Abstrak
This study aimed to evaluate the external lightning protection system installed at the Regional Library Building of Tarakan City using the Mesh and Rolling Sphere Methods in accordance with PUIPP and SNI 03-7015-2004 standards. The evaluation was conducted to ensure the level of protection of the building against lightning strikes and the suitability of the grounding resistance value to applicable standards. A descriptive quantitative method was employed, with field data collected on building dimensions, thunderstorm day frequency, and grounding resistance measured using an Earth Meter. The calculation results indicated that the protected area covered 2,327.01 m², with a direct lightning strike frequency of 3.09 times per year and a Level II protection classification with an efficiency of 0.96. The ground resistance value obtained from field measurements was 0.488 Ω, while the value calculated based on SNI standards was 0.1426 Ω. Furthermore, analysis using the rolling sphere method showed that a sphere radius of 30 meters with a lightning current of 93.21 kA did not make contact with any part of the building, indicating that the external lightning protection system was functioning properly. Based on the analysis, the lightning protection system of the building complied with safety standards and operated effectively; nevertheless, periodic inspections were recommended to ensure sustained optimal system performance.