Industrial applications include various types of equipment that need to be protected from the effects of surges. They are costly to the company owner: the price may be enormous and the failure, or even replacement, of those devices would incur major financial loss, possibly putting the very existence of the company at stake. The key aspects, from the perspective of trade unions, are the employees: they operate electrical equipment and, in the event of a surge, their lives might be at risk. The facts mentioned above, as well as other causes, represent substantial reasons why one should seek protection from surges. This function uses internal and external protection from lightning, such as the air terminals, grounding, protective busbar, surge suppressors, all jointly referred to as surge protection devices, SPD. There are a number of companies that produce a plethora of devices, yet not all of them are suitable for industrial applications.The heart of it all, as the case typically is, lies in a directive or a legal requirement. In this specific situation, it is Czech Technical Standard SN EN 62305 Lightning Protection, Parts I through 4. The text also defines individual types of loss, risk, lightning protection systems as well as level of lightning protection. There are four levels of lightning protection (I through IV) which specify the parameters of lightning; the protection levels are the function of the risk level. In most industrial applications, the building is classified Level I or II. This corresponds to the peak values of lightning current Iimp (current impulse with parameters 10/350 µs) being as high as 200 kA. A qualified estimate suggests that 50 % of the overall Iimp current is arrested by the air terminals and delivered into the grounding system. The remaining 50 % becomes equally distributed among the inputs (i.e. among the external contacts entering the building), typically to the IT and communication cables, metal piping and LV power supply cables.