EPSITRON® − Electronic Circuit Breakers
Compact and Precise ECBs for DC Circuits
On the secondary side, switched-
mode power supplies provide DC
voltage to control circuit loads
(e.g., controllers, operating panels,
displays and auxiliary relays). These
control circuits also call for wiring
protection and if the load has no
protective unit of its own, device
protection as well. Furthermore, Ma-
chinery Directive EN 60204 requires
the detection of hazardous ground
faults in control circuits and switch-
ing o within ve seconds.
The overcurrent protection in prima-
ry switched-mode power supplies
reacts very quickly to overcurrents
on the output side. Selective pro-
tection of individual current paths
in the secondary circuit via fuses
or conventional circuit breakers is
often ineective if the power supply
cannot deliver a brief overcurrent.
• Example:Low-voltage,
high-power and DP fuses
• High overcurrents required for fast
tripping
• In the example:
10-fold overcurrent (related to the
fuse nominal current):
• Tripping within range
30ms (best case) or
200ms (worst case)
Only 2-fold overcurrent:
• Tripping within range
2s (best case) or
> 100s (worst case)
Thermal Thermal and Magnetic Electronic
• Found in circuit breakers
or motor protection switches
• High overcurrents required
for fast tripping
• In the example:
3 ... 5-fold overcurrent for B-char-
acteristic and AC operation, addi-
tional DC safety factor 1.2 or 1.5
• Thus, in the worst case scenario,
a tripping current of 7.5 times the
nominal current is necessary.
• Ensure precision settings
• Reaction within a short time –
even at low overcurrents
• Protection of long cable runs and
small cross sections possible
Power
supply unit
R
Conductor
R
Fuse
R
Contacts
R
Ground fault
or R
Short circuit
K1
Loop Impedance
7.5
10
10
0,1
0.004
51
0.001
0.01
0.1
1
10
100
1000
10000
10 15
1
1
0.01
51
0.01
20 30103
B C D
0.1
1
10
1
10
20
40
60
t [s]
I/I
N
t
min.
I/I
N
t [s]
I/I
N
2 84 6 15
sec.
WHY SECONDARY-SIDE FUSE PROTECTION?
WHAT TYPES OF FUSE PROTECTION ARE THERE?
DP fuse = Device protection fuse