EWRB Electrical common mistakes
EWRB Electrical · Understand the traps and how to avoid them.
Calculating load current as I = P ÷ V for every load, with no power-factor or efficiency term, then carrying that number into cable-size and protection selections.
The candidate has memorised the DC/unity-power-factor form of the power equation and treats motor, discharge-lighting and welder loads as if they were resistive. It feels like a shortcut but changes the current by 20–60%.
What to do instead
Before any cable or protection calculation, build a small load schedule: list each load, its VA or kW, its power factor and, for motors, its efficiency. Convert to current with I = P ÷ (V × pf × efficiency) for single phase and the line-current equivalent for three phase, and state the assumed pf in the answer.
Mixing line and phase quantities in three-phase star/delta questions, e.g. using 400 V where the phase voltage of 230 V belongs, or forgetting the √3 in line current for a delta load.
The candidate learns '400 V three phase' as a single number and never sketches the star/delta relationship. Without a diagram the √3 factor is applied by guesswork.
What to do instead
Draw the star or delta connection at the top of every three-phase answer and label V_L, V_Ph, I_L, I_Ph before touching the calculator. Apply V_L = √3·V_Ph (star) and I_L = √3·I_Ph (delta) from the diagram, then check the answer against a sanity figure such as a 400 V, 10 kW unity-pf load drawing about 14.4 A.
Using the published mV/A/m voltage-drop figure without checking whether it is for three-phase or single-phase, or omitting the neutral/active return path length, giving a volt drop roughly half the true value.
Tables quote different factors for different circuit arrangements and the candidate grabs the first number on the row. In single-phase circuits the current flows out and back, so the run length doubles.
What to do instead
Write the formula first (Vd = mV/A/m × I × L ÷ 1000, with L the route length for three-phase and twice the route length for single-phase), state which arrangement the table figure belongs to, and finish by expressing the result as a percentage of 230 V or 400 V and comparing it with the AS/NZS 3000 limit.
Not distinguishing between prescribed electrical work that must be inspected and certified, work that may be self-certified, and maintenance work that needs no certificate - and writing answers as if every job needs the same paperwork.
Candidates study the Wiring Rules in detail but skim the Electricity (Safety) Regulations, so the regulatory layer that decides who may do what, and who must inspect it, is learned as isolated facts rather than a decision path.
What to do instead
Build a one-page decision flowchart from memory: what is the work, is it prescribed, is it high-risk, who is licensed to do it, does it need inspection by an independent licensed inspector, and what certificate(s) must be issued to the owner. Practise classifying a dozen real jobs (new socket-outlet in a kitchen, replacement of a light switch, new submains, appliance repair) through that flowchart.
Citing AS/NZS 3000 as if it were legislation ('the Wiring Rules require...') or quoting a clause number from memory that does not match the current edition.
The Wiring Rules are the document most often read, so they become the mental default. Clause numbering also differs between editions, and candidates revise from older notes.
What to do instead
In every written answer, separate the two layers explicitly: 'the Regulations require X; AS/NZS 3000, as cited, provides the means of compliance Y'. When you cannot recall a clause number with certainty, cite the section topic instead of inventing a number - a correct principle with a vague reference scores better than a precise-sounding wrong reference.
Leaving the certification form incomplete: test results written as 'OK' or 'satisfactory' rather than numbers, max demand not stated, the extent of work described only vaguely, and no record of the tests actually performed.
Candidates treat the certificate as an administrative signature rather than a test record, and in practice they have often seen completed forms that were filled in perfunctorily.
What to do instead
Practise completing a blank certificate for a described job, field by field, with a checklist beside it: description and extent of work, supply characteristics, max demand, each test with instrument, value and pass/fail, and the declaration and signature. Every test entry must be a number and a unit; if a value is absent, the job is not finished.
Reaching for the wrong standard: using AS/NZS 3760 in-service testing logic for a new installation, quoting AS/NZS 3017 as a design standard, or answering safe-working questions from the Wiring Rules instead of AS/NZS 4836.
Several standards contain overlapping test methods, so the candidate recalls the test but not which document governs the situation, and answers a verification question with an in-service-testing procedure.
What to do instead
Keep a short mapping table in your revision notes: AS/NZS 3000 for design and verification of installations; AS/NZS 3017 for verification test methods; AS/NZS 3760 for in-service testing and tagging of equipment; AS/NZS 4836 for safe working on low-voltage installations; product standards for equipment. Before answering, name the situation in one phrase and select the document from the table.
Isolating one supply, then treating the circuit as dead without proving it at the point of work - or proving with a tester that was not proved before and after the test.
The candidate's mental model is 'I turned it off at the board', which ignores multiple supplies, UPS, embedded generation, borrowed neutrals and control circuits. The tester itself is assumed to work.
What to do instead
Use a fixed prove–test–prove routine every time: prove the tester on a known live source or proving unit, test every conductor at the point of work including neutral and earth, then re-prove the tester. Before isolation, trace and identify every source feeding the enclosure and record it; treat any conductor you have not personally proved as live.
Running verification tests in the wrong order or with the wrong instrument settings - insulation resistance before the visual inspection and before disconnecting electronics, or using the wrong test voltage and then recording a fail.
Candidates memorise the list of tests but not the sequence logic, so they perform insulation resistance on a board still carrying surge protection and get a low reading, then either pass it or waste time.
What to do instead
Learn and rehearse one fixed sequence: visual inspection, then continuity of protective earthing and bonding, then polarity, then insulation resistance with sensitive equipment isolated and the correct DC test voltage for the circuit voltage, then earth fault loop impedance, then RCD operation (with trip time), then function. State the sequence, the instrument and the acceptance limit in the answer, not just the test name.
Signing off or supervising work without being able to describe the supervision actually given - no record of who did which part, no check of the trainee's work before certification, and no evidence of testing after the trainee finished.
Supervision obligations are treated as a status ('I'm the licensed person') rather than as a set of actions, and in a busy job the paperwork is completed at the end from memory.
What to do instead
For any scenario question, describe supervision as observable actions: what was checked, when, by whom, what test results were reviewed and what was corrected. Keep a supervision record on the job as work proceeds, and only certify work you have personally inspected and tested or had inspected and tested under your direction.