We all know, or at least should know, that the electric service panel is connected to earth ground. That connection can be via a ground rod, water pipe or metal well casing. Ideally that's the only place in your home where should be a conductor connected to anything electrical comes into your home. Let me give an example, one that took me years and many equipment failures to figure out. Cable TV. When cable TV was run on my street the cable company offered free installations. It was done by contractors in the cheapest way. Where's your TV? In the living room. We'll run the cable right through the wall there. OK? They did. Ground rod and lighting protection device outside right there on the wall right behind the TV. Is this OK. NO, NO, big mistake. There are now two electrical earth grounds in the house, the cable TV coax and the electric service entrance. The cable TV coax gets connected to your TV, cable modem, router, etc. This effectively connects the two earth grounds together, inside your home. Now, along comes a lighting strike, one that doesn't even have to hit your home. Big, big, really big currents are flowing in the earth. They find their way to your two earth connected grounding rods. It's highly unlikely the exact current will be at each grounding rod. If there is a different ground current in each, a current caused by the difference in potential will flow. Where? In your house. In the wiring that connects them. What's that? The cable TV coax shield, the green wire in all your electric outlets, the white neutral in your circuit breaker panel, etc. This flowing current, if it's large enough, and in a lighting strike it will be, will cause a voltage difference in the different ground wiring circuits. What happens? Puff, at the weakest point of connection, inside your electronics. Your TV, cable modem, VCR, etc.
The solution? One and only one point where earth ground enters your house. This means all, electric power, cable TV, satellite TV, telephone land line, electric sub-panel feeds to out buildings, wiring to your submersible water well pump, enter your house at the same physical point. AND all the lighting protection devices associated with each service, i.e. electric service bonded neutral, cable TV lighting protector, telephone company provided lightning protector, satellite TV dish ground, etc. use the same single ground rod circuit. All this is difficult to do. But after I did it, I stopped burning out TV's, cable modems, answering machines, well pumps, etc.
THINK what you have. Draw a schematic diagram of your grounding circuits. THINK of each place a metal conductor, that's connected to your electric devices comes into your home. There's a lot. Propane tank copper line? It's connected to your dryer's electric ground. Central A/C? The copper refrigerant lines go outside. It's connected to the condensing unit's electric ground. Etc. Good luck.