Currents on electric installations inside of buildings in case of lightning equipotential bonding at the roof

The main objective of this paper is to evaluate the maximum share of the lightning current, which flows on electric installations inside of buildings. The electrical conductors are equipotentially bonded to the external lightning protection system (LPS) at the roof level. A variety of wiring in typical buildings is analyzed using the computer code CONCEPT II. The transferred charge is the most important parameter for the selection of the surge protective devices (SPD). For a single conductor of an electrical line, the transferred charge is up to 0.6 C for buildings with metal façades. If the building is additionally equipped with a metal roof, the charge is reduced to less than 0.1 C. For (large) industrial buildings with steel reinforcement in the roof and in the ceilings, the charge is also very low, typically less than 0.1 C. In contrast, for houses without shielding elements such as metal façade, metal roof or reinforced concrete ceiling, the charge is relatively high, in the range of several coulombs. These results were obtained using copper or aluminum as materials for the external LPS. The use of normal steel increases the charge slightly. On the other hand, the use of stainless steel increases the charge to a higher extent due to the poor conductivity of stainless steel.