Reference Tables
Quick reference tables from BS 7671:2018+A2:2022 (18th Edition)
Max Zs Tables
Maximum earth fault loop impedance values for MCBs and fuses with 80% testing limits
Cable Current Ratings
Current carrying capacity (Iz) for common cable types by installation method
Correction Factors
Derating factors for ambient temperature (Ca), grouping (Cg), and thermal insulation (Ci)
Voltage Drop Tables
mV/A/m values for calculating voltage drop in cable runs
BS 7671 Tables
Table 4D1BTable 4H1BTable 4J2B
Includes
CopperAluminiumSingle-phaseThree-phase
IP Ratings Guide
Ingress protection ratings explained with common applications
MCB Time-Current Curves
Type B, C, D MCB tripping characteristics and selection guide
Using These Tables
For Design
- • Use tabulated values (It) for calculations
- • Apply correction factors: Iz = It × Ca × Cg × Ci
- • Use Max Zs values from design tables
For Testing
- • Apply 80% rule to Max Zs when testing
- • Compare measured values against limits
- • Document table refs on test certificates