HSC Electrotechnology (VET) cheat sheet

Ohm's law: V = I × R; power P = V × I = I²R = V²/R. In a series circuit current is common and voltages add; in a parallel circuit voltage is common and currents add.

Electrical units: voltage in volts (V), current in amperes (A), resistance in ohms (Ω), power in watts (W), energy in joules (J) or kilowatt-hours (kWh); 1 kWh = 3.6 MJ.

Resistors in series add directly (RT = R1 + R2 + …); for parallel resistors 1/RT = 1/R1 + 1/R2 + …, and two in parallel give RT = (R1 × R2)/(R1 + R2).

Kirchhoff's laws: the sum of currents at a node is zero (current law) and the sum of voltages around a closed loop is zero (voltage law).

AC quantities: frequency f = 1/T; RMS value of a sine wave = peak ÷ √2 (≈0.707 × peak); peak = RMS × 1.414.

Conductor resistance: R = ρL/A, so resistance rises with length and resistivity and falls with cross-sectional area; temperature rise increases resistance of copper.

Power factor: true power P = V × I × cos φ; apparent power S = V × I in volt-amperes; reactive power Q = V × I × sin φ.

Instrument use: a voltmeter connects in parallel across the load, an ammeter in series with the load, and an ohmmeter only on a de-energised, isolated circuit.

WHS hierarchy of control ranks elimination, substitution, engineering controls, administrative controls and PPE, in that order of preference.

Before work, isolate the supply, lock and tag the isolation point, test for dead with a proven tester, and prove the tester on a known live source before and after.

The wiring rules (AS/NZS 3000) require protection against direct contact (insulation, barriers, enclosures) and indirect contact (earthing plus RCD or automatic disconnection).

Residual current devices: 30 mA RCDs are used for socket-outlet and personal protection circuits; a 300 mA device is for fire protection of equipment.

Electric shock severity depends on current through the body, path, duration and frequency; roughly 30 mA can cause muscular paralysis and 50 mA or more can be lethal.

Fire classes: A = solid combustibles, B = flammable liquids, C = flammable gases, E = electrical, F = cooking oils; water must never be used on live electrical fires.

First aid for electric shock: isolate the supply before touching the casualty, call emergency services, then apply DRABCD and treat burns.

Lock-out tag-out records identify the person, date and circuit; only the person who applied the lock removes it, or a documented procedure applies.

Cable current-carrying capacity depends on conductor size, insulation rating, installation method (enclosed, clipped, buried, in conduit), ambient temperature and grouping.

Voltage drop in a circuit is calculated from Vd = (2 × L × I × ρ)/A for single-phase two-wire circuits, where L is one-way length in metres.

Final subcircuit protection: the protective device rating must not exceed the cable's current-carrying capacity, and the circuit must satisfy both voltage drop and fault-loop impedance limits.

Cable colour code for single-phase a.c.: active brown, neutral blue, earth green/yellow; three-phase actives are brown, black and grey with blue neutral.

Standard socket-outlet circuits in domestic installations are typically 10 A or 16 A; lighting circuits are commonly protected at 10 A with 1.0 mm² or 1.5 mm² cable.

Maximum demand is estimated by diversity factors applied to connected load, not by simple addition of every appliance rating.

Earthing and bonding: the main earthing conductor connects the installation to the earth electrode; equipotential bonding ties metallic services to the earthing system.

Testing sequence for a new installation includes continuity of protective conductors, insulation resistance (≥1 MΩ at 500 V d.c.), polarity, and earth fault-loop impedance.

A transformer changes voltage by the turns ratio: Vs/Vp = Ns/Np; power in equals power out for an ideal transformer, so current ratio is inverse to the voltage ratio.

Three-phase supply: line voltage VL = √3 × phase voltage Vph for a star connection; line current IL = √3 × phase current Iph for a delta connection.

Single-phase induction motors are not self-starting; capacitor-start, capacitor-run or shaded-pole arrangements provide the rotating field.

