What is the minimum size of a down conductor for lightning protection? What is the individual resistance and combine resistance of electrode? What is the resistance of grounding network?
There are two (2) classes of material requirements found in NFPA 780, the Standard for the Installation of Lightning Protection Systems. Class I materials are required for structure less than 75-ft in height, and Class II Materials are required for buildings greater than 75-ft in height. The down conductor is properly listed in the standard as a “Main Conductor Cable”.
- Class I – Copper: Minimum Gauge is 2 AWG, with a minimum individual strand size of 17 AWG.
- Class II – Copper: Minimum Gauge is 00 AWG, with a minimum individual strand size of 17 AWG.
- Class I – Aluminum: Minimum Gauge is 0 AWG, with a minimum individual strand size of 14 AWG.
- Class II – Aluminum: Minimum Gauge is 0000 AWG, with a minimum individual strand size of 14 AWG.
The calculation for predicting the resistance-to-ground of a grounding electrode can be found by following this link:
Calculating an entire grounding network generally requires computer modeling software, particularly in complex soil conditions. E&S Grounding Solutions has the complete CDEGS software package and can assist with these calculations, if provided with site plans and soil resistivity data.
The Engineering Experts at E&S Grounding Solutions