ID Electrician common mistakes
ID Electrician · Understand the traps and how to avoid them.
Answering code questions from field habit or 'what we always do' instead of from the actual Code text, and treating Informational Notes and Fine Print Notes as enforceable requirements.
Years of jobsite practice create strong default answers; candidates skim the question, recognize a familiar installation, and pick the answer that matches their own work rather than the wording in the NEC.
What to do instead
Before answering any code question, locate the governing article and read the exact sentence. Drill the distinction between 'shall,' 'shall be permitted,' and Informational Notes (Article 90.5). For every practice question, write the article/section number next to your answer; if you cannot cite it, mark the question as a guess and review it.
Searching the Code by paging sequentially from Article 100 forward, or answering from a remembered article number, instead of using the index and the Table of Contents hierarchy.
The exam is time-limited and candidates have not built fluency with the NEC's structure (Chapters 1-4 general, 5-7 special, 8 communications, 9 tables), so they hunt page by page and burn minutes.
What to do instead
Practice timed index drills: take 25 random topics (e.g., 'trade size of rigid PVC in corrosive area,' 'ampacity of fixture wire') and find the article in under 30 seconds each using the index, then confirm with the TOC. Memorize the chapter map and Article 100 definitions, since definitional questions are answered there, not in the wiring-method articles.
Selecting a wiring method based only on ampacity and cost, without checking the restrictions the specific article places on that method for the occupancy or location (for example, using a nonmetallic-sheathed cable where the applicable article prohibits it, or a raceway type not permitted in the environment).
Candidates study ampacity tables heavily but skim the 'Uses Permitted' and 'Uses Not Permitted' sections at the start of each wiring-method article, and they forget that Chapter 5 occupancy articles and 300.22 can further restrict a method.
What to do instead
For every wiring-method question, run a fixed checklist: (1) open the wiring-method article and read Uses Permitted / Uses Not Permitted, (2) check Article 300 for the general location rule, (3) check the Chapter 5 article for the occupancy, (4) then size the conductor. Build a one-page comparison grid of the methods you use most so the restrictions are memorized.
Miscalculating box fill, typically by counting each device or each cable clamp as one conductor, forgetting the equipment grounding conductors, or forgetting that the largest conductor's volume allowance applies to the EGC count.
Candidates memorize 'one count per conductor' but not the Table volume allowances and the specific counting rules, and they count from the picture rather than from a written list, so items get double-counted or dropped.
What to do instead
Write out the count as a list every time: current-carrying conductors, then EGCs (counted using the largest conductor's allowance), then devices (two conductors per yoke for a single device on a 14/12 AWG circuit), then clamps, then support fittings, then one allowance for one or more grounds. Multiply by the Table 314.16(B) volume per conductor size and compare to the box volume from Table 314.16(A) or the marked volume.
Applying the 'next higher standard overcurrent device' allowance to situations where it is prohibited, such as branch circuits supplying two or more receptacles (multioutlet) or where the conductor ampacity exceeds 800 A.
The rule is memorable and easy to apply, so candidates apply it as a default whenever the device rating does not match the conductor ampacity, missing the explicit exceptions in the section.
What to do instead
Before applying the next-size-up allowance, state aloud the two prohibitions and check the circuit type: if it is a multioutlet receptacle branch circuit or the ampacity is over 800 A, round down instead. Practice with 10 mixed scenarios and label each 'round up permitted' or 'round down required.'
Forgetting the continuous-load 125% factor when sizing branch-circuit or feeder overcurrent protection, or applying it to the conductor but not the device (or vice versa).
Candidates size the conductor from the load and then pick a breaker from the same number, treating conductor sizing and overcurrent device sizing as one calculation when they are two, each with its own adjustment rules.
What to do instead
Use a two-column worksheet on scratch paper for every branch-circuit and feeder question: left column for conductor ampacity (including any adjustment or correction factors), right column for the overcurrent device (continuous load x 125% plus noncontinuous load). Size each independently, then check the small-conductor limits and the device must protect the conductor.
Using the grounding electrode conductor table when the equipment grounding conductor table is called for, or vice versa, because both are 'the green wire' sizing tables.
The two tables serve different purposes (system grounding versus fault-current return path) and candidates conflate them under the single mental label 'grounding,' often because they memorize one table and reuse it.
What to do instead
Before sizing any grounding or bonding conductor, answer two questions in writing: 'Is this the electrode conductor from the service to earth, or the equipment conductor providing the fault path?' and 'Is it sized from the service conductor or from the overcurrent device rating?' Electrode conductors size from the service conductors; equipment grounding conductors size from the rating of the overcurrent device ahead of the circuit.
Treating a ground-fault circuit interrupter as a substitute for an equipment grounding conductor or for bonding, and choosing a GFCI answer whenever shock protection is the topic.
GFCI and grounding both get filed mentally under 'safety,' so candidates pick the protective device even when the question is about the fault-current path, metal raceway bonding, or continuity of the equipment grounding conductor.
What to do instead
For every safety question, first classify it as one of three: (1) intentional earth connection of the system, (2) bonding of metal parts to provide the low-impedance fault path, or (3) supplemental person protection by sensing imbalance. Only category 3 is a GFCI. Write the classification next to the question before looking at the answers.
Sizing motor branch-circuit conductors directly from the conductor ampacity table using the nameplate current, instead of using the motor full-load current tables and applying the required percentage increase.
The motor articles route you to separate tables that do not exist for other loads, and candidates carry over the general branch-circuit method from lighting and receptacle practice, or they read nameplate current that is used for a different purpose.
What to do instead
For motor questions, follow a fixed order: find the motor full-load current from the motor tables; multiply by the required percentage to size branch-circuit conductors; separately size the short-circuit and ground-fault protective device from its own table and rules; separately size the overload device from the nameplate current. Never use the nameplate current for conductor ampacity.
Answering the licensing portion from general trade knowledge or from another state's rules, without having studied Idaho's electrical statute and the board's administrative rules.
Candidates spend almost all preparation time in the NEC and assume the administrative portion is common sense, but licensure scope, contractor and qualifier responsibilities, and enforcement procedures are set by state law and board rule, not by the Code.
What to do instead
Build a separate one-page summary of the Idaho electrical licensing statute and the board's rules covering license classes, scope of work each class may perform, contractor and qualifier obligations, permitting and inspection authority, and disciplinary grounds. Review that page weekly and answer at least a few administrative questions in every practice session. Verify current text on the state licensing board's official site, since rules are amended.