Rockwell Automation 1606-XLE960MX-3N Power Supply Reference Manual - Manual (Page 18)

All parameters are specified at 48V, 20A, 3x480Vac, 25°C ambient and after a 5 minutes run-in time, unless noted otherwise.
18 Rockwell Automation Publication 1606-RM025A-EN-P — April 2014
Bulletin 1606 Switched Mode Power Supplies
25.3. Output Circuit Breakers
Standard miniature circuit breakers (MCBs or UL 1077 supplementary breakers) can be used for branch protection
but make sure that the MCB is rated for DC voltage as well. The following tests show which circuit breakers the power
supply will typically trip.
Circuit breakers have huge tolerances in their tripping behavior. These typical tests can therefore be used only 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. 25-2 Branch protectors, test circuit 1
Circuit
Breaker Power
Supply
AC
DC
+
-
I
Load
+
-
S1
Parameters:
Input voltage:
3x400Vac, load current: 0A
The following circuit breaker tripped during the test:
A
- or Z - Characteristic: equal or smaller 25A *)
B - Characteristic: equal or smaller 32A *)
C - Characteristic: equal or smaller 20A *)
Test 2: Short circuit with S1 on the load end (additional impedance included; represents longer load wire length).
Fig. 25-3 Branch protectors, test circuit 2
R
Circuit
Breaker Power
Supply
AC
DC
+
-
I
S1 Load
+
-
Parameters:
Input voltage:
3x400Vac, load current: 0A
The following circuit breaker tripped during the test:
A
- or Z - Characteristic: ≤ 25A and R= 50mOhm *)
B - Characteristic: ≤ 32A and R= 29mOhm *)
C - Characteristic: ≤ 20A and R= 82mOhm *)
What does this resistance mean in wire length?
1.0mm 2 1.5mm 2 2.5mm 2 4.0mm 2 6.0mm 2 10mm 2
29mOhm 1.6m 2.4m 4.0m 6.5m 9.7m 16.2m
50mOhm 2.8m 4.2m 7.0m 11.1m 16.7m 27.9m
82mOhm 4.6m 6.9m 11.4m 18.3m 27.4m 45.7m
*) A list of the circuit breakers under testing is avaliable upon request.
Example:
Which wire gauge must be used at a length of 8.5m before a B-Characteristic circuit breaker with 32A trips?
Answer: A 32A B-Characteristic circuit breaker requires a loop impedance of less than 29mOhm based on the test
results. The wire length table shows that a length of 9.7m with a cross section of 6.0mm
2 has an impedance of
29mOhm. A wire no smaller than 6.0mm 2 must be used.