Lightning strikes cost US insurers $US798 million ($769 million) in losses during 2009, according to an assessor of electronics claims.

Zap Consulting says there are more than 20 million “cloud-to-ground” strikes a year, and the reported losses do not include out-of-pocket expenses paid by businesses for damage not reported to insurers.

“We often think of lightning damage as what happens when lightning strikes a tree, structure, or wiring,” a Zap spokesman said. “But a lightning strike current can extend into underground wiring and pipes as well as above ground power, cable and phone lines.

“Lightning can damage electronics and equipment a mile or more from the actual site of the strike due to the significant strength of a lightning current.”

Electronic equipment has become the number one asset in dollar value for homes and businesses in the US.

According to Zap, US consumers spent more than $US144 billion ($138.7 billion) on technology in 2011.

There is no data on lightning strikes in Australia or what they have cost insurers, an Insurance Council of Australia spokesman told insuranceNEWS.com.au.