MI Journeyman Electrician common mistakes
MI Journeyman Electrician · Understand the traps and how to avoid them.
Sizing a device or junction box by counting conductors and multiplying by a single volume number, ignoring equipment grounding conductors, cable clamps, support fittings, and the volume allowance taken per device yoke.
Candidates memorize the conductor volume table but skip the extra allowance items in the box-fill rules, and they treat box fill the same way they treat conduit fill.
What to do instead
Work the box-fill problem in a fixed sequence: total the volume allowance for each conductor by size, add one allowance for all equipment grounding conductors based on the largest one, add one allowance for clamps and one for support fittings, and add one allowance for each yoke or device based on the largest conductor landing on it; then compare to the marked box volume.
Sizing the overcurrent device for a branch circuit or feeder at 100 percent of a continuous load, or applying the 125 percent continuous-load multiplier to the conductor ampacity but not the overcurrent device (or the reverse).
The continuous-load multiplier is learned as a single rule and then applied to only one side of the calculation, and receptacle/lighting loads are assumed to be noncontinuous by habit.
What to do instead
Separate the two calculations on scratch paper. Conductors: 125 percent of continuous load plus 100 percent of noncontinuous load. Overcurrent device: same 125/100 split unless the assembly is listed for 100 percent. Label each line so the multiplier is never dropped or double-applied.
Sizing an equipment grounding conductor from the grounding electrode conductor table, or sizing a grounding electrode conductor from the equipment grounding conductor table, so a 400 A service gets an undersized or oversized conductor.
Both tables use conductor-size lookups and are studied back-to-back, so the trigger for each one gets blurred.
What to do instead
Tie each table to its question: if the question asks about the conductor that runs with the circuit conductors and carries fault current, the driver is the overcurrent device rating. If it asks about the conductor to the electrode, the driver is the service conductor size. Say the driver out loud before opening either table.
Rounding up to the next standard overcurrent device rating on a multioutlet branch circuit that supplies receptacle outlets for cord-and-plug-connected portable loads, or rounding up past the small-conductor limits.
The next-size-up provision is remembered as a blanket permission and the listed conditions attached to it are forgotten.
What to do instead
Before rounding up, check that the circuit is not a multioutlet branch circuit feeding cord-and-plug portable loads, that the conductor ampacity does not already match a standard rating, that the next standard size does not exceed the 800 A ceiling, and that the small-conductor limits are still satisfied.
Limiting ground-fault circuit-interrupter protection to bathroom receptacles and missing kitchen countertops, laundry areas, garages, outdoors, unfinished basements, and receptacles near sinks; likewise assuming arc-fault protection applies only to bedroom outlets.
Study material is often organized around the room named in an older memory aid rather than the current list of locations and outlet types.
What to do instead
Build a location checklist from the code article itself for each occupancy and walk every question through the full list rather than stopping at the first location that matches. Treat AFCI and GFCI as separate lists and check each independently.
Ignoring ampacity adjustment for more than three current-carrying conductors in a raceway, or counting every neutral as a current-carrying conductor in a balanced multiwire branch circuit and over-adjusting.
Conduit fill and ampacity adjustment are treated as one topic, and the neutral-counting rules are more nuanced than the general adjustment rule.
What to do instead
Count current-carrying conductors first, apply the neutral rules only to the specific circuit type in the question, then apply the adjustment factor to the ampacity before any termination correction. Keep the adjustment step and the termination step as two separate lines of the calculation.
Using the motor nameplate current or the branch-circuit short-circuit and ground-fault protective device rating when selecting overload protection, or using the overload rating to size branch-circuit conductors.
Three different motor values (full-load current from the tables, branch-circuit protection, and overload protection) are learned together and swapped under time pressure.
What to do instead
Assign each motor value a job before computing: table full-load current drives conductor sizing, the short-circuit and ground-fault device protects the circuit, and the overload device protects the motor. Never let one value substitute for another in the next step.
Selecting conductor ampacity from the 90 degrees C column for the final termination on a 100 A-or-less circuit, or from the 60 degrees C column on a circuit above 100 A, without checking the termination rating.
The highest column gives the largest allowable ampacity and is chosen reflexively, and the temperature-correction and adjustment steps are done in the wrong order.
What to do instead
Set the rule on scratch paper: terminations of 100 A or less default to the 60 degrees C column unless the equipment is listed and identified otherwise, and terminations over 100 A use the 75 degrees C column. Use the higher column only for correction and adjustment calculations, then take the lower of the adjusted value and the termination-limited value.
Measuring working clearance depth from the wall or from the floor-mounted equipment front rather than from the live parts, and forgetting the required width and headroom.
Clearance is visualized as floor space in front of a panel instead of a defined volume measured from exposed live parts.
What to do instead
For every clearance question, first mark the live parts, then measure depth from them, add the required width around the equipment, and confirm the headroom. Check the dedicated equipment space above and below the equipment as a separate item.
Answering from habit, handbook commentary, or jobsite practice instead of the adopted code text, and assuming the current national edition applies without confirming the edition and state amendments in force.
Experienced candidates rely on how their jurisdiction used to inspect, and code editions change article numbering and requirements between cycles.
What to do instead
Before an exam sitting, confirm which edition and which state amendments are examinable, then practice every question as a text lookup exercise: find the article, read the actual requirement and its exceptions, and only then choose the answer.