SPD when placing the control system in the secondary switchboard

When applied with a control system, SPD type 3 with a high-frequency filter is used, which not only protects the system against overvoltage but also against noise that occurs in low voltage networks. The connection of SPD type 3 with RF filter can be done as follows.

Fig. 1 Example of connection of coordinated protection SPD Type 2 and SPD Type 3 with HF filter

Notes:

1. The example shows the coordination of the SPD (observance of the correct cable lengths) between the SPDs in the individual switchboards (switchboards).
2. If the coordination distance between the individual stages is not observed, it is necessary to install RTO isolating chokes. (see this article).