Series connection

This mode connects the SPD directly in series with the signal transmission channel, so that the surge current and signal flow share the same path. Its core value lies in ensuring the integrity of high-speed signals:

Applicable scenarios: High-bandwidth systems such as Gigabit Ethernet (≥1Gbps), USB 3.0+, HDMI 2.0, 3G-SDI video, and radio frequency (RF). These scenarios require impedance matching accuracy (±10Ω) and insertion loss control (<0.5dB). Series SPDs, with their ultra-low parasitic capacitance (≤1pF), prevent signal edge distortion and maintain eye diagram compliance.

Key technologies: A fail-open design (with built-in fusing mechanism) is required, and the grounding path must meet the low-inductance specifications of IEC 61643-21 (grounding wire length <0.5m, inductance <100nH). Over long-distance transmission, the series topology suppresses residual voltage oscillations caused by line inductance, making it suitable for precision scenarios such as industrial automation backbone networks and base station feeders.

Parallel connection method

This mode connects the SPD in parallel between the signal line and the ground line, and the normal signal bypasses the protector. Its advantages are adaptability to medium and low speed systems and simplified engineering modification:

Applicable scenarios: RS-485/422 (≤10Mbps), CAN bus, 4-20mA sensors, analog audio, and POTS telephone lines. These systems can tolerate high capacitive loads (typically 50-100pF) and can be installed in parallel without disconnecting the lines. They are suitable for lightning protection upgrades in existing systems such as fire alarms and building automation systems.

Key technologies: Performance is highly dependent on ground quality—ground impedance must be ≤0.1Ω, and the discharge path inductance must be <1μH (wire diameter ≥6mm²). A low clamping voltage TVS diode (e.g., ±5V@3A) must be used to ensure the residual voltage is less than 80% of the withstand voltage of the protected equipment.