Cable Voltage Drop
BS 7671 voltage drop check + Vd %
A
Reading 20 A
m
Reading 25 m
Results
Voltage drop
9V
Vd %
3.91%
BS 7671 limit5% (11.5 V)
Result✓ Within limit
mV/A/m used18 (2.5 mm² T&E, single-phase)
Cable length25 m
Suggested Materials
2.5mm² Twin & Earth cable (6242Y)
Inc. 10% slack
28 m
20A junction box
1 pc
32A 30mA RCBO (or as required by circuit)
1 pc
Estimates use standard UK trade rules of thumb. Always check the bag/spec on the day.