How to filter out power line spike interference in a concentrator?

Transient high-voltage spikes on power lines caused by load switching or lightning strikes can damage the concentrator's carrier coupling circuit and power supply. Filtering requires multiple stages of protection and filtering. The first stage of coarse protection uses a gas discharge tube (GDT), such as a 2R600L-8×6 GDT (DC breakdown voltage 600V) connected in parallel between the L/N lines. The second stage of clamping uses a TVS diode, such as an SMCJ33CA (bidirectional, Vrwm=33V). The third stage of filtering uses a combination of a common-mode inductor CMZ1211-501T and an X capacitor (0.47μF). For the carrier coupling port, an additional 7D390K varistor is connected in parallel on the primary side of the coupling transformer. On the PCB layout, the protective devices are placed close to the power input and coupling terminals. This synergistic protection scheme can withstand the IEC 61000-4-5 combined wave test (common-mode 4kV, differential-mode 2kV) and attenuates the amplitude of incoming board-level spike voltages by more than 40dB.