EMI/EMC Academy ~30 min Interactive

The EFT Waveform, Bursts & Test Levels

The 5/50 ns pulse, the 5 kHz/100 kHz burst packets, and the ±0.5–4 kV level classes. Knowing the waveform tells you exactly what your protection must be fast enough to catch.

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The individual EFT spike is defined as a 5 ns rise time and a 50 ns duration (to 50%) into a defined load — extremely fast. That nanosecond edge means the transient's energy reaches well into the hundreds of MHz, so any protection has to be fast and low-inductance; a slow TVS or a long ground lead simply won't respond in time.

5 ns rise 50 ns to 50%
The single EFT pulse: nanosecond rise, tens-of-ns decay (illustrative).

Pulses are grouped into bursts: a packet of spikes lasting ~15 ms repeated every 300 ms. Within a burst, the pulse repetition rate is 5 kHz (classic) or 100 kHz (per later editions, closer to real switching). The repetitive hammering is what makes EFT so good at finding firmware and timing weaknesses.

Because bursts repeat, an intermittent upset will recur many times during a test — making EFT reproducible on the bench, unlike a one-off field glitch.

Severity is set by level classes, typically ±0.5 / 1 / 2 / 4 kV. Power ports are usually tested at a higher level than signal/control ports, and the applicable level comes from the product's generic or product-family standard (industrial environments demand more than residential).

Common mistake: testing only the mains port. Long I/O and control cables are prime burst entry points and have their own (often lower) required level via the capacitive coupling clamp.
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