In regular service, passenger aircraft expect to be struck by lightning at least once a year on average. A great deal of modelling and testing is undertaken to make sure avionic equipment survives lightning strikes unscathed. This shielding effect of a metal enclosure means it is safer to remain within a metal-bodied car during a thunderstorm than to leave it. This 'ideal' system, which virtually eliminates problems with surges, is shown below. All equipment is metal-cased.
All equipment sits directly on a metal sheet to which it is electrically bonded.
Everything shares the same low-impedance zero volt reference. For good measure, the metal 'earth plane' is at ground level and connected to ground by a system of rods driven into the soil so that it is at local ground potential. There is no connection to other electronic systems. The system is physically small, a few square metres at most, so making the likelihood of a direct strike negligible. The purpose of the metal 'earth plane' sheet is to provide a low impedance to any induced currents which flow, resulting in very small induced voltages.