Strike faking: how lightning can be simulated to check equipment is safe

Test pulses from lightning impulse generators can be used to ensure lightning protection is functioning properly

Lightning protection is mandatory for schools, high-rise blocks of flats, churches and factories in the UK. It is also essential for electrical equipment, the testing of which may involve using a portable lightning generator.

A lightning inspector’s annual check is mainly visual confirmation that lightning rods are intact, the necessary connections are in place and nothing has been damaged by lightning in the previous year. Inspectors check that surge protectors, which prevent lightning from overloading a building’s electrical circuits, are in place and working. Inspection may also involve physical testing, such as measuring the conductivity of lightning rods.

In the case of electrical equipment, testing can mean simulating the effects of a lightning strike. A lightning impulse generator is a type of Marx generator. This is essentially a bank of capacitors, perhaps the size of a small fridge. It has a special type of switch so it discharges extremely rapidly.

The generator produces a short pulse of millions of volts, which closely resembles the real thing. The big difference is not the voltage but the energy: an actual lightning strike is many thousands of times more powerful. But a test pulse ensures that lightning protection is functioning properly and that equipment will not suddenly stop working in the event of a bolt from the blue.

Cover photo:  Lightning over London. Lighning protection is mandatory for high-rise blocks of flats, among other buildings. Photograph: Guy Corbishley/Alamy