Militaries and a handful of civilian labs test equipment in EMP simulators and with pulsed-current injection. Standards bodies have waveforms for the early, intermediate, and late parts of a high-altitude burst. The work is detailed, expensive, and mostly invisible to people buying a home inverter.

The early part is a fast, sharp field. The intermediate part is closer to a lightning-like surge. The late part is the slow pulse that drives current in long lines, the cousin of a geomagnetic storm. A test that covers one of them says nothing automatic about the other two. That is why “we tested it” is not yet an answer.

Simulators large enough to illuminate a real piece of equipment are rare, booked, and priced like the specialized facilities they are. Injection tests on a port or a cable are more common and still not a weekend project. Most of the civilian market never goes. The inverter on a hardware-store shelf was built to a safety standard for daily use, not to a pulse standard nobody required.

Absence of a test is not proof of fragility, and a marketing line that says “EMP hardened” without a standard and a level is not proof of anything. Ask what waveform, what amplitude, and what failed in the test. If the seller cannot answer, you are buying a mood.

Some untested gear will shrug. Some will not. You cannot know which from the font on the box. A useful answer names a standard, names the level, and says what happened to the device — it worked, it upset and recovered, or it failed. Silence is the tell.

Nationally, the same skepticism belongs on untested claims that the grid is “basically fine.” Fine relative to which waveform?

A grid study that models the late pulse and ignores the fast field, or the reverse, is a partial sentence. So is a vendor brochure. The craft is matching the claim to the part of the event it actually covers, and saying so in words a buyer or a regulator can check.