Dimenzování a jištění elektrických zařízení - tabulky a příklady – Kříž Michal (2019)

Correctly and optimally sizing and securing electrical devices is not easy. It is always necessary to reconcile a whole range of requirements. Among these, two fundamental ones, namely ensuring the safety of the operated device and the overall cost-effectiveness of its implementation, are inherently contradictory. The goal is always to ensure that the device and the supply lines do not endanger their surroundings even under the most unfavorable operational and even fault conditions. On the other hand, our financial capabilities force us to ensure that the entire system is not oversized, unnecessarily expensive, or space-consuming. Electrical engineering regulations determine the safety of electrical devices. The device must not overheat excessively during overload, voltage drops on the supply must not exceed the permissible limit under any operating conditions, and protection through automatic disconnection from the source must respond within a sufficiently short time in the event of a fault. It seems that if the device and its supply are adequately sized, these requirements will be met. However, even with oversized devices, there is no guarantee that the device will meet safety standards. In this case, excessively large short-circuit currents can occur during a fault.