Faraday Cages and Lightning Safety

Physics, Conducting Enclosures, and Protection in Electrical Storms

May 9, 2008 Paul A. Heckert

An enclosed metal shell acting as a Faraday cage can offer protection from lightning and other electrical effects.

Cars, Airplanes, and Lightning Strikes

Aircraft are often struck by lightning yet we don't hear about victims who are killed when their planes are struck by lightning. People often say that a car is a safe place to wait out a severe electrical storm. Why? In both cases people are relatively safe because they are inside a hollow conducting shell.

Faraday Cages

A Faraday cage is an enclosed hollow shell made of an electrical conducting material. If there is a large electric field outside the conducting shell, the electric charges on the shell will move around and rearrange themselves until the electric field inside the shell is zero. Therefore a Faraday cage acts as a shield for large electric fields or for electromagnetic waves. Even if a Faraday cage experiences the large electric fields of a lightning strike, the electric field inside the Faraday cage will be zero. Hence a Faraday cage makes an effective shield against lightning strikes.

Lightning Safety

An aircraft with a fuselage that is made of aluminum, or any other electrically conducting metal, will form a Faraday cage around the pilots and passengers. If the plane flies through an electrical storm and is struck by lightning, the electric field inside the hollow metal fuselage remains zero and the occupants are safe.

That is true as long as they are not in electrical contact with the exterior. For the electric field to be zero inside the Faraday cage, the electric charges must rearrange themselves on the surface. These moving charges on the outside of the Faraday cage can produce strong electric currents. Hence the occupants of the airplane should not be in electrical contact with the outside shell of the aircraft.

A metallic car or other vehicle can also be a safe place in an electrical storm for the same reason. A car with a fiberglass body or a cloth top convertible will not form a Faraday cage, however any vehicle with an enclosed metallic shell will. If caught in a severe electrical storm while traveling by car, wait for the storm to end inside the hollow metallic car. Stop and turn off the engine. Sit inside without touching anything that is metal or in electrical contact with the outside of the car. That will be safer than leaving the car and waiting outside.

If there is a lightning strike, depending on the severity of the strike, the car and its electrical wiring may be damaged. However the Faraday cage effect provides the best protection possible to passengers if the vehicle experiences a lightning strike.

Further Reading

Hecht, E., Physics:Algebra/Trig, Brooks/Cole, 1997.

Knight, R.D., Physics for Scientists and Engineers with Modern Physics, Pearson, 2004.

Wilson, J.D., Buffa, A.J., and Lou, B., College Physics 6th ed., Pearson, 2007.

The copyright of the article Faraday Cages and Lightning Safety in Physics is owned by Paul A. Heckert. Permission to republish Faraday Cages and Lightning Safety in print or online must be granted by the author in writing.

Lightning Strikes Eiffel Tower 1902