NASCLA Journeyman Electrician common mistakes
NASCLA Journeyman Electrician · Understand the traps and how to avoid them.
Uses single-phase formulas on three-phase loads (e.g., computes current as I = P ÷ E instead of I = P ÷ (1.732 × E × PF)), and reports power in the wrong units when a problem mixes watts, VA, and vars.
Most practice problems early in study are single-phase, so the 1.732 factor and the power-factor term get dropped under time pressure; candidates also read 'kW' and 'kVA' as interchangeable.
What to do instead
Before calculating, write down the system type (1-phase or 3-phase) and the quantity asked for (W, VA, var, or amps). Drill a mixed set of 20 problems where each solution starts with the formula written out, and always carry units through the arithmetic so a wrong unit is visible.
Sizes a dwelling service by summing every connected load at 100% - general lighting, small-appliance circuits, range, dryer, water heater - without applying demand factors or the 25% largest-motor adder.
The load list on the plans looks like an addition problem, and candidates do not realize the standard calculation requires Table 220.42 lighting demand factors, Table 220.55 range demand, and the 25% largest-motor adder in 220.50/430.24.
What to do instead
Work the standard method in a fixed order every time: general lighting + small appliance + laundry at Table 220.42 demand, then appliance loads per 220.53, then the largest motor at 125%, then compare against the optional method in 220.82 if asked. Build a one-page checklist and use it on ten practice services before the exam.
Reads ampacity straight off Table 310.16 using the 90°C column for THHN and stops there, ignoring termination temperature limits and skipping any adjustment or correction.
The 90°C column gives the biggest, most satisfying number, and 110.14(C) is buried in a section candidates skim; conduit fill and ambient conditions are treated as separate topics rather than part of one calculation.
What to do instead
Use a fixed four-step sequence: ampacity from Table 310.16 limited by the termination rating (60°C for ≤100 A unless equipment is listed otherwise, per 110.14(C)), then ambient correction from 310.15, then Table 310.15(C)(1) adjustment for current-carrying conductors, then compare to the OCPD. Practice until the sequence is automatic.
Calculates box fill by counting only the current-carrying conductors, forgetting that each yoke counts as two conductors of the largest size, each cable clamp counts as one, and all equipment grounding conductors together count as one.
Physically, a box with two cables and a receptacle 'feels' like four conductors, so candidates count what they can see rather than applying the itemized list in 314.16(B).
What to do instead
Do a written tally in 314.16(B) order - conductors, EGCs (as one), clamps, yokes (2 each), then multiply by the volume per conductor from Table 314.16(B) and compare to the box volume from Table 314.16(A). Do six practice boxes, including a mixed-size box where the largest conductor governs.
Selects the equipment grounding conductor from Table 250.66 or the grounding electrode conductor from Table 250.122 - effectively swapping the two tables - and sizes a GEC from the breaker rating instead of the service conductor.
Both tables look alike and are studied in the same week; the mental link 'bigger breaker, bigger ground' is intuitive and produces a plausible-looking wrong answer.
What to do instead
Anchor each table to its trigger: 250.66 is keyed to the largest service-entrance or feeder conductor and applies to the grounding electrode conductor; 250.122 is keyed to the rating or setting of the overcurrent device and applies to equipment grounding conductors. Rewrite both rules from memory twice a week and check each practice answer against the trigger, not the table number.
Uses the nameplate current for the motor branch-circuit conductor and short-circuit protection sizing, and uses the Table 430.250 value for overload sizing - the rules reversed.
Nameplate amps are the only number actually visible, so they get used everywhere; candidates do not internalize that 430.6(A)(1) sends you to the tables for conductors and branch-circuit protection but back to the nameplate for overloads.
What to do instead
Memorize the split as a phrase: 'Tables for wire and breaker, nameplate for overloads.' Then work a motor problem end to end - Table 430.250 FLC × 125% for conductors per 430.22, Table 430.52 percentage for the short-circuit device, nameplate FLA × the 430.32 percentage for overloads - and repeat for a NEMA Design B and a Design E motor.
Applies a single percentage to the transformer primary and assumes the secondary is covered, instead of determining whether the installation is primary-only protection or primary-and-secondary protection under Table 450.3(B).
Table 450.3(B) is a matrix with two distinct columns, and the exam question usually hides which condition applies in the wording about the secondary device; candidates read the first number they see and move on.
What to do instead
Before answering, decide explicitly: is there a secondary OCPD within the required distance? If yes, use the primary-and-secondary column and check both percentages; if no, use the primary-only column and recall the 125%/250% values for the relevant range. Also check 240.21(C) whenever the secondary conductors are more than a short distance from the transformer.
Treats a dwelling-unit bathroom receptacle as an ordinary general-purpose outlet - fed from the lighting circuit and placed wherever there is wall space - and applies 210.52 spacing rules inside the bathroom.
Bathrooms are studied under 'special locations' but the receptacle rules candidates memorize are the 6 ft/12 ft wall-spacing rules; nobody notices that 210.52 does not govern bathroom receptacles and 210.11(C)(3) does.
What to do instead
Build a short table of special-location receptacle requirements - bathroom (20 A circuit supplying only bathroom receptacles, GFCI per 210.8), kitchen counter (two or more 20 A small-appliance circuits, no more than 600 mm below the countertop), laundry, garage, outdoors - and recite it before each practice set. Add a note that tamper-resistant requirements apply to dwelling units.
Chooses shock and arc-flash PPE from memory by recalling 'category 2' or 'category 3' rather than looking up the incident-energy or arc-flash-hazard-risk tables, and mixes up the limited, restricted, and prohibited approach boundaries.
PPE categories are the most familiar numbers in NFPA 70E, so they feel safe to recall; boundary distances feel interchangeable because they are all measured in feet from energized equipment.
What to do instead
Learn the order of the boundaries (limited, then restricted, then prohibited, getting closer) and always jump to the arc flash PPE tables now used in 70E instead of recalling a category. Practice ten lookups where you find the table by equipment type and task, since the exam tests navigation speed as much as memory.
Reads only the floor plan and ignores the panel schedule, one-line diagram, and drawing scale when answering feeder or raceway questions - guessing conduit and conductor sizes from the branch circuit rather than the feeder shown on the schedule.
The floor plan is the biggest, clearest drawing; schedules are small print in a corner, and candidates do not convert scaled dimensions, so a scaled 40 ft run gets answered as 'about 30 ft'.
What to do instead
Adopt a fixed scan order for every drawing question: title block and notes, one-line diagram, panel schedule, then the plan view, and only then compute. Practice three or four plan-reading problems where you must state the feeder size from the schedule before you answer anything about the circuit.