Specifications

T4
T4.49
Surge arresters
The SGC40 has a 15µH coil, capable of conducting
40A, included in the range for this purpose.
Figures 9 and 10 are illustrating the effect of
cascaded MOV’s.
Figure 9 shows the clamping of a 20kA-270V MOV
alone. When the device is hit with a standard 20kA-
8/20 impulse wave (red curve), the voltage at which
the MOV clamps is 1.68kV (green curve).
Figure 10 shows the clamping of the same 20kA-
270V MOV in parallel with an 80kA-320V MOV up-
front. The interconnection between the two MOV’s
has a length of 1m and a cross-section of 32mm
2
.
Applying the same standard 20kA-8/20 impulse wave
(green curve) to this cascade, the voltage at which
the 20kA-270V MOV clamps is much lower (900V)
and much more stable (yellow curve).
Selection of up-stream circuit
breaker
Eventhough all MOV-based SurgeGuard SPD’s
incorporate internal protection (thermal fuse), as a general
rule, a circuit breaker or fused disconnect should be
installed up-stream of the SPD. In all cases, even in the
case where a general circuit breaker is already installed,
it’s advisable to add a circuit breaker (F2) just up-stream
of the SPD, in a selective way (fig.11). This provides a
means of disconnecting the SPD and not the entire
fig.9
fig.10
installation should the surge arrester fail. It also allows the
disconnection of the SPD for service or maintenance.
To be effective, the circuit breaker or fuse directly up-
stream of the SPD should be capable of cutting the
theoretical short-circuit current at the place where the
SPD is installed. In other words, the short-circuit
current interrupting capacity of the circuit breaker
should be at least equal to or preferably higher than the
calculated short-circuit current.
For the different values of I
MAX, table 4 shows the
necessary short-circuit interrupting capacity of the up-
stream circuit breaker. These values were obtained by
calculating the short-circuit current with only the short
circuit resistance of the SPD as the limiting factor.
An important consideration here, is that these are
worst case values, because in a real installation
several other resitances add up to the short-circuit
resistance of the SPD, and therefore decrease the
short-circuit current even further. The size of the
circuit breaker will not affect the performance of the
SPD. The circuit breaker size should be co-ordinated
with the connecting wire and should be sized
accordingly to the applicable National Electrical Code.
Features and benefits
What can be seen from the outside
Photo 1 shows a single and multipole SurgeGuard
SPD. As always for the Elfa+ range of products, the
main characteristics are printed in the upper part
of the front of the device
1 . These are:
-I
MAX
- Class
-U
P at INOM
- Operating voltage U
N
- Wiring diagram
- Single or multipole configuration.
The I
MAX of the SurgeGuard SPD’s goes from 20kA
over 45 to 65kA for the plug-in class 2 devices, up
to 80kA for the monobloc class 2 devices and up to
100kA for the class 1 devices.
300 mA
EP30
C16/C20
F2
SG 80kA
EP30
C16/C20
300 mA
30 mA
SG 20kA
F3
SG 45kA
or 20kA
fig.11
SPD
I
MAX
80kA
45kA
20kA
green: residual voltage
red: 8/20 current impulse
blue: residual voltage after 1st stage
yellow: residual voltage after 2nd stage
green: 8/20 current impulse
red: current through 2nd stage
EP100
EP60
EP30
Short-circuit interrupting capacity
Table 4