It seems like something out of a horror movie but it is not impossible for your car to get zapped by lightning if you are driving a cabriolet in a storm and the soft top is not raised yet (you would not leave it down for long, would you?).
However, occupants of the new Mercedes-Benz CLK-Class Cabriolet will be just as well protected against lightning as passengers in cars with a rigid roof. This was one of the findings of an extensive series of tests commissioned by Mercedes-Benz and performed by the Institute for High Voltage and Power Engineering at Berlin’s Technical University in Germany.
The state-of-the-art steel and aluminium design of the CLK soft-top – featuring main mounts that are each fastened to the car body at three points – shields the car interior from the powerful electrical fields generated by lightning strikes. In the event of such a strike, the longitudinal struts and cross members that make up the soft-top frame assembly act like a Faraday Cage, thus allowing the electrical current to flow towards the outside of the frame and ensuring that the car interior remains a “field-free zone”.
This principle was discovered by the British physicist Michael Faraday at the beginning of the 19th century and still forms the basis for all sophisticated lightning protection systems to this day.
During the series of laboratory tests carried out at the institute, scientists discharged several dozen lightning impulses across the CLK Cabriolet using powerful capacitors connected in series. Lightning impulses of up to 1.4 million volts were achieved during the course of these tests.
Measurement of the electrical field strength inside the closed CLK Cabriolet confirmed the protective effect of the soft-top structure acting as a Faraday Cage: the lightning current was guided harmlessly to ground via the soft-top frame assembly, the car body and the tyres.
Thanks to reliable shielding, the crucial electronic systems which manage things like the ABS and airbags on board the CLK Cabriolet also proved immune to the powerful electromagnetic field generated by the lightning current in each of the tests.
Interest in this issue is timely as in the past year, there were some 2.9 million cases of lightning discharge during storms over Germany, Austria and Switzerland, compared to around 2.2 million cases in 2001… something going wrong with the Earth’s Core?(as the movie suggests). The highest lightning incidences were recorded in the months of June, July and August. Lightning is discharged around one million times per hour above the Earth’s surface.