Lightning arresters are designed to protect electrical equipment from lightning effects. Which items are protected according to typical protection schemes?

Lightning arresters are designed to protect electrical equipment from lightning effects. Which items are protected according to typical protection schemes?

• A. II only
• B. II and III only
• C. I and II only
• D. I, II, and IV

Answer: (D)

Lightning arresters work by diverting surge current to ground and clamping the voltage seen by equipment that is on the protected side of the installation. Because only equipment that lies within that protected boundary benefits from the arresters, the items chosen as protected are the ones that sit on the protection boundary and would be damaged by a lightning surge if not guarded. The typical protection scheme includes the main service equipment and the downstream gear that rely on the same surge-mitigation path, plus another protected item that shares the same boundary. An item that lies outside this protected boundary isn’t safeguarded by these arresters, so it isn’t counted among the protected loads. Therefore, the configuration that includes the two main protected elements and the additional protected device aligns with how protection schemes are intended to function, which is why that option is correct.

Lightning arresters work by diverting surge current to ground and clamping the voltage seen by equipment that is on the protected side of the installation. Because only equipment that lies within that protected boundary benefits from the arresters, the items chosen as protected are the ones that sit on the protection boundary and would be damaged by a lightning surge if not guarded. The typical protection scheme includes the main service equipment and the downstream gear that rely on the same surge-mitigation path, plus another protected item that shares the same boundary. An item that lies outside this protected boundary isn’t safeguarded by these arresters, so it isn’t counted among the protected loads. Therefore, the configuration that includes the two main protected elements and the additional protected device aligns with how protection schemes are intended to function, which is why that option is correct.