Wiring Methods, Conductors, and Terminations
What the candidate must know
Candidates must select conductors by current-carrying capacity, voltage drop, and environmental suitability, and choose wiring methods to match: conduit, trunking, tray, armoured cable, and flexible cord. Know the correction factors that derate a cable: ambient temperature, grouping, thermal insulation, and enclosure. Understand terminations: crimped lugs, screw terminals, spring terminals, and the tools and torque each requires. Recognise the purpose of ferrules on stranded conductors, glanding and strain relief, and the difference between a mechanical and a soldered joint.
Traps that appear in questions
- Using the tabulated current rating without applying correction factors.
- Mixing conductor classes; fine-stranded cable in a screw terminal without a ferrule can spread and loosen.
- Ignoring voltage drop on long runs; a cable can be thermally adequate yet fail on drop.
- Omitting strain relief or glanding so the termination carries mechanical load.
- Assuming a larger cable always solves a problem when the fault loop impedance or termination capacity becomes the limit.
Worked example / rule of thumb
A 30 m run carrying 20 A on a 4 mm² copper conductor has a resistance around 7.4 mΩ per metre per conductor, giving roughly 4.4 V drop on the round trip at 20 A, about 1.9 percent of 230 V. That passes a 3 percent limit. Rule of thumb: check thermal capacity first, then voltage drop, then fault loop impedance, then termination capacity; the smallest of these governs the choice.