DC/DC converter end of the cable (loop impedance approx. 20mOhm)
Fig. 27-3 Branch protectors, test circuit 1
Circuit
Breaker
DC/DC
Converter
Input
DC
+
-
I
Load
+
-
S1
Parameters:
Input voltage: 24Vdc, load current: 0A
The following circuit breaker tripped during the test:
A- or Z- Characteristic:: equal or smaller 8A *)
B- Characteristic: no tripping ≥ 6A *)
no breaker available < 6A
C- Characteristic: equal or smaller 3A *)
Test 2: Short circuit with S1 on the load end (additional impedance included; represents longer load wire length).
Fig. 27-4 Branch protectors, test circuit 2
R
Circuit
Breaker
DC/DC
Converter
AC
DC
+
-
I
S1 Load
+
-
Parameters:
Input voltage: 24Vdc, load current: 0A
The following circuit breaker tripped during the test:
A- or Z- Characteristic:: ≤ 6A and R= 180mOhm *)
B- Characteristic: no tripping ≥ 6A *)
no breaker available < 6A
C- Characteristic: ≤ 3A and R= 270mOhm *)
What does this resistance mean in wire length?
0.5mm
2
0.7mm
2
1.0mm
2
1.5mm
2
2.5mm
2
4.0mm
2
180mOhm
5.0m 7.0m 10m 15m 25m 40m
270mOhm
7.5m 10.5m 15m 23m 38m 60m
*) A list of the circuit breakers under test is available on request.
Example:
Which wire gauge must be used to trip a C-Characteristic circuit breaker with a rating of 3A? The load wire length is
21m.
Answer: A 3A C-Characteristic circuit breaker requires a loop impedance of less than 270mOhm (test results). The wire
length table shows that up to 23m wire with a cross section of 1.5mm
2
are below 270mOhm. A wire not smaller than
1.5mm
2
shall be used.