A contactor is a remotely operated switch for load circuits; an overload relay protects the motor, while the contactor coil is controlled by pushbuttons or a PLC output.

DOL starting draws about 6–8 times full-load current; star-delta starting reduces starting current and torque to one third of DOL values.

A diode conducts in forward bias and blocks in reverse; a bridge rectifier converts a.c. to pulsating d.c. using four diodes.

A bipolar transistor is a current-controlled device (base current controls collector current, IC = βIB); a MOSFET is voltage-controlled at the gate.

Electrical drawings: a schematic shows electrical function without physical layout; a wiring diagram shows physical connections; a ladder diagram is used for control logic.

Work health and safety duties under the model WHS Act: the person conducting a business or undertaking must ensure health and safety so far as reasonably practicable.

A Safe Work Method Statement (SWMS) is required for high-risk construction work, including work near energised electrical installations.

Risk assessment steps: identify the hazard, assess the likelihood and consequence, control the risk using the hierarchy, then monitor and review.

A confined space is an enclosed or partially enclosed space not designed for continuous occupancy; entry requires a permit, atmospheric testing and a standby person.

Working at heights above two metres requires fall prevention such as guardrails, scaffolds or a harness anchored to a rated point.

Manual handling risk is reduced by mechanical aids, team lifting and load reduction; the worker must follow the PCBU's safe system of work.

Incident reporting: notifiable incidents include death, serious injury and dangerous incidents; the regulator must be notified immediately by phone.

Environmental controls for electrotechnology work include correct disposal of lamps containing mercury, batteries, refrigerant and e-waste under state regulations.

Batteries: capacity in ampere-hours (Ah); energy in watt-hours = Ah × nominal voltage; series cells add voltage, parallel cells add capacity.

Lead-acid cells have a nominal 2 V per cell, so a 12 V battery has six cells in series; charging requires a voltage above the nominal terminal voltage.

A relay uses a small coil current to switch a larger isolated load; a normally open contact closes when the coil is energised.

Thermal overload protection uses a bimetallic strip that bends with heat; it protects against sustained overcurrent, not short circuits (fuses or MCBs do that).

A miniature circuit breaker (MCB) trips on overcurrent via thermal (overload) and magnetic (short-circuit) elements; a fuse melts a calibrated element.

Cable and conductor selection considers current rating, voltage drop, mechanical strength, insulation temperature rating and environmental conditions.

Terminations must be mechanically and electrically sound: use correct lug or terminal type, correct torque, and no exposed conductor at the terminal.

Tagging and testing of portable electrical equipment follows AS/NZS 3760 with intervals set by the equipment type and environment of use.

A PLC scan cycle repeats: read inputs, execute the program logic, update outputs, then perform housekeeping.

Ladder logic symbols: normally open contact passes power when the bit is true; normally closed contact passes power when the bit is false; the coil writes the output bit.

Digital sensors: a proximity sensor detects metal without contact; a photoelectric sensor uses a light beam; a limit switch is actuated by mechanical contact.

Motor control interlocking prevents conflicting operations, for example forward and reverse contactors are interlocked so both cannot energise together.

Emergency stop circuits must be hard-wired and fail-safe; the stop function must override all other controls and require a deliberate reset.

Instrument accuracy: accuracy is the closeness to the true value, precision is repeatability; a class 1.0 meter has an error within 1% of full scale.

A multimeter on the wrong range or function can be damaged or cause a hazard; select the function and range before connecting to a live circuit.

Data and control cabling should be separated from power cabling to reduce electromagnetic interference; shielded cable is earthed at one end only.

Workplace communication: job documentation includes drawings, specifications, schedules, test results and commissioning records; each must be completed accurately and legibly.

A job safety analysis (JSA) breaks a task into steps and identifies hazards and controls for each step before work begins.

Quality assurance in electrotechnology relies on inspection and test plans, calibrated test instruments and documented results against acceptance criteria.

Team roles: a licensed electrician supervises and certifies electrical work; an apprentice must work under supervision and within their competence.

