Datasheet

QT20.241, QT20.241-C1
Q-Series
24V, 20A, THREE PHASE INPUT
Oct. 2006 / Rev. 1.0 DS-QT20.241-EN
All parameters are specified at 24V, 20A, 3x400Vac, 25°C ambient and after a 5 minutes run-in time unless otherwise noted.
www.pulspower.com Phone [phone] Germany
19/23
27.5. OUTPUT CIRCUIT BREAKERS
Standard miniature circuit breakers (MCBs) can be used for branch protection. Ensure that the MCB is rated for DC
voltage, too. The following tests show which circuit breakers the power supply 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 power supplies. 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 power supply end of the cable (loop impedance approx. 20mOhm)
Fig. 27-5 Branch protectors, test circuit 1
Circuit
Breaker
Power
Supply
AC
DC
+
-
I
Load
+
-
S1
Parameters:
Input voltage:3x 400Vac, load current: 0A
Tripping time shorter than 5s.
The following circuit breaker tripped during the test:
A- or Z- Characteristic:: equal or smaller 25A
B- Characteristic: equal or smaller 16A
C- Characteristic: equal or smaller 10A
Test 2: Short circuit with S1 on the load end (additional impedance included; represents longer load wire length).
Fig. 27-6 Branch protectors, test circuit 2
R
Circuit
Breaker
Power
Supply
AC
DC
+
-
I
S1 Load
+
-
Parameters:
Input voltage: 3x 400Vac, load current: 0A
Tripping time shorter than 5s.
The following circuit breaker tripped during the test:
A- or Z- Characteristic:: ≤ 16A and R< 82mOhm
B- Characteristic: ≤ 6A and R< 180mOhm
C- Characteristic: ≤ 8A and R<= 150mOhm
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
82mOhm
2.3m 3.2m 4.6m 6.9m 11.4m 18.3m
150mOhm
4.2m 5.9m 8.4m 12.5m 20.9m 33.4m
180mOhm
5.0m 7.0m 10.0m 15.0m 25.1m 40.1m
Example:
Which wire gauge must be used to trip a B-Characteristic circuit breaker with a rating of 6A? The load wire length is
21m.
Answer: A 6A B-Characteristic circuit breaker requires a loop impedance of less than 180mOhm (test results). The wire
length table shows that up to 25.1m wire with a cross section of 2.5mm
2
are below 180mOhm. A wire not smaller
than 2.5mm
2
shall be used.