Overvoltage protection of low voltage networks
SPD (Surge Protection Device) selection criteria.
- permanent operational voltage Uc
- voltage protection level UP
- ability to absorb energy (Joule rating)
The network type designations given
have the following meanings:
a) The first letter – expresses the
relationship between the network layout and the earth potential
- T – direct grounding of a given point of the operational current circuit, usually a node (zero point)
- I – insulation of all live wires from the ground or direct connection of the grid system point to the ground through high impedance
b) The second letter – expresses the relationship between the non-live conductive parts and the potential of the earth
- N – direct connection of non-live conductive parts to a grounded point in the grid system
- T – direct connection to the ground of non-live conductive parts
c) The third letter, if present, indicates the relationship between the neutral conductor and the protective conductor
- C – the function of neutral and protective conductor is combined in one PEN cable
- S – the function of protective conductor is carried out by a separate wire independent from the neutral wire
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