Customer service: confirm the scope with the client, explain the work and test results, and record any defects found and actions taken.

Continuous improvement uses feedback, incident reviews and audits to update procedures; records must be retained per the organisation's requirements.

Sustainable practice: select energy-efficient equipment, size conductors correctly to reduce losses, and use load control and power-factor correction.

Estimating: material cost plus labour hours at the applicable rate plus overhead and margin gives the quoted price; variations must be documented.

Protection against electric shock uses automatic disconnection of supply: the earth fault-loop impedance must be low enough that the protective device operates within the required disconnection time.

Circuit protection types: fuses and MCBs for overcurrent, RCDs for earth leakage, surge protective devices for transient overvoltages.

Insulation resistance testing uses a 500 V d.c. insulation tester with the supply isolated and loads disconnected; the minimum acceptable value is 1 MΩ.

Continuity testing verifies protective earthing and bonding conductors and the correct polarity of connections.

Earth electrode resistance is measured with an earth tester; a lower resistance is achieved with deeper or multiple electrodes and soil moisture.

Cable derating factors multiply the tabulated current-carrying capacity: ambient temperature, grouping, thermal insulation and installation method all reduce it.

Fault types: a short circuit is a low-resistance path between live conductors; an earth fault is a path from a live conductor to earth.

Switchboards must be accessible, labelled with circuit identification, and have the main switch and RCDs clearly identified.

Electrical energy and cost: energy (kWh) = power (kW) × time (h); cost = energy × tariff rate per kWh.

A wattmeter or energy meter measures true power; a clamp meter measures current without breaking the circuit and must be clamped around one conductor only.

Oscilloscopes display voltage against time; period is measured between successive identical points and frequency f = 1/T.

A signal generator provides test waveforms; the function (sine, square, triangle) and amplitude are set before connection to the circuit.

A variable autotransformer provides an adjustable a.c. voltage from a fixed supply; it does not provide isolation unless it is an isolating type.

Soldering: heat the joint and apply solder to the joint, not the iron tip; a good joint is shiny and concave, a cold joint is dull and grainy.

Cable termination: strip only the required length of insulation, avoid nicking the conductor, and use the correct crimp tool for the lug size.

Electrical hand tools: insulated tools are rated for live work only if marked with the voltage rating; a torque screwdriver ensures correct terminal torque.

Three-phase power: P = √3 × VL × IL × cos φ for a balanced load; total power is the sum of the phase powers.

Star (Y) connection: phase voltage = line voltage ÷ √3; phase current = line current. Delta connection: phase voltage = line voltage; phase current = line current ÷ √3.

Phase rotation determines motor direction; swapping any two of the three supply lines reverses the rotation.

A three-phase motor nameplate gives voltage, frequency, full-load current, power factor, efficiency and connection (star or delta).

Motor protection: overload relays are set to the motor full-load current; short-circuit protection is provided by fuses or a motor circuit breaker.

Power factor correction capacitors reduce the reactive current drawn from the supply; they are connected in parallel with the load and switched with it.

Cable sizing for three-phase circuits uses voltage drop Vd = (√3 × L × I × ρ)/A for a three-phase three-wire circuit.

Harmonics from non-linear loads such as variable-speed drives can overheat neutrals; the neutral current can exceed the phase current in some installations.

Renewable systems: a grid-connected solar PV array uses an inverter to convert d.c. to a.c. synchronised with the supply; an anti-islanding function disconnects on loss of grid.

Battery storage systems require a battery management system to balance cells and prevent overcharge, over-discharge and overheating.

Standards and compliance: electrical work must comply with AS/NZS 3000 and relevant product standards; non-compliant equipment must not be installed.

Certification: a Certificate of Electrical Safety or equivalent compliance certificate is issued for electrical work by the licensed person responsible.

Documentation for a completed job includes as-installed drawings, test results, equipment manuals, and operating instructions for the client.

Testing before energising: visual inspection, then continuity, insulation resistance, polarity, and where required earth fault-loop impedance and RCD trip time.

