"Don't get confused by the similarities between 4 kV ESD testing, 4 kV fast transient burst testing and 4 kV surge. The voltages are the same, but the energy behind them is totally different. Dropping a small rock on your foot may hurt, but you will still be able to walk. Dropping a large rock from the same height will most likely cause severe damage to your foot. Doing this 250 times per second will reduce your shoe size permanently. When the surge boulder falls, you'd rather be somewhere else."