TVS Selection for Lightning and Surge Protection: IEC 61000-4-5 Compliance Guide

IEC 61000-4-5 surge immunity testing simulates the high-energy transients produced by lightning's indirect effects and electrical switching operations on the power grid. Unlike ESD (single extremely fast discharge) or EFT (continuous burst of low-energy pulses), surge testing applies a single but very high-energy event using standardized 1.2/50 µs voltage and 8/20 µs current waveforms. Selecting an undersized TVS — one without adequate peak pulse power — is the most common cause of surge test failure, often resulting in the TVS itself being destroyed during the test.

This guide explains the surge waveform, the staged protection approach required for higher test levels, and specific ASIM TVS selection for each port type.

What Are the IEC 61000-4-5 Test Levels and Voltage Requirements?

Level	Power Line Open-Circuit Voltage	Signal Line Open-Circuit Voltage	Typical Application
1	±0.5 kV	±0.5 kV	Well-protected environment
2	±1 kV	±1 kV	Partially protected environment
3	±2 kV	±1 kV	Most common industrial standard
4	±4 kV	±2 kV	Severe environment (outdoor, high lightning exposure)

Two coupling modes are tested: line-to-line (differential, between L and N) and line-to-ground (common mode, between line and PE). Line-to-ground coupling is generally more difficult to pass because it requires both adequate TVS clamping and a low-impedance ground return path.

Why Does a Single TVS Often Fail to Meet Higher Surge Levels?

A surge protection device must satisfy two requirements that pull in opposite directions:

1. High energy absorption capacity (favors larger junction area, slower response)

1. Fast response time and precise low clamping voltage (favors smaller junction area, faster response)

No single component family optimizes both simultaneously. This is why surge protection at Level 3 and above typically uses a staged protection architecture combining multiple component types.

What Is the Staged Protection Architecture for Surge?

Power line input

│

[Stage 1: GDT (Gas Discharge Tube), 90–600V trigger voltage]

High energy capacity (kA range), but slow response (~100 ns) and high clamping voltage

│

[Decoupling element: inductor or resistor]

Limits current reaching Stage 2 before Stage 1 fully activates

│

[Stage 2: MOV (Metal Oxide Varistor)]

Moderate energy capacity, faster response (~25 ns)

│

[Stage 3: TVS diode]

Fast response (< 1 ns), precise low clamping voltage, lower energy capacity

│

Protected circuit

Why the decoupling element matters: Without sufficient impedance between stages, the TVS (fastest-responding, lowest energy capacity) may activate before the GDT fully ignites, absorbing energy intended for the GDT and potentially failing under the full surge current.

How to Select a TVS for AC Power Line Protection (220V)

For Level 3 or 4 testing on a 220V AC input:

AC L/N input

│

[GDT: 600V breakdown] ← primary stage for Level 4

│

[10 µH decoupling inductor]

│

[ASIM SMCJ440V, 1,500 W] ← secondary stage, precise clamping

│

Rectifier / protected circuit

SMCJ440V (VRWM = 440 V) accommodates the rectified DC bus voltage in a typical 220V AC system (which can reach approximately 310V DC after rectification, plus tolerance) without conducting during normal operation.

For Level 2 or lower testing, the GDT stage may be omitted if the SMCJ or equivalent SMB-package TVS alone provides adequate peak pulse power margin — verify with pre-compliance testing.

How to Select a TVS for DC Power Rails (24V, 48V)

DC rail surge energy is typically lower than AC line surge because there is no AC-coupling amplification effect from lightning's indirect coupling into the grid. A single-stage TVS is often sufficient for Levels 2–3.

DC Rail	Recommended ASIM TVS	PPM
24 V	SMCJ28V	1,500 W
48 V	SMCJ58V	1,500 W
12 V (industrial)	SMB06J15V	600 W
12 V (automotive, ISO 7637-2)	SM6S15V	6,600 W

For automotive 12V systems, note that ISO 7637-2 (not IEC 61000-4-5) governs load-dump transients, which carry substantially higher energy than typical IEC 61000-4-5 industrial surge levels — requiring the higher-power SM6S series.