Fault finding follows a logical sequence: gather information, verify the symptom, isolate, test sections, identify the faulty component, repair and retest.

Records of test instruments must show current calibration; an out-of-calibration instrument invalidates the test results.

A capacitor stores charge Q = C × V; in a d.c. circuit it blocks steady current after charging; in an a.c. circuit its reactance XC = 1/(2πfC) falls as frequency rises.

An inductor opposes change in current; its reactance XL = 2πfL rises with frequency; in a d.c. circuit it behaves as a short circuit once the current is steady.

Impedance in an RLC circuit: Z = √(R² + (XL − XC)²); resonance occurs when XL = XC and the impedance is minimum (series) or maximum (parallel).

RC time constant τ = R × C; the capacitor charges to about 63% of supply voltage in one time constant and is effectively charged after five.

A diode's forward voltage drop is about 0.7 V for silicon; a zener diode regulates voltage when reverse-biased beyond its breakdown voltage.

A relay coil is an inductor; a freewheeling diode across the coil suppresses the voltage spike when the coil is de-energised.

A thermistor's resistance changes with temperature; an NTC thermistor's resistance falls as temperature rises and is used for temperature sensing.

A photodiode or LDR changes its conduction with light level; an optocoupler provides electrical isolation between control and power circuits.

Reading a drawing: the title block gives the project, drawing number, scale, revision and date; the revision table shows changes.

Electrical symbols: a circle with a cross is a lamp, a rectangle with a diagonal is a resistor, a capacitor is two parallel lines, and an earth symbol is three decreasing horizontal lines.

A single-line diagram shows the distribution from the supply authority through the main switchboard to subcircuits, with cable sizes and protection ratings.

A cable schedule lists each circuit's cable type, size, length, route and termination points; it supports material take-off and installation.

Scale: a drawing at 1:100 means one unit on the drawing represents 100 units in reality; dimensions on the drawing take precedence over scaled measurement.

Circuit identification: circuits are numbered and labelled at the switchboard; each circuit's protective device rating and cable size must match the schedule.

As-built drawings reflect the actual installation; they must be updated when changes are made so future maintenance is accurate.

Isolation points must be shown on drawings so maintenance personnel can locate the correct isolating device.

Personal protective equipment for electrical work includes insulated gloves rated for the voltage, face shield, arc-rated clothing and safety footwear.

Test before touch: prove the tester on a known source, test the circuit, and re-prove the tester after testing to confirm it still works.

Live work is permitted only when it is unreasonable for the equipment to be de-energised and the risk is controlled by a documented safe system of work.

Arc flash hazards: an arc can reach thousands of degrees; keep clear of energised equipment, use correct PPE and follow the switching program.

Tool and equipment inspection: damaged leads, cracked cases and missing earth pins must be removed from service and tagged out.

Housekeeping: keep walkways clear, store materials safely, and remove combustible waste from areas near energised equipment.

Emergency procedures: know the location of the main switch, first-aid kit, fire extinguisher and emergency contacts before starting work.

Incident investigation identifies the root cause, not just the immediate cause, so controls can prevent recurrence.

Efficiency η = output power ÷ input power × 100%; losses appear as heat in conductors, magnetic circuits and bearings.

Motor output power (mechanical) = input electrical power × efficiency; input power = √3 × VL × IL × cos φ for a three-phase motor.

Torque and speed: mechanical power P = torque (N·m) × angular velocity (rad/s); angular velocity = 2πn/60 for speed n in rpm.

Energy management: variable-speed drives reduce motor energy use by matching speed to load, since power varies approximately with the cube of speed for fans and pumps.

Power factor correction reduces line current and losses; the capacitor kVAR required = P × (tan φ1 − tan φ2).

Load profiling identifies when peak demand occurs; shifting loads off peak reduces demand charges.

Lighting efficiency is measured in lumens per watt; LED lamps typically achieve far higher efficacy than incandescent lamps.

