When Lightning Strikes

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One of the many myths surrounding lightning is that it never hits the same place twice. In reality, if the circumstances that facilitated the original strike remain constant in the area, then the laws of nature will encourage repeated strikes.

The Empire State building is struck on average 23 times a year. Chicago’s Sears Tower gets struck an estimated 50 times a year. It’s true that because lightning strikes initiate miles above the earth, objects on the ground have far less influence on where a strike will occur than most people think, but nonetheless there are factors that can increase strike rate. Extremely tall structures like towers and skyscrapers are more susceptible because they significantly reduce the insulating air gap between cloud and ground. Isolated objects have a greater chance of getting struck because the downward “feelers” of a strike, called the stepped-leader, have a better chance of hitting a standing object in the strike field before they hit the ground.

Lightning is arguably the single most destructive external over-voltage event that can happen to your system. Lightning strikes will regularly exceed 100,000 volts and 40,000 or more amps. Without proper circuit protection, even one lightning strike can destroy an electrical system, and many large scale electrical systems like power lines, switching stations, and power plants are built in areas with increased likelihood of strikes. Often they are among the tallest structures in the area, and are generally set away and in the open. Many outdoor electrical systems ionize the air around them as a byproduct of normal functioning, making the air more conductive. These systems need to be able to withstand multiple strikes in a single event, as well as over extended periods of time, without failing.

Thankfully, manufacturers are developing increasingly sophisticated surge arrestors to reroute over-voltage events safely to ground. Many of these components are specifically geared towards massive over-voltage events like lightning strikes, and also contain multi-strike capabilities. During a multi-strike event, your first line of defense will be the strength of your suppressor, usually a diode, diode array, varistor, or gas tube. Products like the LSP10 module series from Littelfuse offer varistors that are composed of radial leaded metal oxide and that have a thermally activated element that allows them to open in the event of overheating. Many solutions will have a combination of suppressors that act as multiple barriers, passing overloads down the line if they are destroyed.

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Your second line of defense is catastrophic disconnect. Littelfuse LSP05G module solutions are thermally protected and designed with built in disconnects, so in the event of catastrophic failure the system will become separated from the power source entirely and remain protected. A third lead in these solutions allows for engineers to devise an indicator that the system is off-line for quick monitoring and replacement.

Catastrophic system failure doesn’t have to be. With the right surge arrester technology your system can remain protected no matter what kind of voltage nature throws at it.

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