Protection levels and coordination between levels
The protection levels and inter-level coordination of SPD should comply with the following regulations.
a) When the relationship between the first-level SPD installed in the low-voltage power distribution system and the protected equipment cannot meet the following conditions, the second-level SPD should be installed at the distribution panel or in front of the equipment close to the protected equipment:
1) The length of the lead connecting the SPD does not exceed 50cm, the distance between the SPD and the device is less than 10m, and Uₚ is less than 0.8×Uw;
2) The length of the lead connecting the SPD does not exceed 50cm, and the distance between the SPD and the device is greater than 10m, but 2×U is still less than 0.8×Uw;
3) The length of the lead connecting the SPD exceeds 50cm, the distance between the SPD and the device is less than 10m, and Up/f is less than Uw;
4) The length of the lead connecting the SPD exceeds 50cm, and the distance between the SPD and the device exceeds 10m, but 2×Up/f is still less than Uw;
5) When there is no electromagnetic field interference generated by lightning discharge or internal interference sources inside the building.
b) When the second-level SPD cannot meet the conditions of a), a third-level SPD should be installed.
c) When there is no clear product installation guide, the line length between the switching SPD and the voltage-limiting SPD should not be less than 10m, and the line length between the voltage-limiting SPD should not be less than 5m. Otherwise, a decoupling inductor should be installed ( or resistor) component. When the manufacturer has made it clear that energy coordination measures are in place in its products, it may no longer require decoupling components.
d) The first-level SPD installed in the electronic signal network should be installed on the distribution frame at the entrance of the building. When the transmission cable is directly connected to the interface of the protected equipment, it should be installed on the equipment interface.
e) The method of installing second-level and third-level SPDs in electronic signal networks should comply with the provisions of a~c.
