Quick Reference
Essential BS 7671 tables, formulas, and key values — the data you need most, all in one place.
12
Categories
46
Reference Items
BS 7671
18th Edition
Free
Always
Key Formulas
3 sections · 9 items
Essential electrical formulas for BS 7671 design and verification calculations.
Zs Values
5 sections · 5 items
Maximum earth fault loop impedance values for MCBs and fuses from BS 7671 Tables 41.2–41.6.
Cable Capacities
3 sections · 3 items
Current-carrying capacities (Iz) for common cable types from BS 7671 Appendix 4.
Correction Factors
4 sections · 4 items
Correction factors for ambient temperature, grouping, thermal insulation, and semi-enclosed fuses.
Voltage Drop
4 sections · 4 items
Voltage drop limits, mV/A/m values, and calculation formula from BS 7671 Appendix 4.
Conductor Resistance
2 sections · 2 items
R1+R2 values at 20°C and temperature correction factors from BS 7671 Appendix I.
Earthing & Bonding
4 sections · 4 items
Earthing systems, main bonding conductor sizes, supplementary bonding, and the adiabatic equation.
Special Locations
4 sections · 4 items
Requirements for bathrooms, swimming pools, EV charging, and construction sites from BS 7671 Part 7.
IP Ratings
3 sections · 3 items
IP code digits for solid object and water ingress protection levels.
RCD Requirements
4 sections · 4 items
When RCDs are required, RCD types, trip times, and AFDD recommendations per BS 7671.
Disconnection Times
2 sections · 2 items
Maximum disconnection times for TN and TT systems from BS 7671 Table 41.1.
Insulation Resistance
2 sections · 2 items
Minimum insulation resistance values and test procedures from BS 7671 Table 61.
About This Reference
From BS 7671:2018+A2:2022
All values, tables, and formulas are sourced from the IET Wiring Regulations (BS 7671) 18th Edition with Amendment 2. Use alongside the full regulations for your specific installation.
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