Specifications

T4
Keep the lead length short
As the let-through or residual voltage of a SPD is
the primary measurement of a protectors’
effectiveness, special care needs to be taken when
hooking up the device. Indeed, the let-through
voltage is directly affected by the impedance of the
connecting leads, thus by their length and cross
section (see fig.17). Obviously, the performance of
the entire circuit decreases as this impedance
increases.
Increasing the conductor size will help to reduce the
impedance. However, as at high frequencies the
inductance is more important than the resistance,
reducing the wire length (thus reducing the
inductance) will have a much bigger impact than
increasing the cross section (= reducing the
resistance).
Also, increasing the cross section implies increasing
the installation cost, while reducing the length
implies reducing the installation cost.
T4.53
Surge arresters
Use Kelvin connections
Wherever possible, ordinary parallel connections as
shown in figure 17 should be avoided and Kelvin
connections as shown in figure 18 should be
applied. This way of connecting virtually reduces
the additional voltage-drop in the connecting wires
to zero, obtaining the best U
P possible.
Theoretically, since the terminals of the SurgeGuard
devices have a maximum capacity of 1x50mm
2
or
2x20mm
2
, Kelvin connection is possible up to 63A.
However, due to the excessive heating of the
terminal at higher currents, we advise not to use
Kelvin connections above 50A.
Install the SPD as close as possible to the up-
stream circuit breaker
Again in order to reduce the additional volt drop as
much as possible in the interconnecting wiring,
keep the length (L) of those wires as short
as possible (fig.19).
Install the SPD as close as possible to the
equipment to be protected
fig.16
fig.17
fig.18
fig.19
fig.20