NVQ L4 Electrician cheat sheet

EAWR 1989 requires electrical systems to be constructed and maintained to prevent danger; work must be done by competent persons and, where practicable, with the system dead.

Hierarchy of control: eliminate the hazard, substitute safer equipment, use engineering controls, then administrative controls, with PPE as the last line.

Safe isolation sequence: identify the circuit, isolate all live conductors, lock and tag, prove the voltage indicator, test for dead on every conductor, then re-prove the indicator.

GS38 voltage detectors have fused leads, finger guards and limited exposed tips; they must be proved on a known source before and after testing for dead.

BS 7671 requires 30 mA additional protection for socket outlets up to 32 A and for mobile equipment up to 32 A used outdoors.

Arc flash risk increases with high prospective fault current and loose connections; isolation, remote operation and appropriate PPE reduce exposure.

Suspected asbestos in older switchgear, fuse boards or cable ducts must stop work until a survey confirms the material and controls are agreed.

WEEE, lamps containing mercury, batteries and contaminated cable must be segregated and consigned to authorised waste carriers with duty-of-care records.

Design current Ib must satisfy Ib ≤ In ≤ Iz, where In is the protective device rating and Iz is the installed cable current-carrying capacity after derating.

BS 7671 voltage drop limits for public low-voltage supplies are 3% for lighting and 5% for other circuits from the origin to the load.

Earth fault loop impedance Zs must be low enough for the protective device to disconnect within the required time; Zs = Ze + (R1+R2) for a radial circuit.

TN disconnection times are 0.4 s for final circuits up to 32 A and 5 s for distribution circuits; TT systems are 0.2 s and 1 s respectively.

Cable tabulated capacity It must be at least In divided by the product of applicable rating factors Ca, Cg, Ci and Cs.

Protective conductors must satisfy the adiabatic equation k²S² ≥ I²t, or be selected from the standard table where the fault current and time are known.

Diversity assessment must use manufacturer data or recognised guidance; it reduces maximum demand but must not overload any final circuit or distribution board.

A 30 mA RCD is required for socket outlets up to 32 A in dwellings and for mobile equipment up to 32 A used outdoors, unless the installation meets a stated exception.

Initial verification sequence: safe isolation, visual inspection, continuity of protective conductors, ring final continuity, insulation resistance, polarity, earth loop impedance, RCD tests and functional checks.

Insulation resistance is measured at 500 V DC for 230/400 V circuits with sensitive equipment disconnected; the minimum acceptable value is 1 MΩ.

Continuity of protective conductors is proved by a low-resistance test; main protective bonding must be confirmed at the origin and at extraneous conductive parts.

Polarity must be verified at every outlet; line must be connected to the centre contact of lampholders and protective conductors must not be switched.

Ze is measured with the supply isolated and the main earthing conductor disconnected; the value must be within the distributor's stated maximum or design assumptions.

A 30 mA RCD should not trip at half rated current, should trip at rated current within 300 ms and at five times rated current within 40 ms.

An EIC is issued for new installations, a MEIWC for minor works and an EICR for existing installations; each is supported by schedules of inspections and test results.

EICR observations are coded C1 danger present, C2 potentially dangerous, C3 improvement recommended and FI further investigation required.

Half-split testing divides a circuit into sections and tests at the midpoint; the result identifies which half contains the fault and reduces the number of tests.

Insulation resistance faults are located by isolating the circuit, disconnecting loads and testing line-neutral, line-earth and neutral-earth separately.

A neutral-earth insulation fault can cause RCD tripping even when the circuit is switched off; shared neutrals and damp accessories are common causes.

A broken ring final can overload one leg and cause high loop impedance at sockets; end-to-end r1, rn and r2 tests reveal the open conductor.

High-resistance joints show as voltage drop under load, local heating and intermittent operation; torque checks and thermal imaging confirm the defect.

Short-circuit faults are line-to-line or line-to-neutral; earth faults are line-to-earth; both require isolation and sectional insulation testing.

