'When the attraction between these charges is strong enough, the air becomes ionised and breaks down to create a path for the current to flow and that's when we see lightning.' 'The negative charges at the cloud's base then attract positive charges that accumulate on the ground's high points such as hills, tall buildings and trees. As a result, clouds becomes positively charged on top and negatively charged at the bottom,' explains Phung. 'In a thunderstorm, wind turbulence in clouds causes ice crystals and water droplets to collide. 'But these surges produce nowhere near the same amount of voltage and current as that caused by lightning, a giant discharge of electricity produced during a thunderstorm,' says Dr Toan Phung, a senior lecturer at the School of Electrical Engineering and Telecommunications, University of New South Wales. It can be caused by faulty wiring, downed power lines or the sudden and heavy use of high power electrical devices such as air conditioners during a heat wave, which can upset the steady supply voltage from the electricity network. A power surge is an abrupt, large increase in voltage or current in the power supply that typically lasts a fraction of a second.

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