Voltage drop

The voltage lost along a cable as current flows through its resistance. It is Ohm's law working against you, growing with both load current and run length. BS 7671 limits how much of the supply voltage may be dropped in the installation's own wiring, so a long run can force a larger conductor than the current alone would need.

Where to look it up: BS 7671 Appendix 4.

Taught and practised in the Installation section.