First learn what an effective protector does. It never tries to 'block' or 'absorb' a surge. Effective protectors are only connecting devices to what does all protection.
Where are hundreds of thousands of joules harmlessly absorbed? Single point earth ground. Not any other ground. And that connection to earth must be low impedance (ie less than 10 feet). Protector is only a connecting device to what does all protection - earth.
Quality of that protection is defined by that low impedance (ie hardwire has no sharp bends or splices) connection to and the quality of those earthing electrodes. Often that earth ground must be upgraded to exceed code requirements. Code is only concerned with protecting humans. Earth ground is upgraded to also protect hardware.
Second, lightning (one example of a surge) is typically 20,000 amps. So a minimal 'whole house' protector is 50,000 amps. Those plug-in Siemens type protectors are smaller. So multiple ones must be installed.
That number defines protector life expectancy over many decades and many direct lightning strikes. Since effective protectors must never fail catastrophically. Only profit center protectors fail to increase sales and profits.
Third, that specification number is about protector life expectancy. Protection during each surge is defined by that low impedance (ie hardwire is not inside metallic conduit) connection to and the quality of single point earth ground.
Four, an AC electric utility demonstrates what must exist to have single point earth ground using good, bad, and ugly (preferred, wrong, and right) examples at
Tech Tips - Duke Energy . Select Tech Tip 8. Every incoming wire must be part of that solution.
If not obvious, protection is always about earth grounding a surge. Not its victim. Effective protection always means a surge is not anywhere inside.