Maintenance planning: scheduled inspection of terminations, thermal imaging of switchboards and cleaning of ventilation reduce failures and energy losses.

Employability skills for electrotechnology include communication, teamwork, problem solving, initiative, planning, self-management, learning and technology.

An apprenticeship combines paid employment with structured training; competency is assessed in the workplace and at a registered training organisation.

A training plan lists the units of competency and the workplace tasks that provide evidence for each unit.

Workplace evidence includes job records, supervisor reports, photographs of completed work and third-party reports signed by a qualified person.

Safety culture depends on reporting hazards and near misses without blame; near-miss reports are leading indicators of risk.

Ethical conduct: do not perform work outside your licence or competence, do not falsify test results, and report defects honestly.

Client communication: explain the fault, the repair options and the cost before proceeding; confirm approval for variations in writing.

Career pathways include electrical fitter, electrician, instrument technician, electronics technician and engineering associate, each with defined licensing requirements.

A switchboard distributes supply to final subcircuits; it contains the main switch, protective devices, neutral bar and earth bar.

MEN (multiple earthed neutral) system: the neutral bar is linked to the earth bar at the main switchboard only; a second link downstream creates parallel earth paths and is not permitted.

Equipotential bonding connects metallic water, gas and structural services to the main earthing conductor to limit touch voltage.

Circuit separation: safety services such as fire alarms and emergency lighting must not share a final subcircuit with general power or lighting.

Socket-outlet circuits require RCD protection; lighting circuits in domestic installations also generally require RCD protection under current wiring rules.

Cable installation: avoid sharp bends, support cable at the required intervals, and protect cable passing through metal framing with grommets or conduit.

Switchboard labelling must identify each circuit, and the main switch must be marked; a schedule of circuits is kept at or near the board.

Verification after alteration includes confirming the altered circuit is correctly identified, tested and documented in the certificate.

A variable-speed drive converts fixed-frequency supply to a variable-frequency, variable-voltage output to control motor speed.

A soft starter limits starting current by reducing voltage during start; it does not control running speed.

Sensors and transducers convert physical quantities into electrical signals: temperature (thermocouple, RTD), pressure, flow, level and position.

A 4–20 mA current loop is used for industrial signals because current is unaffected by cable resistance; 4 mA represents the zero or live zero.

A PLC digital input is typically 24 V d.c. or 240 V a.c.; analogue inputs accept 0–10 V or 4–20 mA signals.

Control circuit protection: control transformers and fuses protect the control circuit; the emergency stop must remove power from the controlled equipment.

Instrument loop testing verifies the signal from sensor to controller and the output to the final control element.

Fault finding in control systems: check the power supply, then inputs, then program logic, then outputs, using the ladder diagram as the reference.

Electrical licence requirements vary by state and territory; unlicensed electrical work is an offence and may void insurance.

Regulatory bodies administer electrical safety law: the state electrical safety regulator licenses workers and investigates incidents.

Australian Standards relevant to the trade include AS/NZS 3000 (wiring rules), AS/NZS 3008 (cable selection), AS/NZS 3760 (in-service testing) and AS/NZS 4836 (safe working on low-voltage installations).

Codes of practice give practical guidance on how to meet the duties in WHS legislation; they are admissible as evidence of compliance.

Consumer protection law prohibits misleading conduct about the work performed, the price and the qualifications of the worker.

Privacy obligations apply to client records and personal information collected during jobs.

Environmental legislation controls the handling and disposal of hazardous waste such as refrigerant, asbestos and e-waste.

Insurance and indemnity: professional indemnity and public liability cover protect the business and the client against loss from the work.

A fault-loop impedance test confirms that sufficient fault current will flow to operate the protective device within the required time.

RCD testing: press the test button and use an RCD tester to measure trip time and trip current; a 30 mA RCD should trip within the specified time at rated residual current.

Polarity testing confirms active and neutral are correctly connected at socket outlets and switches are in the active conductor.

Insulation resistance is measured between active and neutral, active and earth, and neutral and earth, with the supply isolated and sensitive equipment disconnected.

