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Special Edition: February 2015 Wiring Matters cover image

Surge protection

Steven Devine, Engineer at the IET, recently visited DEHN and SÖHNE in Germany for the purposes of understanding progress in surge protection devices. Here, he writes about his experience.

I recently had the opportunity to visit DEHN and SÖHNE at their impulse current laboratory in Neumarkt, Germany to witness surge protection devices (SPDs) in action. I was joined by several others from the surge protection industry all eager to see the demonstration. It was made very clear from a short presentation that lightning protection/separation and surge protection go hand in hand with one another. While lightning protection will prevent the integrity of the structure from being damaged, the SPD will provide a measure of protection for electrical equipment within the structure.

Both lightning strikes and electrical switching can inject what are called transient overvoltages into an installation. Transient overvoltages are usually only a few microseconds in duration. However, at their peak value they can reach 6kV. Electrical equipment can be adversely affected from these surges, particularly electronic devices such as computers and servers for data storage.

SPDs, when selected and installed correctly, can significantly reduce the effects of these transient overvoltages. At DEHN laboratories it is possible to test the protective function of SPDs with lightning currents up to 200 kA (10/350 μs). We were shown four examples of lightning strike surge protection using Type 1 SPDs:

  • the first, an older SPD, was subjected to 30KA, however, it had not been designed to withstand the applied force. It reacted as expected, diverting the surge to earth but was damaged beyond repair in the process.
  • the second was a fully working SPD with an indicator to show when the device had expired. There was little to see when the surge was induced on this SPD as it functioned correctly, protecting the circuit as it was designed to do. The indicator remained green (still in working order). 
  • the third was a correctly installed but underrated SPD. The results were astonishing: the SPD itself was obliterated, creating flames and blackening the surrounding area. The installation, however, remained intact.
  • the final example used a sufficient but incorrectly installed SPD subjected to a 70KA surge. The SPD suffered from various installation defects that were a result of poor installation techniques and as such it did not comply with the manufacturer’s instructions. The results were devastating: the entire housing for the installation was destroyed, the cable was torn from its containment and its conductors split through the insulation and sheathing, creating a significant amount of damage. However, the SPD itself remained intact and in good working order.

It was clear from the demonstration that, provided they are correctly selected and installed according to manufacturer’s instructions, SPDs can be a valuable means of protection against lightning strikes.


Please see our article on Separation from lightning conductors.