How to Select a TVS for Signal/Communication Ports

Signal ports (RS-485, Ethernet, telephone lines) typically test at Level 3 (±1 kV) for line-to-ground coupling.

Signal line

│

[GDT 90V] ← required for long outdoor cable runs; can be omitted for short indoor runs

│

[ASIM SMA04J06B or SMA04J12B, bidirectional, 400 W] ← matched to signal voltage level

│

Transceiver IC

Select the TVS VRWM to match the signal's normal operating voltage range — for RS-485 (common mode range −7V to +12V), use SMA04J06B (VRWM = 6V) per the standard RS-485 protection approach.

What TVS Power Rating Corresponds to Each Surge Test Level?

Surge Test Level	Minimum Recommended TVS Power	Example ASIM Part
Level 1 (±0.5 kV)	400 W (SMA package)	SMA04J series
Level 2 (±1 kV)	400–600 W (SMA/SMB)	SMA04J / SMB06J series
Level 3 (±2 kV)	600–1,500 W (SMB/SMC)	SMB06J / SMCJ series
Level 4 (±4 kV)	1,500 W or higher (SMC or staged with GDT/MOV)	SMCJ series, or multi-stage

This table provides simplified guidance. Actual power requirements depend on line impedance (which determines actual current for a given open-circuit voltage) — precise sizing requires circuit simulation or empirical pre-compliance testing.

Common Surge Protection Design Errors

Error 1: Using only a TVS without front-end GDT/MOV for AC ports at Level 3+

A TVS alone often lacks sufficient peak pulse power for Level 3/4 AC line testing and will be destroyed by the full surge energy.

Error 2: Insufficient decoupling impedance between stages

Without enough impedance, the faster-responding TVS conducts before the GDT ignites, absorbing current beyond its energy rating.

Error 3: TVS clamping voltage exceeds the protected circuit's maximum rating

The TVS may function correctly (clamp the transient) but still allow voltage above the protected IC's absolute maximum rating to reach the circuit, causing damage despite "successful" TVS operation.

Error 4: High-impedance ground return path

TVS, GDT, and MOV all rely on a low-impedance path to ground to divert surge current effectively. A long or poorly connected ground trace leaves residual voltage too high even when the protection components themselves function correctly.

Frequently Asked Questions

Q: A design passes line-to-line (L-L) surge testing but fails line-to-ground (L-PE) testing. What is the likely cause?

A: L-PE testing requires a low-impedance path from the protection component to PE ground, plus adequate Y-capacitor or TVS coverage in the common-mode direction. Check: (1) whether the Y-capacitor connects to PE rather than signal ground, (2) the impedance of the PE ground path, (3) whether the TVS configuration covers both L-to-PE and N-to-PE directions.

Q: The TVS was destroyed during surge testing. Does this indicate the wrong part was selected?

A: Common causes: (1) insufficient power rating for the actual surge energy, (2) missing front-end GDT/MOV stage, forcing the TVS to absorb the full surge alone, (3) cumulative degradation from repeated test pulses without adequate margin. Recommend selecting a TVS with at least 50% power margin above the calculated minimum for surge-critical applications.

Q: Does ASIM provide IEC 61000-4-5 pre-compliance testing?

A: Yes. ASIM's in-house EMC laboratory provides free pre-compliance surge testing alongside ESD, EFT, and conducted/radiated emission testing. Contact ASIM at +86-400-014-4913 to schedule testing and receive component selection support.

About ASIM Electronics: ASIM (阿赛姆电子) is a Shenzhen-based manufacturer of TVS protection components, founded in 2013. Surge protection product line spans the full power range needed for IEC 61000-4-5 Levels 1–4: SMA04J series (400 W), SMB06J series (600 W), SMCJ series (1,500 W), SM6S series (6,600 W, automotive ISO 7637-2), and 15KPA/20KPA series (15,000–20,000 W, high-voltage EV/industrial). In-house EMC laboratory with free pre-compliance testing. Contact: +86-400-014-4913 | asim@asim.com.cn | Published: June 2026