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

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.