Continuity of the protective earthing conductor is measured from the main earthing terminal to each outlet earth; the result must be low and consistent.

Voltage drop verification compares measured or calculated drop against the limits in AS/NZS 3000; excessive drop causes poor equipment performance.

Test results must be recorded on the appropriate form and retained; they form part of the compliance certificate.

A residual current device with a rated residual current of 30 mA is the standard for personal protection in socket-outlet circuits in domestic installations.

A circuit breaker's breaking capacity must exceed the prospective fault current at its installation point.

Selectivity: the upstream protective device should not operate before the downstream device for a fault in the downstream circuit.

Cascading uses the current-limiting action of an upstream device to protect a downstream device with a lower breaking capacity; it must be verified by the manufacturer.

Cable insulation temperature ratings: 75 °C or 90 °C for common thermoplastic and thermosetting cables; the rating limits the current-carrying capacity.

Conductor material: copper has lower resistivity than aluminium; aluminium requires larger cross-sections and special termination techniques to avoid oxidation.

Flexible cords are rated for appliances and portable equipment; they must not be used as fixed wiring.

Enclosure IP rating: the first digit is protection against solids and the second against liquids; IP44 is splash-proof and suitable for many outdoor locations.

Hazardous areas require equipment certified for the zone and gas or dust group; ordinary equipment must not be installed in a classified area.

Energy efficiency of a building depends on lighting, HVAC, hot water and equipment loads; sub-metering identifies the major consumers.

Power quality issues include voltage sag, harmonics, transients and unbalance; each can damage equipment and increase losses.

A surge protective device diverts transient overvoltages to earth; it is installed at the main switchboard and at sensitive equipment.

Neutral sizing: in installations with high harmonic content, the neutral may need to be larger than the phase conductor.

Standby generators must be connected through a changeover device that prevents parallel connection with the supply (no backfeed).

Uninterruptible power supplies maintain supply to critical loads; an online UPS provides continuous double conversion.

Solar PV systems require a compatible inverter, correct d.c. isolators and labelling at the switchboard to warn of a second supply.

Electric vehicle charging circuits require dedicated protection, RCD type appropriate for d.c. leakage, and cable sized for continuous load.

Measurement error: accuracy is expressed as a percentage of full-scale deflection or of reading, depending on the instrument specification.

A clamp meter should be clamped around a single conductor; clamping around a cable containing active and neutral reads near zero because the currents cancel.

A multimeter's internal resistance affects the circuit: a voltmeter with low resistance loads the circuit and reads low.

An insulation tester applies a high voltage; never use it on a circuit containing electronic equipment that is not rated for the test voltage.

A phase sequence indicator confirms the order of the three supply phases before connecting a three-phase motor.

Calibration records show the instrument's traceability to a national standard; the calibration interval is set by the organisation and the manufacturer.

A proving unit verifies that a voltage tester is functioning before and after testing for dead.

Thermal imaging cameras detect hot joints and overloaded conductors by their infrared radiation; they are used for preventive maintenance.

A first-aid kit in a work vehicle should include burns dressings, sterile eyewash, gloves and a resuscitation mask.

Burns treatment: cool the burn with running water for at least 20 minutes, remove jewellery and clothing not stuck to the skin, and cover with a sterile non-stick dressing.

Cardiopulmonary resuscitation: 30 compressions to 2 breaths for adults, at a rate of 100–120 compressions per minute, with a depth of about one third of the chest.

An automated external defibrillator analyses the heart rhythm and delivers a shock if indicated; follow its voice prompts.

Electrical contact can cause entry and exit burns and internal injury; always seek medical assessment even if the casualty appears unharmed.

Falls from ladders and scaffolds are a common electrotechnology injury; secure the ladder at a 4:1 angle and maintain three points of contact.

Hazardous substances require a safety data sheet (SDS) to be available at the workplace, and appropriate ventilation and PPE for use.

