← BackUK · BS 7671 A4:2026

Voltage Drop

This is a worked example. Editable with the UK Electrical pack.

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Inputs

Circuit category
A
m
mV/A/m

User-supplied — read this from your own copy of BS 7671 Appendix 4. This app never reproduces the licensed table.

Result

✓ PASS
7.920 V3.443 %

Limit (other) 5% · Table 4Ab

Utilisation 69%

T3 calculator — verify this result against your own calculation before relying on it professionally.

Show working

V_d = (mV/A/m × I_b × L) / 1000

V_d = (18.00 × 20.00 × 22.00) / 1000 = 7.920 V

  • Design current I_b: 20.00 A
  • Circuit length L: 22.00 m
  • Tabulated mV/A/m: 18.00 mV/A/m
  • Voltage drop V_d: 7.920 V
  • Voltage drop, % of nominal: 7.920 / 230 × 100 = 3.443 %

Clause: Appendix 4 §6.4 (Table 4Ab) · BS7671:2018+A4:2026

Kernel 0.1.0 · Profile voltage-drop v0.1.0