For optimal protection of electrical systems, it is necessary, in addition to the use of differential switches and circuit breakers, to install overvoltage dischargers or SPDs (Surge Protection Devices). These components, positioned inside the main and/or the secondary switchboard, are designed to protect the equipment, systems and devices, from overvoltage caused by direct currents, switching currents or induced by lightning, during thunderstorm activity.

The surge arrester is one of the most important parts of the protection system. Belco SPDs are advanced class 1 protection systems, with magnetic blow spark gap technology and have been tested to be resistant to the consequences of atmospheric phenomena and in general to any overvoltage, releasing a very low residual voltage.

Belco overvoltage and lighting arresters are characterized by:
- high precision of the trigger voltage with any kind of overvoltage;
- restoration of the normal operating conditions by interrupting the arc current at its first passage through zero after the end of the overvoltage;
- capability to withstand currents with a peak value up to 100 kA (10/350 µs), 80 As charge and a specific energy of 1.25 MJ/Ω;
- self-regeneration.

Thanks to its characteristics, the arrester does not have to be replaced, Its functionality is guaranteed up to 100 “hits” and more, without any intervention, differently from what happens with other surge protection systems.

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Typically, Belco SPDs are installed at the gataway of the electricity grid to protect the isolation transformer, as shown in the figure below.