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 pro-
tection as well. Furthermore, Machin-
ery Directive EN 60204 requires the
detection of hazardous ground faults
in control circuits and switching 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 can-
not deliver a brief overcurrent.
• Example: as found in
NH 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 safety factor 1.2 or 1.5
• Thus, in the worst case 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
4 A
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 [s]
I/I
N
t [s]
I/I
N
2 84 6 15
WHY SECONDARY-SIDE FUSE PROTECTION?
WHAT TYPES OF FUSE PROTECTION ARE THERE?
NH fuse = Low-voltage, high-power fuse
DP fuse = Device protection fuse