Barbados Wireman Licence Exam cheat sheet

Ohm's law: V = I × R; power: P = V × I = I²R = V²/R.

In a series circuit, current is constant; voltage divides in proportion to resistance.

In a parallel circuit, voltage is constant; current divides inversely with resistance.

Three-phase power (balanced): P = √3 × V_L × I_L × cos φ.

Conductor resistance: R = ρL/A; ρ is resistivity (Ω·m), L length (m), A cross-sectional area (m²).

AC impedance: Z = √(R² + X²); power factor = cos φ = R/Z.

Energy (kWh) = power (kW) × time (h); 1 kWh = 3.6 MJ.

For a sine wave, RMS = peak / √2 ≈ 0.707 × peak; average = 0.637 × peak.

Final circuits must be protected against overload and short circuit; protective device rating must not exceed conductor current-carrying capacity.

Socket-outlet circuits require 30 mA RCD protection where required by the applicable code (e.g., BS 7671).

Cable current-carrying capacity must be derated for ambient temperature, grouping, and thermal insulation.

Minimum cross-sectional area for lighting circuits is typically 1.0 mm² or 1.5 mm² copper, depending on code.

Earth continuity conductor sizing: for phase conductors ≤ 16 mm², the CPC is typically the same size; above 16 mm², a reduced size may be permitted.

Isolation and switching must break all live conductors; a neutral need not be switched if it is reliably at earth potential.

Voltage drop limits: typically 3% for lighting and 5% for other uses from the origin of the installation.

Every installation must have a means of isolation and a main protective device; discrimination between devices must be ensured.

Cable bends must not be tighter than the manufacturer's minimum bending radius (often 4× cable diameter for fixed wiring).

Cables in walls must be run in safe zones (horizontal within 150 mm of ceiling, vertical within 150 mm of corners) or protected by earthed conduit.

Conductors must be terminated with compatible terminals; no strands may be cut away to fit a terminal.

Jointing is permitted only in accessible, enclosed, and approved enclosures; no joints in conduit runs without access.

Cable supports must be at intervals that prevent strain; typical maximum spacing is 300–400 mm for horizontal runs.

All exposed conductive parts must be bonded to the protective earth; bonding conductors must be continuous and mechanically protected.

Enclosures must maintain their IP rating after cable entry; unused openings must be sealed.

Colour coding: line conductors brown, neutral blue, protective earth green/yellow (harmonised).

Earthing system types: TN-S, TN-C-S, TT, IT; the type determines the protective device and RCD requirements.

Earth fault loop impedance Zs must be low enough to operate the protective device within the disconnection time (e.g., 0.4 s for 230 V final circuits).

Maximum disconnection times: 0.4 s for TN systems ≤ 32 A final circuits; 0.2 s for TT systems; 5 s for distribution circuits.

RCDs: 30 mA for additional protection; 100 mA or 300 mA for fire protection or selectivity.

Main protective bonding conductor size: ≥ 6 mm² for TN-C-S, ≥ 10 mm² for TN-S, or half the supply neutral if smaller.

Supplementary bonding resistance between exposed and extraneous conductive parts must be ≤ 0.05 Ω (or ≤ 0.1 Ω in some codes).

TT systems require an RCD because the earth fault loop impedance is too high for overcurrent devices.

Surge protective devices (SPDs) must be installed where required by the code and coordinated with the earthing system.

Test sequence: visual inspection, continuity of protective conductors, continuity of ring final circuit conductors, insulation resistance, polarity, earth fault loop impedance, RCD operation, functional tests.

Insulation resistance test voltage: 500 V DC for circuits ≤ 500 V; minimum acceptable value 1 MΩ (some codes require ≥ 1 MΩ).

Continuity of CPC: resistance should be low and consistent with conductor length and size; typical values < 1 Ω for short runs.

Ring final circuit continuity: end-to-end resistance of line, neutral, and CPC should be within 0.05 Ω of each other.

Polarity test: verify that line is connected to the centre pin of sockets and that switches are in the line conductor.

Earth fault loop impedance test: measured Zs must be ≤ the tabulated maximum for the protective device and disconnection time.

RCD test: verify tripping time at IΔn and 5×IΔn; typical maximum times are 300 ms and 40 ms respectively.

Certification: Electrical Installation Certificate (EIC) for new work; Minor Works Certificate for small alterations; Periodic Inspection Report for existing installations.

Before work, isolate and lock off; prove dead with an approved voltage tester on all conductors.

Use of portable electrical equipment requires regular inspection and testing; Class I earthed, Class II double insulated.

Live working is permitted only when it is unreasonable to work dead and suitable precautions are taken (risk assessment, insulated tools, PPE).

First aid for electric shock: do not touch the casualty until isolated; call emergency services; commence CPR if trained.

Arc flash risk: maintain safe approach distances; use appropriate PPE (arc-rated clothing, face shield) for live work.

Safety signs: yellow triangle for warning, blue circle for mandatory action, red circle for prohibition.

Working at height: use ladders only for short-duration light work; scaffold or platform for longer tasks.

Report all electrical incidents and near misses; keep records of maintenance and testing.

Consumer unit must be located in an accessible position; main switch must be clearly labelled.

Service head: supply authority's responsibility up to the meter; consumer's responsibility from meter onward.

Main protective device rating must be coordinated with the supply capacity and consumer unit busbar rating.

Meter tails must be sized according to supply current; typical 25 mm² for 100 A supply.

Earthing conductor from consumer unit to earth electrode must be protected against mechanical damage and corrosion.

Consumer unit requires a main switch, RCDs/RCBOs, and MCBs for final circuits; spare ways should be blanked.

Isolation of supply: main switch must disconnect all live conductors; a means of isolation for maintenance must be provided.

Labelling: each circuit must be identified; RCD test notice and earthing arrangement label must be present.