Surge Protection FAQ

Establish the impulse withstand voltage Uw of the equipment (1.5 kV, 2.5 kV and 4 kV are common for 220/380 V equipment), then specify an SPD with Up not above 0.8×Uw. Lower Up gives better protection, usually at the cost of a larger device.

The test waveform and the installation point. Class I devices are tested with 10/350 µs and rated by Iimp; they belong where part of the direct lightning current may enter, such as the main incoming board or feeders to roof-mounted equipment. Class II devices are tested with 8/20 µs and rated by In / Imax, and are used in sub-distribution boards and at equipment.

When an SPD fails in short-circuit mode the installation sees power-frequency short-circuit current that the upstream device has to clear, while that same device must not operate on lightning impulses. A back-up protector is designed for that combination and must be matched to the SPD.

Ucpv must be selected for the maximum DC voltage, and the device must be able to extinguish DC arcs. A Y-connection with both poles to earth is common. Combiner box, inverter DC and AC sides and the substation are protected separately, and AC SPDs must not be used on the DC side.

Yes. Keep the conductors at both ends as short and straight as possible — a total length below 0.5 m is common practice — avoid sharp bends and avoid running them parallel to phase conductors over long distances. The voltage drop across the lead inductance adds directly to the residual voltage at the equipment.

A dedicated lightning earthing installation is commonly required to be below 4 Ω, with stricter limits in sectors such as telecom and data centres, while a common bonding network is usually required below 1 Ω. The applicable standard and soil resistivity decide the value; deep wells, earthing modules or soil replacement help where resistivity is high.

Most modular SPDs have a status window (typically green for healthy, red for failed) and a remote signalling contact. Replace the module rather than removing it and leaving the position empty. Devices with status monitoring or lightning current monitoring report the strike counter and module status on the platform.

A Rogowski coil or shunt captures the lightning current waveform; the data logger processes it and uploads over RS485, Ethernet or a wireless link, recording time, amplitude, polarity, number of strikes and SPD status for later analysis.

Fit matching SPDs to the power, video or network lines separately, and choose a PoE-capable device where PoE is used. Bond and earth the camera poles and the rack equipment, and protect metal masts against direct strikes rather than protecting only the equipment room.

Yes. Check the status indicator, terminal tightness and earthing before each lightning season and record the strike counter. Shorten the interval for outdoor installations or regions with frequent thunderstorms, and replace failed modules immediately.

An SPD needs a low-impedance path to earth to divert the lightning current. Where no reliable earth exists, install an earthing electrode or a common bonding network first — otherwise the SPD cannot work and may itself become a hazard.

Yes. Send us the single-line diagram, equipment list, mounting positions and location and our technical team will propose a configuration. For routine enquiries we reply within one working day.