BS 7671:2018+A4:2026 Tools
BS 7671 Electrical Calculators
Online calculation tools for UK electrical inspectors. Calculate maximum earth fault loop impedance, minimum protective conductor sizes, voltage drop, and ring continuity.
BS 7671:2018+A4:2026 Tables 41.2, 41.3, 41.4 & Appendix 14
Max Zs Calculator (BS 7671)
Calculate maximum earth fault loop impedance (Zs) for Type B, C, D MCBs and fuses with 80% temperature correction rule.
BS 7671 Regulation 543.1.3 & Formula 543.1.3
Adiabatic Equation Calculator
Calculate minimum protective conductor size (S) or maximum fault duration (t) using S = √(I²t) / k.
BS 7671 Appendix 4 Section 6 & Table 4D1B-4L4B
Voltage Drop Calculator
Calculate cable voltage drop (mV/A/m) with conductor temperature correction factors for single and three-phase circuits.
BS 7671 Part 6 / Guidance Note 3 Section 2.7.5
Ring Final Circuit Continuity
Verify ring final circuit test results (r1, rn, r2), expected figure-of-8 reading (R1 + R2), and detect spurs or cross-connections.