Manual handling injuries are prevented by assessing the load, planning the lift, keeping the load close and avoiding twisting.

A wiring diagram shows the physical connections and terminal numbers, while a schematic shows the logical function; both are used together for fault finding.

A circuit schedule lists each circuit's number, description, protective device rating, cable size and length.

A bill of materials supports procurement and estimating; it lists quantities, descriptions and part numbers.

A test report records the instrument used, its calibration date, the test performed, the result and the acceptance criterion.

A job card records the labour hours, materials used and work performed for costing and invoicing.

A permit to work documents the isolation, the person responsible and the time limits for work on or near energised equipment.

A handover document gives the client operating instructions, test results, warranty information and maintenance requirements.

Version control of drawings and procedures ensures workers use the current revision; superseded documents must be removed from use.

A transformer's core is laminated to reduce eddy current losses; windings are insulated from each other and from the core.

An isolation transformer provides galvanic separation between primary and secondary; it does not by itself protect against contact with both secondary conductors.

Three-phase transformer connections: star-star, delta-delta, star-delta and delta-star; the connection affects the phase shift and the availability of a neutral.

An autotransformer has a single winding with a tapped connection; it does not provide isolation.

Instrument transformers: a current transformer steps current down for measurement; the secondary must never be open-circuited while the primary is energised.

A generator converts mechanical energy to electrical energy by electromagnetic induction; the output frequency depends on speed and pole pairs.

A synchronous motor runs at synchronous speed; an induction motor runs slightly below synchronous speed, with slip.

Slip s = (ns − nr)/ns, where ns is synchronous speed and nr is rotor speed; slip increases with load.

A circuit's protective device must be selected so that its rated current is not less than the design current and not more than the cable's current-carrying capacity.

Design current for a resistive load is P/V; for a motor it is the full-load current from the nameplate, adjusted for the actual supply voltage.

Diversity applies to domestic installations: not every appliance operates at once, so the maximum demand is less than the connected load.

Voltage drop limits in AS/NZS 3000 are commonly 5% of nominal voltage for the installation; check the current edition for the applicable value.

Earth fault-loop impedance must satisfy the formula Zs ≤ U0/Ia, where Ia is the current that operates the protective device within the required time.

A final subcircuit supplying a single socket outlet may be protected at a lower rating than a circuit supplying multiple outlets.

Cable grouping derating applies when cables are bunched or enclosed; the factor is read from AS/NZS 3008 tables.

Ambient temperature derating uses the correction factor for the expected maximum ambient temperature at the installation location.

A digital multimeter measures voltage, current, resistance, continuity and sometimes capacitance and frequency; select the correct function and range before use.

A megger (insulation resistance tester) applies 250 V, 500 V or 1000 V d.c. depending on the circuit voltage rating.

An earth tester measures earth electrode resistance using a fall-of-potential or clamp method.

A loop impedance tester measures the earth fault-loop impedance while the circuit is energised; it must be used with the correct leads and settings.

An RCD tester measures trip time and trip current at half, full and five times rated residual current.

A phase rotation meter indicates the sequence of the three phases; a positive sequence is required for correct motor direction.

A cable fault locator uses time-domain reflectometry or a bridge method to locate open or short circuits in buried or long cable runs.

A power quality analyser records voltage, current, harmonics and transients over time to diagnose intermittent problems.

A safe isolation procedure: identify the circuit, notify affected persons, isolate, lock and tag, prove the tester, test for dead, and prove the tester again.

A lock-out device must be personal to the worker; group lock-out uses a hasp so each worker applies their own lock.

A tag alone is not a lock; tags communicate information but do not prevent operation.

Isolation must be at a point that cannot be inadvertently re-energised, and the isolation point must be under the worker's control.

Testing for dead must be done at the point of work, on all conductors, and with a tester rated for the voltage present.

If the isolation point cannot be locked, an alternative control such as removing fuses and keeping them in the worker's possession is used.

Before restoring supply, confirm all workers are clear, tools are removed, and the equipment is reassembled and guarded.

