Barbados Wireman Licence Exam flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's law

The current through a conductor is directly proportional to voltage and inversely proportional to resistance: V = I × R, where V is volts, I is amperes, and R is ohms.

Electrical power formula

Power in a DC circuit equals voltage multiplied by current: P = V × I. It can also be expressed as P = I²R or P = V²/R, giving watts when using volts and amperes.

Series circuit

A circuit with a single path for current. The current is the same through all components, the total resistance is the sum of individual resistances, and voltage divides in proportion to resistance.

Parallel circuit

A circuit with multiple current paths. The voltage across each branch is the same, the total current is the sum of branch currents, and total resistance is less than the smallest branch resistance.

Three-phase power

In a balanced three-phase system, total power equals √3 times line voltage times line current times power factor: P = √3 × V_L × I_L × cos φ, with V_L in volts and I_L in amperes.

Conductor resistance formula

The resistance of a conductor is R = ρL/A, where ρ is resistivity in ohm-metres, L is length in metres, and A is cross-sectional area in square metres. Resistance increases with length and decreases with area.

RMS value

For a sinusoidal alternating current, the root-mean-square value equals the peak value divided by √2, approximately 0.707 times the peak. It represents the equivalent heating effect of direct current.

Power factor

Power factor is the cosine of the phase angle between voltage and current in an AC circuit, equal to resistance divided by impedance (cos φ = R/Z). It indicates how effectively power is used.

Overload protection

A protective device must operate before the conductor exceeds its safe current-carrying capacity. The device rating (In) must not exceed the cable capacity (Iz) after applying derating factors for temperature, grouping, and installation method.

Voltage drop limits

BS 7671 requires voltage drop from the origin of the installation not to exceed 3% for lighting circuits and 5% for other circuits, based on the declared supply voltage.

RCD requirement for sockets

Socket-outlet circuits rated up to 32 A generally require 30 mA RCD protection for additional protection against electric shock, unless the installation is under supervision of a skilled person.

CPC sizing rule

For phase conductors up to 16 mm², the circuit protective conductor must be the same cross-sectional area. Above 16 mm², a reduced size may be used if the CPC is at least half the phase conductor size.

Isolation and switching

A means of isolation must break all live conductors, including the neutral if it is not reliably at earth potential. Switching may be in the line conductor only if the neutral is earthed.

Cable bending radius

Cables must not be bent tighter than the manufacturer's minimum bending radius, typically four times the overall cable diameter for fixed wiring, to prevent damage to insulation and conductors.

Safe zones for cables

Cables buried in walls must be run within 150 mm of the ceiling, within 150 mm of a corner, or horizontally/vertically aligned with a socket or switch, or protected by earthed conduit.

Termination of conductors

Conductors must be terminated in compatible terminals with all strands intact. No strands may be cut off to fit a terminal, as this reduces current-carrying capacity and increases resistance.

Cable support spacing

Cables must be supported at intervals that prevent strain, typically every 300–400 mm for horizontal runs, and closer where cables are vertical or subject to vibration.

Harmonised colour coding

In harmonised cable, line conductors are brown, neutral is blue, and the protective earth conductor is green/yellow. These colours must be used consistently throughout the installation.

Earthing system types

TN-S has separate neutral and earth from the supply; TN-C-S combines neutral and earth in the supply; TT has a local earth electrode; IT has an isolated supply or high impedance earth.

Earth fault loop impedance

The total impedance of the earth fault path must be low enough for the protective device to operate within the required disconnection time, typically 0.4 s for 230 V final circuits.

Maximum disconnection times

For TN systems, final circuits up to 32 A must disconnect within 0.4 s; TT systems within 0.2 s; distribution circuits within 5 s. These times ensure protection against indirect contact.

RCD types and ratings

30 mA RCDs provide additional protection against electric shock; 100 mA or 300 mA RCDs may be used for fire protection or selectivity. RCDs must be tested regularly.

Main protective bonding

Main protective bonding conductors connect extraneous conductive parts to the main earthing terminal. Minimum size is 6 mm² for TN-C-S, 10 mm² for TN-S, or half the supply neutral if smaller.

TT system protection

A TT system relies on a local earth electrode and therefore requires RCD protection because the earth fault loop impedance is too high for overcurrent protective devices to operate within the required time.

Insulation resistance test

Insulation resistance is measured with a 500 V DC tester between live conductors and earth. The minimum acceptable value is 1 MΩ for circuits up to 500 V, indicating healthy insulation.

Ring final circuit test

For a ring final circuit, the end-to-end resistance of line, neutral, and CPC should be measured and should be within 0.05 Ω of each other, confirming continuity and correct connections.

Polarity test

Polarity testing verifies that line conductors are connected to the centre pin of sockets, switches are in the line conductor, and no neutral is switched, ensuring safe operation.

RCD tripping time test

An RCD should trip within 300 ms at its rated residual current (IΔn) and within 40 ms at five times IΔn. These times confirm correct operation and speed of disconnection.

Electrical Installation Certificate

An EIC is issued for new installations, complete rewires, and major alterations. It records the design, construction, inspection, and test results, and confirms compliance with the wiring regulations.

Isolation and lock-off

Before work, isolate the supply, lock off the isolator, and prove dead with an approved voltage tester on all conductors. This prevents accidental re-energisation and electric shock.

Live working precautions

Live working is permitted only when it is unreasonable to work dead. A risk assessment, insulated tools, appropriate PPE, and a second person may be required to ensure safety.

Consumer unit location

The consumer unit must be installed in an accessible position, with its main switch clearly labelled and all circuits identified. Spare ways must be blanked to maintain IP rating.

Meter tails sizing

Meter tails must be sized according to the supply current, typically 25 mm² copper for a 100 A single-phase supply, and must be protected from mechanical damage and corrosion.