EWRB Electrical cheat sheet

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

Balanced three-phase power: P = √3 × V_L × I_L × cos φ, where V_L and I_L are line values.

Impedance: Z = √(R² + X²); inductive reactance X_L = 2πfL; capacitive reactance X_C = 1/(2πfC).

Conductor resistance: R = ρL/A; for copper ρ ≈ 1.72 × 10⁻⁸ Ω·m at 20 °C and the temperature coefficient α ≈ 0.00393 per °C.

Single-phase voltage drop: V_d = (2 × I × L × R_c)/1000 with R_c in Ω/km and L in metres; substitute √3 for the 2 in three-phase circuits.

New Zealand nominal supply values: 50 Hz, 230 V phase-to-neutral, 400 V phase-to-phase.

MEN system: neutral is earthed at the transformer star point, at the installation point, and at each separate structure fed by a submain; neutral and earth are separated downstream of each MEN link.

Cable current rating is derated by multiplying factors for ambient temperature, grouping, thermal insulation, burial depth and soil thermal resistivity.

Power factor correction: capacitive kVAR required = kW × (tan φ₁ − tan φ₂), where φ₁ is the existing and φ₂ the target angle.

Prescribed electrical work may only be done by a registered person holding a current practising licence, or by another person under that person's supervision.

High-risk prescribed work - including mains work and connecting an installation to supply - must be inspected and covered by an Electrical Safety Certificate issued by a registered electrical inspector.

On completion the worker issues a Certification of prescribed electrical work declaring compliance, and the certification and inspection records must be retained and produced on request.

A practising licence is renewed annually through the Electrical Workers Registration Board and depends on demonstrated current competence.

Work on live conductors is permitted only where de-energising would create greater risk, and only after a hazard assessment with approved test equipment and PPE.

Isolation must be verified with an approved voltage tester that is proved on a known source before and after the test; conductors are treated as live until proved dead.

NZECP 34 sets minimum safe distances from overhead lines and requires the line owner's written consent before working inside those distances.

Electrical equipment supplied in New Zealand must be shown to comply with an approved electrical safety standard, with the supplier responsible for that compliance.

AS/NZS 3000 (the Wiring Rules) is the governing installation standard and is given legal effect in New Zealand by the Electricity (Safety) Regulations 2010.

AS/NZS 3008.1.1 is used to select cable size and to obtain current-carrying capacity, voltage drop and short-circuit ratings for typical installation conditions.

AS/NZS 3017 specifies verification by inspection and testing before an installation is connected to supply.

AS/NZS 3019 covers periodic verification of existing installations; AS/NZS 3760 covers in-service inspection and testing (test and tag) of electrical equipment.

AS/NZS 4836 sets safe working practices for low-voltage work; AS/NZS 3012 sets additional requirements for construction and demolition sites.

Harmonised conductor colours are brown, black and grey for phases, blue for neutral and green/yellow for earth; older installations use red, white and blue for phases.

AS/NZS 3112 defines the New Zealand/Australian three-pin plug and socket outlet configuration, pin dimensions and insulation requirements.

Certification documents form a chain: Certification of prescribed electrical work from the worker, Electrical Safety Certificate from the inspector, and Records of Inspection retained for audit.

The five safety rules: isolate, secure against re-energisation, verify absence of voltage, earth and short-circuit where required, and protect adjacent live parts.

Test sequence for verification: visual inspection, continuity of protective earthing and bonding, insulation resistance, polarity, earth fault loop impedance, RCD operation, then functional tests.

Insulation resistance is measured at 500 V DC with loads and sensitive electronics disconnected; the minimum acceptable value for a 230/400 V installation is 1 MΩ.

A 30 mA RCD must operate within 300 ms at its rated residual current, and within 40 ms when tested at five times rated residual current.

Earth fault loop impedance is measured to confirm the protective device will disconnect the fault within the time required by AS/NZS 3000.

Polarity testing confirms that switches and fuses are inserted in the phase conductor and that socket outlet terminals are correctly connected.

Lockout/tagout: the isolating device is locked, a danger tag fitted, and the key retained by the worker until the work is finished and the circuit is formally restored.

PPE for work near energised equipment includes voltage-rated gloves, insulated tools and arc-rated clothing selected for the assessed incident energy.