What is Induced Electro-Magnetic Force?
INDUCED EMF are excessive voltages are induced into electrical wiring (which acts like an antenna) by nearby lightning strikes.
Particular care should be exercised when using solar panels since their large conductive surface area acts like an antenna that couples lightning induced emf directly into your electrical system.
Mutual coupling in wiring harnesses of vehicles and vessels can induce voltages in circuits that are electically isolated from one another. A typical example of this is where dual batteries are used. One battery is used to supply high loads to start the engine or run a heavy motor, while the other is used for electronic equipment. The theory is that heavy transients generated when starting an engine will not affect the electronics powered by the second battery. But, most often, the wiring for both systems is run adjacent to each other and this allows coupling of spikes from the 'starting' power system to the 'electronics' power system even though there is no physical or electrical connection between the two.
In the marine world, people often claim they have been hit by lightning which caused the loss of all electronics on board. However, further investigation usually finds that there was no direct strike to the vessel but rather damage was caused by induction from a nearby strike. "Nearby" is usually defined as 'within 1000 metres' (approx. 0.6 mile), but damaging voltage levels have been measured in electrical storms at ranges of 1.5 miles or more.
Polarization is also a factor. A horizontal strike from cloud to cloud induces a greater voltage in an electrical system cable that is laid horizontally. Peak voltages are measured when the wire is parallel to the direction of the lightning strike.
Likewise, a vertical lightning strike from cloud to ground induces maximum voltage in vertical wires - like those run up a mast to navigation lights.
Several hundred volts of lightning induced emf are frequently measured in moderate electrical storms. In areas of severe thunder activity, higher levels have been measured.