EWRB Electrical flashcards

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

Ohm's law

Current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance, written as V = I × R.

Three-phase power formula

For a balanced load, total real power equals √3 multiplied by line voltage, line current and power factor: P = √3 × V_L × I_L × cos φ.

Impedance formula

Impedance is the total opposition to alternating current and combines resistance with reactance: Z = √(R² + X²), measured in ohms.

Inductive reactance

The reactance of an inductor increases with frequency according to X_L = 2πfL, where f is in hertz and L is inductance in henrys.

Conductor resistance formula

Resistance equals resistivity times length divided by cross-sectional area, R = ρL/A; copper has a resistivity of about 1.72 × 10⁻⁸ Ω·m at 20 °C.

Power factor correction

The capacitive reactive power needed to raise power factor equals kW × (tan φ₁ − tan φ₂), where φ₁ is the existing and φ₂ the target phase angle.

MEN system

Multiple earthed neutral: the neutral is earthed at the transformer star point, at the installation point and at each separate structure, with neutral and earth kept separate downstream.

Voltage drop formula

Single-phase voltage drop equals 2 × I × L × R divided by 1000, with R in ohms per kilometre and L in metres; three-phase calculations use √3 instead of 2.

Prescribed electrical work

Work on electrical installations and equipment that the Electricity (Safety) Regulations 2010 require to be done by, or under the supervision of, a registered and licensed person.

High-risk prescribed electrical work

Categories such as mains work and connecting an installation to supply, which must be inspected and covered by an Electrical Safety Certificate issued by a registered electrical inspector.

Certification of prescribed electrical work

The document a registered worker issues on completion, declaring the work complies with the Wiring Rules and regulations, with copies retained for inspection.

Practising licence

The annual licence issued by the Electrical Workers Registration Board that legally entitles a registered person to carry out or supervise prescribed electrical work.

Live work justification

Live work is allowed only where de-energising would create greater risk, and only after a hazard assessment with approved test equipment and suitable personal protective equipment.

NZECP 34

The New Zealand Electrical Code of Practice for electrical safe distances, which sets minimum approach distances to overhead lines and requires the line owner's consent for closer work.

Supervision duty

A licensed supervisor must ensure the trainee's work is done competently and safely, remain accountable for it, and certify the completed prescribed electrical work.

Isolation verification

Prove the tester on a known live source, test the conductors to be worked on, then re-prove the tester; conductors stay live until proven otherwise.

AS/NZS 3000

The Wiring Rules, the joint Australian and New Zealand standard for designing and constructing electrical installations, given legal force in New Zealand by regulation.

AS/NZS 3008.1.1

The standard used to select cable size and to determine current-carrying capacity, voltage drop and short-circuit withstand for typical New Zealand installation conditions.

AS/NZS 3017

The standard for verification of electrical installations by inspection and testing, describing the required tests and acceptable results before connection to supply.

AS/NZS 3760

The standard for in-service safety inspection and testing of electrical equipment, forming the basis of the test-and-tag regime for appliances and flexible leads.

AS/NZS 3019

The standard for periodic verification of existing electrical installations, used to judge whether an installation remains safe and compliant throughout its service life.

AS/NZS 4836

The standard for safe working on low-voltage electrical installations and equipment, covering isolation, testing, protective equipment and emergency response procedures.

Harmonised conductor colours

New Zealand uses brown, black and grey for phase conductors, blue for neutral and green/yellow for earth; older installations use red, white and blue for phases.

AS/NZS 3112

The standard defining the New Zealand and Australian three-pin plug and socket outlet, including pin configuration, pin dimensions and insulation requirements.

Five safety rules

Isolate, secure against re-energisation, verify absence of voltage, earth and short-circuit where required, and protect or barricade adjacent live parts.

Prove-test-prove

Confirm the voltage tester works on a known live source, test the target conductors to prove they are dead, then re-prove the tester afterwards.

Insulation resistance test

Measure between conductors and between live conductors and earth at 500 V DC with loads disconnected; a 230/400 V installation should read at least 1 MΩ.

RCD trip time limit

A 30 mA residual current device must operate within 300 milliseconds at rated residual current, and within 40 milliseconds at five times rated residual current.

Polarity test

Confirms that switches and fuses are inserted in the phase conductor and that active, neutral and earth are connected to the correct socket outlet terminals.

Earth fault loop impedance

The total impedance of the path from a fault back to the supply transformer, measured to confirm the protective device will disconnect within the required time.

Lockout tagout

The isolating device is locked and fitted with a danger tag, with the key held by the worker so the circuit cannot be re-energised until work is complete.

Arc flash PPE

Arc-rated clothing, face protection and voltage-rated gloves worn when working near energised equipment, selected to suit the assessed incident energy level.