NSW Electrical Licence common mistakes
NSW Electrical Licence · Understand the traps and how to avoid them.
Calculating voltage drop using the total load current and the one-way circuit length instead of the load current at the far end and the full route length (out and back), then declaring the cable compliant.
Candidates learn Vd = I × R by rote and treat the length as a single span, forgetting that the loop resistance includes the neutral/return conductor; they also plug in the protective device rating rather than the actual design current, which overstates or understates the result.
What to do instead
Always write the formula out with units before substituting: Vd = (mV/A/m × I_b × L) / 1000, where L is the one-way route length in metres and the mV/A/m value already accounts for the loop. Check the result as a percentage of nominal voltage against the limits in AS/NZS 3008.1.1 (typically 5% for power, 3% for lighting from the point of supply) and state the limit explicitly in your working.
Selecting a cable from the current-carrying capacity table without applying the derating factors for grouping, ambient temperature, and thermal insulation, or applying them in the wrong order.
The tabulated current-carrying capacity is a reference figure under standard conditions; candidates see a number above the design current and stop, missing that the installation conditions change the effective rating.
What to do instead
Work the calculation as I_t ≥ I_b / (k_1 × k_2 × k_3 ...), where each k is a derating factor from AS/NZS 3008.1.1. Identify each applicable factor from the installation method, then divide before comparing to the table. If any factor is unfamiliar, state the assumption and flag it rather than omitting it.
Confusing the roles of the main earthing terminal, the protective earth conductor, and the neutral link, and describing MEN as though the neutral is earthed at every outlet.
The multiple earthed neutral system is taught with a single diagram, and candidates memorise the picture without understanding that the neutral is connected to earth at the supply point and at the main switchboard, and that the protective earth and neutral are separated at all final subcircuits.
What to do instead
Draw the system from the transformer to the load and label each bond. State the three facts in every answer: the neutral is earthed at the star point of the supply transformer, at the main switchboard via the MEN link, and nowhere downstream. Then explain that the protective earth conductor carries fault current only, and verify separation at the first outlet with an insulation resistance test between active/neutral and earth.
Choosing a residual current device rating by matching the number on the device to the circuit breaker rating rather than to the required sensitivity and the purpose of the protection.
Candidates assume RCDs are selected like circuit breakers, by current rating, and overlook that the trip sensitivity (30 mA for personal protection, higher for fire or equipment protection) and the type (AC, A, B) are the selection criteria.
What to do instead
For each RCD question, state the purpose first (personal protection, additional protection, or equipment), then the required sensitivity, then the type based on the waveform of the load. For socket outlets and lighting circuits requiring additional protection, specify 30 mA. Confirm the device rating is at least the circuit design current and that the type suits any DC or pulsating load present.
Describing the test sequence for a new installation without first confirming isolation and proving the tester, or performing insulation resistance before continuity of the protective earthing conductor.
Candidates memorise a list of tests but not the logical order, and they treat the safe isolation procedure as a preamble rather than a step that must be evidenced at each stage.
What to do instead
Use the fixed order: visual inspection, then safe isolation and prove the tester on a known source (prove–test–prove), then continuity of protective earthing conductors and bonding, then insulation resistance with sensitive equipment disconnected, then polarity, then circuit protection verification, then RCD trip times, then functional testing. Write the order out in full in any procedure question and include the prove-test-prove step explicitly.
Reporting an insulation resistance result as a single pass/fail figure without recording the test voltage, the duration, and the items disconnected during the test.
Candidates read the minimum value from a table and stop, not realising that the recorded result is only valid if the test conditions match the standard, and that disconnection of electronics and surge protection is part of the test method.
What to do instead
Record four things for every insulation resistance test: the test voltage (500 V DC for 250/440 V circuits), the minimum acceptable value (1 MΩ for a new installation), the duration until the reading stabilises, and a list of equipment isolated or disconnected. If a low reading occurs, describe the systematic sectionalisation to locate the fault rather than declaring the circuit failed.
Treating the switchboard schedule and the circuit identification as paperwork to be completed after commissioning rather than as part of the verification process.
Candidates separate the physical work from the documentation and do not connect the requirement for accurate circuit identification to the safety of anyone working on the installation later.
What to do instead
In any question about verification or handover, list the documentation as deliverables: switchboard schedule, circuit charts, test results, and the compliance certificate. Explain that each circuit must be identifiable at the switchboard and that the schedule must match the as-installed arrangement, then describe how a mismatch would be detected during the visual inspection.
Answering a fault-finding scenario by replacing components in sequence rather than by forming a hypothesis and testing it with measurements.
Candidates have seen real faults resolved by swapping a part and reproduce that behaviour in written answers, which reads as guesswork and does not demonstrate the reasoning the question is testing.
What to do instead
Structure every fault-finding answer as: gather the symptom, form a hypothesis from the circuit topology, select the measurement that distinguishes between hypotheses, predict the expected reading, then compare. For example, for a circuit that trips on a residual current device, state that a low insulation resistance to earth on one subcircuit is the likely cause, then describe the sectionalised test that would confirm it.
Describing risk controls for a task in general terms such as 'be careful' or 'wear PPE' without identifying the hazard, the hierarchy of control, and the specific control for that task.
Candidates confuse the presence of PPE with the management of risk and have not practised applying the hierarchy of control to a concrete electrical task.
What to do instead
For each task, name the hazard (for example, arc flash from an energised panel), apply the hierarchy in order (eliminate by de-energising, substitute, isolate, engineer, administrate, then PPE as the last line), and state the specific control at each level. Include the isolation and lock-out/tag-out procedure and the test-before-touch step as the primary controls, with PPE described as the residual protection.
Confusing the scope of work that may be performed under supervision with the work that requires a licensed electrician, and misstating when a compliance certificate or notification to the network operator is required.
Candidates learn the licensing categories as a list of titles and do not map them onto the actual boundary between supervised work, licensed work, and work that must be certified or notified.
What to do instead
Build a table with three columns: work type, who may perform it, and what documentation is required. Populate it for consumer mains, subcircuits, alterations to existing installations, and work on the supply side of the point of supply. For each entry state whether a certificate of compliance is required and whether the network operator must be notified before energisation.