Ground transients are surges that most surge protectors simply can’t handle. A surge through the ground can range from an annoyance to a catastrophic event that can bypass most any surge protection system, making them an uncommon but substantial threat to mission-critical items. There are items on the market you can buy now to deal with these, however. The key is in knowing what to look for.
The key to dealing with ground transients is to filter them. This will require a different frequency device depending on the nature of the ground you are trying to protect. However, this is a difficult matter to resolve, and that is why it was a period of decades before any devices were patented to reliably work with different ground lines. The key is in filtering transients without interfering with the ground itself. There are now devices that can be mounted directly on the ground line to fulfill this purpose.
Older methods required systems that would minimize impedance, but these tended to be ineffectual at intervening with all ground transient events. Solid state devices were more generally effective, but their function could be substantially altered over time as current varied, making them unreliable. That is why these solutions were never approved for safety reasons.
The patented solution that meets regulatory requirements allows surge current to filter back through the transformer in the case of significant overage. This allows a device with very low impedance to filter much larger surges safely while still allowing for a heavy ground line.