Transient Currents

Hello.

My question is out of curiosity and pertains to transient currents and their possible effects on any electrical equipment. For example, The various electrical components(infotainment systems, headlights, radio etc) in a car are "grounded" on the chassis, If a live wire from a electricity pole carrying high current were to fall on my car, what effect would it have on the components in the car? would the high current cause damage to the components? what path will the current take? and is there a possibility for the high current to reach the component through its 'grounded' terminal? Could someone please clarify/explain the outcomes? Thank you.

You are curious about an interesing topic! Ground, shielding, ESD, conducted and radiated emissions, transient protection, etc. I'll take a stab at a general answer.

A high voltage line would probably arc through the thin paint layer and to a conducting chassis. Depending on the insulation your tires provide from ground, and the air gap between the chassis and ground, the high voltage may jump that gap, and current would flow through the chassis. If insufficient to jump, the car chassis would charge to the line voltage. (Think of a bird landing on a single phase power line.) If the power line was AC, some amount of current would flow anyway due to the capacitance from your car to earth ground.

While the chassis is charged, all modules tied to the chassis will follow the chassis voltage and little or no voltage difference would occur between modules. While current is flowing through the chassis, it can induce currents on wiring which interconnects modules. Depending on the magnitude of the induction and the impedance of the circuit endpoints, voltage can be induced at the circuit endpoints. Components can be damaged. If a low impedance at a circuit endpoint if from a clamping diode to battery voltage for example, it can be damaged from the induced current flow.

The ideal case is keep current flow out of modules, keep modules at the same potential, and connect modules with dielectric cables (fiber optics). There are many standards for testing and qualifying electrical modules for vehicle use. SAE standard are what are used in the US.

Thank you very much for your reply and for having taken the time to explain. I assume same would be the case say if lightning struck my car. "If a low impedance at a circuit endpoint if from a clamping diode to battery voltage for example, it can be damaged from the induced current flow". Does this mean the modules will not be damaged if a high impedance is maintained at the circuit endpoints?

No, devices such as clamping diodes are used to provide a low impdance to ground (or a voltage supply, which is an AC short circuit). High impedances at circuit endpoints will develop large voltages for a given current flow, and overvoltage also damages devices. Hopefully this is more clear.