A lightning arrester, also known as a surge arrester, is a device that protects electrical systems and equipment from lightning strikes and electrical surges. It is compulsory on buildings for several reasons: 1. _Protects against lightning strikes_: Lightning arresters absorb and divert lightning strikes, preventing damage to electrical systems, equipment, and the building structure. 2. _Reduces risk of fire_: Lightning strikes can cause electrical fires, which can spread quickly. Lightning arresters help prevent these fires from occurring. 3. _Prevents electrical shock_: Lightning arresters ensure that electrical currents do not flow through the building's electrical system, reducing the risk of electrical shock to people and animals. 4. _Protects electrical equipment_: Lightning arresters safeguard electrical equipment, such as transformers, switchgear, and distribution panels, from damage caused by lightning strikes and electrical surges. 5. _Ensures continuity of electrical supply_: By protecting against electrical surges and lightning strikes, lightning arresters help ensure that the electrical supply remains continuous and reliable. 6. _Meets electrical codes and standards_: Installing lightning arresters is mandatory in many countries, as it meets electrical codes and standards, such as the National Electrical Code (NEC) and the International Electrotechnical Commission (IEC) standards. 7. _Reduces risk of damage to building structure_: Lightning strikes can cause significant damage to a building's structure, including roofs, walls, and foundations. Lightning arresters help prevent this damage. 8. _Protects people and assets_: Lightning arresters help protect people, assets, and equipment from the risks associated with lightning strikes and electrical surges. In summary, lightning arresters are compulsory on buildings to ensure protection against lightning strikes, reduce the risk of fire and electrical shock, protect electrical equipment, ensure continuity of electrical supply, meet electrical codes and standards, reduce damage to the building structure, and protect people and assets.