A direct lightning strike on a building is rare. The transient overvoltage it induces on power and signal lines is far more common — lightning a kilometre away can still induce damaging surges, and ordinary switching of large loads produces transients with similar character. IEC 61000-4-5 defines how to test equipment's ability to survive these surges, and the surge generator recreates the transient in a controlled, repeatable form.
Why Surge Testing Is Different From ESD Testing
ESD pulses are extremely fast (sub-nanosecond) and low-energy — the danger is edge speed, not total energy. Surge pulses are far slower (microsecond-scale) but carry substantially more energy, simulating genuine power transferred by a lightning-induced transient. Surge testing more often causes actual component damage rather than the software glitches typical of ESD testing.
The Two Combination Waveforms
1.2/50μs (voltage) and 8/20μs (current) combination wave. The standard waveform for power line and most signal line testing. Actual voltage and current delivered depend on the EUT's input impedance.
10/700μs (voltage) and 5/320μs (current) combination wave. Used specifically for outdoor symmetrical communication line ports — telecom cabling, where the induced transient has a different time profile than building power wiring. A generator built for one waveform isn't automatically suitable for the other.
Test Levels and Coupling Modes
Surge levels typically range from 0.5–4kV line-to-line and 0.5–6kV line-to-ground. Surges are injected through coupling/decoupling networks (CDNs) appropriate to the port type, and a surge generator's output impedance needs to switch automatically between values the standard specifies — commonly 2Ω for line-to-line and 12Ω for line-to-ground.
What's Actually Inside a Surge Generator
A surge generator charges an energy-storage capacitor, then discharges it through a pulse-shaping network into the EUT via the coupling network. A feature worth looking for, as in the LISUN SG61000-5, is a built-in oscilloscope letting the actual delivered waveform be verified directly, since real-world loading effects can shift it from the open-circuit specification.
Surge testing typically requires synchronisation with the AC mains phase angle, since equipment can respond differently to a surge at a zero-crossing versus a peak. A fully automatic generator handles this synchronisation without manual triggering.
A Practical Safety Note
Surge testing involves genuinely dangerous levels — generators commonly reach 20–30kV open-circuit voltage and several kiloamps of short-circuit current. Isolation transformers and a dedicated test enclosure are standard practice, since the EUT itself can fail energetically under surge stress.
Selecting Surge Test Equipment
For general commercial testing, a generator supporting 1.2/50μs/8/20μs, automatic impedance switching (2Ω/12Ω), phase-angle synchronisation, and up to 6–10kV covers most IEC 61000-4-5 test plans. For telecom or higher-severity work, a generator additionally supporting 10/700μs/5/320μs and higher ranges (up to 20–30kV) avoids needing a second instrument. Pairing the generator with correct CDNs for each port type is essential, not optional.