The data problem the 2002 edition had

The 2002 edition's empirical model was built from a real but comparatively limited test program — on the order of 300 tests. That data set covered a real but bounded range of system voltages, gap distances, and enclosure sizes. Outside that range, the 2002 equations were an extrapolation, not a measurement — which matters a great deal for equipment at the edges of what utilities and industrial facilities actually run.

What the 2018 test program did differently

The 2018 revision was preceded by a much larger, multi-year joint IEEE/NFPA testing program — roughly 1,800 tests across a wider voltage and gap range. That's not just "more data" in the abstract — it's data covering equipment configurations and voltage levels the 2002 model never actually measured, which is why the 2018 model can now natively cover more of the 208 V–15 kV range with equations grounded in test results rather than extrapolation.

Structural changes to the model itself

A few changes are structural, not just "different coefficients":

Electrode configuration became explicit. The 2018 edition formally defines five configurations — VCB, VCBB, HCB, VOA, HOA — and the equations depend on which one applies. The 2002 model had a much coarser notion of enclosure type. See our companion piece, Arc Flash Electrode Configurations, Explained, for what each one means and how much difference it actually makes.

Arcing current variation. The 2018 model calculates a range around the predicted arcing current and checks incident energy at both ends of that range, because a lower arcing current can sometimes mean a protective device clears the fault more slowly — which can produce higher incident energy than the "expected" arcing current would suggest. The 2002 model did not do this, which is one of the more consequential quiet gaps in older studies.

Enclosure size correction. The 2018 model explicitly accounts for enclosure width, height, and depth rather than treating "boxed equipment" as one bucket.

What this means if you have a 2002-vintage study

A study built on the 2002 model isn't automatically wrong, but it was built on a narrower tested envelope than the current standard — which matters most for equipment sitting near the edges of common voltage classes or enclosure sizes, exactly where the 2002 model was extrapolating rather than measuring. NFPA 70E already calls for arc flash risk assessments to be reviewed on a regular cycle and whenever the electrical distribution system is modified; a study still on the 2002 basis is a reasonable thing to flag for that review specifically, rather than assuming a study is current just because no equipment has changed since it was performed.