The person who isolated the circuit is responsible for removing the lock and tag after confirming it is safe to re-energise.

A short circuit has very low resistance and causes a high current; the protective device must operate quickly to limit damage.

An open circuit has infinite resistance; the symptom is no current flow and no voltage across the load in a series circuit.

A high-resistance joint causes a voltage drop and heating; it is found by measuring voltage across the joint under load.

Fault finding sequence: verify the fault, gather information from the user and drawings, isolate, test in sections, repair, then retest and document.

Half-split fault finding tests the middle of a circuit to determine which half contains the fault, reducing the number of tests.

Substitution replaces a suspected component with a known good one to confirm the fault; it is used only when safe and appropriate.

Intermittent faults are often caused by loose connections, damaged cable or thermal effects; they may require monitoring over time.

After repair, the circuit must be retested to confirm the fault is cleared and no new fault has been introduced.

A star-delta starter reduces starting current by connecting the motor in star during start and delta during run; the changeover must be interlocked.

A reversing starter uses two contactors with electrical and mechanical interlocking and swaps two supply phases.

A contactor's coil voltage is selected to match the control circuit; the contact rating must exceed the load current.

An overload relay's setting is the motor full-load current; a Class 10 relay trips within 10 seconds at six times the set current.

A thermal overload relay does not protect against short circuit; a short-circuit protective device must be installed upstream.

A no-volt release prevents automatic restart after a supply failure; the operator must deliberately restart the motor.

A soft starter or variable-speed drive reduces mechanical stress on the driven equipment during start.

Motor control circuit diagrams show the control devices in their de-energised state; the ladder is read left to right and top to bottom.

A d.c. motor's speed is approximately proportional to armature voltage and inversely proportional to field flux; a d.c. drive controls both.

Back EMF opposes the applied voltage and limits armature current; it is proportional to speed and field flux.

A shunt motor has field and armature in parallel; a series motor has high starting torque and must never be run unloaded.

A universal motor runs on a.c. or d.c. and is used in portable power tools.

A stepper motor moves in discrete steps; the step angle is 360° divided by the number of steps per revolution.

A servo motor uses feedback to control position, velocity or torque; a closed-loop controller compares the command with the feedback signal.

A variable-frequency drive controls induction motor speed by varying the supply frequency; the voltage is varied with frequency to maintain flux.

Braking methods include regenerative, dynamic and mechanical braking; regenerative braking returns energy to the supply.

A soldered joint must be mechanically secure before soldering; a dry joint has poor wetting and high resistance.

Crimp terminations require the correct die and tool for the terminal type; the crimp is inspected for wire strands outside the barrel.

Cable glands provide mechanical support, strain relief and environmental sealing; the correct gland size matches the cable diameter.

Conduit installation: bends must not be too tight, conduit must be supported at intervals, and cable fill must not exceed the permitted percentage.

Cable tray and ladder installations require earthing of metallic tray and bonding across joints.

Underground cable must be buried at the required depth, protected by a marker tape or conduit, and recorded on the as-built drawing.

Fire-rated cable and sealing are used where a circuit must maintain integrity during a fire, such as emergency lighting and fire pumps.

Labelling of cables and cores at both ends aids fault finding and future maintenance.

A circuit's design current must be calculated before selecting cable and protection; the design current is the expected maximum current in normal use.

Protective device types: a Type B MCB trips magnetically at 3–5 times rated current, Type C at 5–10 times and Type D at 10–20 times.

Type B devices suit resistive loads; Type C suits inductive loads such as motors; Type D suits high-inrush loads such as transformers.

A fuse's time-current characteristic shows that it operates faster at higher currents; the let-through energy must be less than the cable's withstand.

An RCD does not protect against overload or short circuit; it must be used with overcurrent protection.

An RCBO combines overcurrent and residual current protection in one device.

A main switch isolates the whole installation; it must be capable of being locked in the off position.

A surge protective device must be coordinated with the protective devices downstream so that it does not cause nuisance tripping.