Electrical calculators (BS 7671)
Voltage drop, cable Iz, Zs, RCD, power factor, kVA, adiabatic CPC and Ohm’s law — UK revision aids aligned to BS 7671:2018+A2:2022 themes.
Voltage drop
mV/A/m × Ib × L ÷ 1000 — Reg 525 limits 3% lighting / 5% other (230 V).
Cable current capacity (Iz)
Reference method C copper PVC — apply Ca, Cg, Ci then check Ib ≤ Iz.
Maximum Zs (0.4 s)
Table 41.3 indicative max Zs for MCB Type B/C at 230 V — verify on-site with instrument.
RCD / fault current
Compare prospective fault current (mA) with IΔn — plus disconnection time reminder.
Power factor
kVA from voltage and current
Adiabatic CPC (s)
s = √(I²t) / k — k ≈115 copper PVC (verify Table 43.1).
Ohm’s law
Enter any two of V, I, R — the third is calculated.
Indicative values from BS 7671 tables — always verify with the current edition, manufacturer data and on-site tests. Not a certified design.