CLK Cabriolet: reliable lightning protection when soft-top is raised

Apr 23, 2003
  • Series of laboratory tests at Berlin's Technical University
  • CLK Cabriolet's soft-top frame acts as a Faraday Cage
In the middle of a storm with the soft-top down, occupants of the new Mercedes-Benz CLK-Class Cabriolet are 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.
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 (1791-1867) at the beginning of the 19th century and still forms the basis for all sophisticated lightning protection systems to this day.
Lightning impulses of up to 1.4 million volts
During the series of laboratory tests carried out at Berlin's Institute for High Voltage and Power Engineering, 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 electronic systems on board the CLK Cabriolet also proved immune to the powerful electromagnetic field generated by the lightning current in each of the tests.
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. The highest lightning incidences were recorded in the months of June, July and August. With over 190,000 incidences, June 20 was Germany's most prolific day for lightning in the year 2002. Lightning is discharged around one million times per hour above the Earth's surface.