Copper conductors used for lightning protection shall be of what minimum conductivity when annealed?

The minimum conductivity requirement for annealed copper conductors used in lightning protection systems is set at 95%. This standard ensures that the conductors have sufficient ability to carry electrical currents safely and efficiently during a lightning event, minimizing the risk of damage and providing effective protection. Annealed copper is specifically chosen for its ductility and increased conductivity after being subjected to a heat treatment process, enhancing its performance in high-stress situations typical with lightning strikes. By specifying 95% conductivity, industry standards aim for a level of electrical performance that substantially reduces the likelihood of failure or excessive resistance, which could lead to safety hazards.

The other options, while they denote varying levels of conductivity, do not meet the current industry standards for lightning protection systems. Conductors with lower conductivity percentages would not provide the necessary assurance of performance during a lightning surge, which is critical for both safety and system efficacy.