Motor faults are diagnosed by supply voltage, winding resistance balance, insulation resistance to earth and overload settings.

Intermittent faults are commonly caused by thermal cycling, vibration, loose terminals or moisture; load cycling and monitoring capture the condition when it occurs.

Planned preventive maintenance follows fixed intervals; condition-based maintenance acts on measured temperature, insulation resistance, vibration or partial discharge.

Thermal imaging compares phase temperatures under load; a hot joint, overloaded conductor or unbalanced phase indicates increased resistance or current.

Insulation resistance trending is more informative than a single pass value; a falling trend indicates moisture, contamination or thermal ageing.

Polarization index is the 10-minute insulation resistance divided by the 1-minute value; values below about 2 may indicate moisture or contamination in motor windings.

Earth loop impedance and RCD trip-time records should be compared with previous results to detect deterioration in protective earthing and devices.

Partial discharge in HV insulation can be detected by ultrasonic, acoustic or electrical sensors before breakdown; trend and phase location guide intervention.

A CMMS asset register should record location, rating, serial number, maintenance plan, work orders and test history for each item.

Battery and UPS maintenance includes terminal torque, electrolyte level where applicable, impedance or conductance tests and functional discharge checks.

A work breakdown structure decomposes the project into manageable packages; each package can be costed, scheduled and assigned to a competent supervisor.

The critical path is the longest dependent sequence through the network; float on non-critical activities can be used without delaying completion.

Resource levelling moves activities within float to reduce peak labour or plant demand; resource smoothing may extend duration.

Earned value compares planned value, earned value and actual cost; SPI = EV/PV and CPI = EV/AC.

RAMS and isolation schedules must be prepared before work starts, with permits, lock-off points and emergency arrangements agreed with the client.

Long-lead items such as switchgear, transformers and specialist cable should be identified early and tracked against the procurement schedule.

Commissioning plans define inspection, testing, energisation, performance checks, acceptance criteria and responsibilities before handover.

Handover documentation includes as-built drawings, test certificates, O&M manuals, training records and warranties.

The Health and Safety at Work etc. Act 1974 imposes general duties on employers and self-employed persons to protect workers and others affected by the work.

The Electricity at Work Regulations 1989 require electrical systems to be constructed and maintained to prevent danger; competence and safe systems of work are central.

BS 7671 is not a statute; compliance may be required by contract, and it is used as evidence of reasonable practice under health and safety law.

In England and Wales, notifiable electrical work in dwellings falls under Building Regulations Part P and is certified through a competent person scheme or building control.

CDM 2015 projects are notifiable to HSE when they exceed 30 working days with more than 20 workers simultaneously, or exceed 500 person-days.

Contracts such as JCT and NEC set out payment, variation, delay and dispute procedures; the contract documents determine the legal obligations.

Waste duty of care requires electrical waste to be stored safely, transferred only to authorised carriers and documented with waste transfer notes.

Public liability insurance covers injury or damage to third parties; professional indemnity covers design or specification errors.

LED efficacy is lumens per watt; specifying higher lm/W reduces energy use for the same illuminance and lowers internal heat gain.

Power factor is kW divided by kVA; low power factor increases current and losses, and power factor correction reduces reactive demand.

PV yield depends on irradiance, orientation, tilt, shading and inverter efficiency; MCS and BS EN 62446 define installation and verification practice.

Grid-connected PV and battery systems must meet DNO connection requirements; G98 applies to small generation and G99 to larger connections.

EV charging normally uses Mode 3; BS 7671 requires 30 mA RCD protection with Type A plus 6 mA DC detection or a Type B RCD.

Heat pump performance is expressed as COP at a condition and SCOP over a season; lower flow temperature improves efficiency.

Battery storage is specified by usable capacity, depth of discharge, round-trip efficiency and C-rate; these affect cost and available energy.

Sub-metering and energy monitoring identify base loads and peak demand; the data supports load shifting, diversity review and efficiency measures.