Electrical Theory and Fundamentals for the Barbados Wireman Licence
Core concepts
You must be comfortable with Ohm's law (V = I × R), the power relationships (P = V × I, P = I²R, P = V²/R), and how they combine in single-phase and three-phase circuits. Know the difference between a.c. and d.c., the meaning of r.m.s. values, frequency (Barbados supply is 50 Hz), and why power factor matters: true power in watts, apparent power in volt-amperes, and reactive power in VARs. Understand series and parallel resistance rules, voltage drop in conductors, and the relationship between conductor resistance, length, cross-sectional area and temperature. Basic magnetism, induction, and transformer action underpin motors and protective devices, so revise those too.
Traps to watch
Questions often mix units (kW versus kVA), give a three-phase load and expect the √3 factor, or quote a power factor below unity and ask for current rather than power. Another common trap is confusing nominal voltage with measured voltage under load, or forgetting that resistance rises with temperature in metallic conductors. Read whether the question asks for total or per-phase values.
Worked example
A 230 V single-phase motor draws 10 A at a power factor of 0.8. True power = 230 × 10 × 0.8 = 1840 W (1.84 kW). Apparent power = 230 × 10 = 2300 VA. The difference (460 VAR) is reactive. If asked for current from kW, always divide by power factor: I = P / (V × pf).
Rule of thumb
For quick three-phase estimates, current ≈ kVA × 1000 / (√3 × line voltage). At 400 V, that is roughly 1.44 A per kVA.