There are basically two types of powerline surge technology, patented Series Mode and the older Shunt Mode (so-called hybrids are usually Shunt Mode). The Shunt Mode technology was developed over thirty years ago to protect standalone equipment, but this older technology is no longer suitable for modern sensitive interconnected equipment.
Shunt Mode suppressors are still very common because this older technology is inexpensive to manufacture with high profit margins, and as long as people can be seduced by the low prices, these products will continue to be sold. They generally pert powerline surges to the safety ground wire, using circuits described as “All Three Modes of Protection”. The resulting surges perted to the ground wire can exceed 1000 volts, exposing sensitive motherboards and data boards to surge disruption, degradation and damage.
This surge voltage on the ground wire varies along the length of the wire. When equipment such as modems, printers and other computers are interconnected, the interconnecting cable creates a “ground loop”. If the surge induced on the safety ground wire of one computer is 1000 volts and the surge induced on the safety ground wire at another location is 600 volts, then the difference of 400 volts is fed into the interconnecting cables causing the disruption, degradation, or damage.
While large surges will cause damage, small surges can result in data problems such as lock-ups, data errors, and “mysterious problems.” It is better to avoid Shunt Mode surge suppressors that claim “All Three Modes of Suppression” than to try and live with the problems they cause when they pert surges to the ground wire.