What key factors determine earth bonding conductor sizing, and how do specifications differ by earthing system and installation type?

Q: What key factors determine earth bonding conductor sizing, and how do specifications differ by earthing system and installation type?A: Earth bonding cable sizing adheres to BS7671 regulatory frameworks, which categorize requirements based on earthing system type (TN-S, TN-C-S, TT, etc.), conductor material, and environmental protection. For TN-S and TN-C-S systems, copper equivalent cross-sections range from 4mm² to 70mm² for line/neutral conductors, with corresponding earth conductors scaling from 6mm² to 35mm² depending on burial status and corrosion resistance needs.   Critical distinctions include: buried unprotected conductors requiring minimum 25mm² copper (or 50mm² steel) versus 16mm² for corrosion-protected variants; main bonding conductors mandating at least 50% of the earthing conductor size (minimum 6mm²); and PME supply configurations specifying 10mm² minimum bonding conductors regardless of line size. Material restrictions prohibit aluminum or copper-clad alternatives without specialized safeguards, while conductors ≤10mm² must utilize solid copper to ensure conductivity and mechanical integrity under fault conditions.   Installation context further modifies requirements: unburied unprotected conductors demand 4mm² minimum, while dual-protected (corrosion and mechanical) installations allow 2.5mm². These specifications balance fault current handling capacity with environmental durability, ensuring system safety across residential, commercial, and industrial applications.