What is the maximum earth resistivity in ohmmeters for an area to be exempt from lightning exposure?

The maximum earth resistivity that allows an area to be considered exempt from lightning exposure is 100 ohmmeters. This value is significant in the context of grounding systems, where effective grounding is essential to divert lightning energy safely into the ground. When the earth resistivity is at or below this threshold, it indicates that the soil can effectively conduct electrical current, thereby reducing the risk of lightning damage to structures and electronic systems.

Lightning typically seeks paths of least resistance, and high earth resistivity can result in poor grounding, which may fail to sufficiently dissipate lightning strikes. Grounding systems designed for lightning protection must ensure low resistance to minimize potential voltage rise during a strike.

Therefore, understanding and adhering to the 100 ohmmeters limit is critical for any low-voltage communication systems installer to prevent safety hazards and ensure compliance with relevant codes and standards.