Novaris surge protection devices are designed to protect against both common mode and transverse mode surges.
A common mode surge appears as a voltage on all lines with respect to earth. These cause insulation breakdown.Earth potential rise and induced voltages are predominantly common mode disturbances.
A transverse mode surge appears as a voltage difference between the incoming lines. This causes damage to the input stages of electronic equipment. LV distribution systems, like the TN-C-S (MEN) system, produces transverse mode disturbances because the neutral conductor is earthed at the point of entry.
The following table provides a list of standard impulse voltage withstand levels for 230/400V based electrical equipment. The table is sourced from IEC 60664-1.
The rated impulse voltage of electrical equipment is the maximum transient voltage that the equipment is designed to withstand without insulation breakdown. The table above relates to insulation breakdown, namely the withstand voltage between each line and earth. The line to line breakdown voltage, resulting in component damage, is generally much lower than this; typically for 230/400V mains powered equipment it is around 700-800V.
When designing a surge protection scheme for a given site, it is important that the surge protection devise selection provides a residual voltage lower than the impulse voltage rating of the equipment being protected in all modes, namely line to line and line to earth.