CIC Grade A Electrical Trade Test common mistakes
CIC Grade A Electrical Trade Test · Understand the traps and how to avoid them.
When calculating conduit fill, the candidate adds up the cross-sectional areas of the conductors and compares the total directly against the internal area of the conduit, ignoring the 40% maximum-fill limit for three or more conductors.
Many candidates memorise the conduit internal areas and the conductor areas but never internalise the fill-percentage rule, so they treat the conduit as a simple container rather than applying the code-mandated percentage caps (often 40% for over two conductors). They also confuse the different limits that apply to one, two, and three-or-more conductors.
What to do instead
Before any fill calculation, write down the three percentage limits (for example 53% for one conductor, 31% for two, 40% for three or more, per the applicable wiring regulation) and state which one applies to the conductor count in the question. Then compute total conductor area, divide by conduit internal area, and compare against the correct percentage. Practise with a table of common conduit sizes and conductor areas until the percentage check becomes automatic.
The candidate sizes the protective device from the connected load or the design current alone, without checking that the tabulated current-carrying capacity of the chosen cable, after applying every correction factor, is at least equal to the device rating.
Candidates often work forward from the load and stop once they have a device rating, forgetting the verification step that the cable must be able to carry that current under the actual installation conditions. Correction factors for ambient temperature, grouping, thermal insulation, and protective-device type are frequently skipped or applied to the wrong base value.
What to do instead
Adopt a fixed sequence: design current, then nominal device rating, then apply all correction factors to the tabulated cable capacity, then confirm the corrected capacity is not less than the device rating. Show each correction factor as a separate line with its source value. Do timed drills where the answer is only marked correct if every factor is listed.
When asked to determine earth-fault loop impedance or disconnection time, the candidate uses the nominal supply voltage and the measured or calculated loop impedance but never checks the result against the maximum permitted disconnection time for that circuit type.
The calculation feels complete once a current value is produced, so candidates stop before the compliance comparison. They also mix up the disconnection times that apply to final circuits versus distribution circuits, and to TN versus TT systems, so they compare against the wrong limit.
What to do instead
Treat every loop-impedance question as a two-part answer: first compute the fault current, then state the required disconnection time for that circuit and system type and confirm the device will operate within it. Keep a one-page summary of disconnection times by circuit and system type and recite it before attempting these questions.
The candidate reads a wiring diagram or schedule and answers from the first plausible interpretation without tracing the circuit end to end, missing series elements, normally-closed contacts, or parallel paths that change the expected behaviour.
Under time pressure, candidates pattern-match on familiar symbols and assume standard arrangements. Control circuits with latching contacts, emergency-stop chains, or interlocking are especially prone to being misread because the logic is not linear.
What to do instead
Physically trace each circuit from supply to load, naming every component in order and stating whether each contact is normally open or normally closed in the de-energised state. For control circuits, write the logic in words (for example 'the contactor holds itself in through the auxiliary contact') before selecting an answer.
When selecting or installing a residual current device, the candidate treats all RCDs as interchangeable and does not distinguish between the types by waveform sensitivity or between the rated residual operating current and the rated current.
Candidates learn the 30 mA figure for additional protection and then apply it to every RCD question, overlooking that some equipment produces pulsating or smooth direct residual currents that require a specific RCD type. They also confuse the device's current rating with its residual operating current.
What to do instead
Build a short reference card listing RCD types, the residual current waveforms each detects, and typical applications. For every RCD question, explicitly state the required residual operating current, the required type, and the reason. Check that the device's rated current is not less than the circuit's design current.
The candidate calculates voltage drop using the full circuit current and the one-way cable length, then compares the result against the permissible percentage without doubling the length for the return path.
Textbook examples often present voltage drop formulas in a form where the length factor is already embedded, and candidates lose track of whether the length used is one-way or the total conductor length. The mistake is silent because the resulting figure looks plausible.
What to do instead
Always write the formula with the length term labelled explicitly as total conductor length (two-way for single-phase). Sanity-check by estimating: a long run with a small conductor should show a noticeably larger drop. Practise a handful of examples where you compute both the one-way and two-way versions and compare.
In questions about protective earthing and bonding, the candidate treats circuit protective conductors and main protective bonding conductors as the same thing and applies the circuit-conductor sizing rule to the main bonding conductor.
Both are green-and-yellow conductors, so candidates conflate them. The sizing rules differ: circuit protective conductors are related to the line conductor size, while main protective bonding conductors are related to the size of the supply neutral or the earthing conductor, and there are minimum sizes.
What to do instead
Draw a simple diagram showing the earthing conductor, main protective bonding conductors, and circuit protective conductors as separate items, and write the sizing rule beside each. When answering, first identify which conductor the question is about, then apply only that rule.
The candidate answers a testing question by naming the instrument but omits the verification steps that must precede the test, such as proving the tester on a known source before and after the measurement.
Candidates focus on the measurement itself and treat instrument checks as administrative detail. They also forget that some tests require the supply isolated and others require it energised, so the sequence is muddled.
What to do instead
For every test question, give a three-part answer: safe isolation and preparation, the measurement with instrument and expected range, and the proving/confirmation step afterwards. Memorise the correct energised or isolated state for each test and rehearse the full sequence aloud.
When interpreting a protective device's time-current characteristic, the candidate reads the curve at the wrong axis scale or uses the nominal current instead of the actual prospective fault current to find the operating time.
Logarithmic axes and multiple-current multiples on the horizontal axis are easy to misread, and candidates often forget that the vertical axis gives time while the horizontal gives current as a multiple of the rating. Mixing up the two produces an answer that is off by an order of magnitude.
What to do instead
Practise reading several characteristic curves, each time stating aloud which axis you are on and what units apply. Convert the prospective fault current into a multiple of the device rating before locating it on the curve, and write that multiple down. Check the resulting time against the required disconnection time.
The candidate answers special-location or installation-condition questions from general wiring rules, ignoring the additional requirements for locations such as bathrooms, swimming pools, construction sites, or agricultural buildings.
General rules are learned first and reinforced by repetition, while special-location requirements are learned later and less often, so under pressure the candidate defaults to the general rule. The zones and their boundaries in wet locations are particularly easy to misremember.
What to do instead
Create a location-by-location summary listing the zones, the permitted equipment, the IP ratings, and the additional protection required. For any question mentioning a wet, outdoor, or temporary location, pause and ask which special requirements override the general rule before answering.