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Installing surge arresters in
a box or cabinet
General installation
rules
Dimensions
Section 10
Connections
These must be as short as possible. In fact, one of the essential characteristics for
equipment protection is the maximum level of voltage that the equipment can
withstand at its terminals. A surge arrester with a protection level suitable for the
equipment to be protected should be chosen (fig. 35). The total length of the
connections is L = L1 + L2 + L3. It represents an impedance of roughly 1 µH/m for
high frequency currents.
Application of the rule
∆
U = L
with an 8/20 µs wave and a current of 8 kA leads to a voltage of 1,000 V peak per
metre of cable.
∆
U = 1.10
-6
x 8.10
3
= 1000 V
8.10
-6
Fig. 35 - surge arrester connection: L < 50 cm
This gives U equipment = Up + U1 + U2.
If L1 + L2 + L3 = 50 cm, this will result in a voltage surge of 500 V for a current
of 8 kA.
Wiring rules
Rule 1
The first rule to be respected is not to exceed a distance of 50 cm when connecting
the surge arrester to its disconnection circuit-breaker. The surge arrester
connections are shown in figure 36.
Fig. 36 - diagram of the connections
di
dt