Craftsman Electricity common mistakes
Craftsman Electricity · Understand the traps and how to avoid them.
When sizing a service or feeder, the candidate adds the general lighting load, small-appliance and laundry branch circuits, and the range/dryer demand factors as if all applied at 100%, then selects a conductor from that inflated total.
The demand-factor tables and the optional versus standard calculation methods are similar in structure, so candidates memorize one table but forget that the standard method applies the general lighting demand factor to the first 3 VA/ft² block and then a different factor above it, and that the neutral load is calculated separately from the ungrounded conductors.
What to do instead
Work every service calculation on a worksheet with a dedicated line for each step: general lighting VA, small-appliance and laundry, appliance demand factors, range and dryer columns, largest motor at 125%, then the neutral calculation. Before answering, label which method (standard or optional) the question invokes and confirm every demand factor was pulled from the correct column.
The candidate treats the equipment grounding conductor and the grounded (neutral) conductor as interchangeable, bonding the neutral to the enclosure at a subpanel or sizing the EGC from the neutral table.
The two conductors are both often white or bare in the field, and candidates conflate 'grounding' with 'bonding'. The rule that the service disconnect is the only point where neutral and equipment ground are bonded is easy to state but easy to misapply in a question about a detached building or a separately derived system.
What to do instead
Drill the distinction: the grounded conductor carries normal return current; the equipment grounding conductor carries fault current only. Memorize the locations where main bonding jumpers are required (service disconnect, separately derived source) and where they must be absent (load-side panels, subpanels, detached structures with their own grounding electrode). Practice reading one-line diagrams and circling every bonding point.
On box-fill and conduit-fill questions, the candidate counts only the visible conductors and ignores the clamps, support fittings, device yokes, and equipment grounding conductors, or forgets the free-space allowance for the box volume.
The tables are memorized in isolation, so the candidate remembers the cubic-inch volume per conductor but not the additional volume allowances that must be added before dividing. Raceway fill questions trip candidates because they apply the 40% rule to a nipple or use the wrong chapter for the conductor type.
What to do instead
Build a fixed checklist: count current-carrying and grounded conductors, add one allowance per clamp, one per support fitting, one or more per device yoke, and one for all EGCs combined. Then look up the box volume from the box table and divide. For conduit, identify whether the run is a nipple (60% fill) or a normal raceway (40%), and confirm the conductor dimension comes from the correct insulation column.
The candidate answers motor branch-circuit and overload questions using the nameplate full-load current and applies the same percentage to both the branch-circuit short-circuit and ground-fault protection and the overload device.
Motor questions mix three different currents (nameplate FLC, table FLC, and actual running current) and two different protection functions, and candidates treat 125% as a universal multiplier. They also forget that the overload device is sized to the nameplate current while the branch-circuit protection is sized to the table value.
What to do instead
Separate the two calculations on paper: branch-circuit conductor and short-circuit protection use the table FLC times the applicable percentage; overload protection uses the nameplate current with the permitted increase if the device will not hold. Memorize the standard overload percentages and the rule allowing the next larger device when the calculated value does not correspond to a standard size. Practice with a motor schedule until the two columns never blur.
The candidate sizes a transformer primary or secondary conductor, or its overcurrent protection, from the kVA rating alone without applying the primary and secondary protection percentages and the next-standard-size rule, and forgets the ampacity adjustment for the secondary conductors.
Transformer questions look like simple Ohm's-law problems, so candidates compute the current and stop. The protection percentages, the allowance for the next higher standard device, and the distinction between protected-at-primary-only and protected-at-both-ends configurations are the parts that actually get tested.
What to do instead
Use a three-line template for every transformer problem: full-load current on each side from kVA and voltage, conductor ampacity with any adjustment factors, then the overcurrent device from the protection table with the next-standard-size check. Explicitly note whether the transformer is a dry type or liquid filled and whether primary-only protection is permitted for the application.
The candidate applies the general receptacle-spacing rule to every room and misses the exceptions for small-appliance countertops, islands, peninsulas, and the specific distance measured along the floor line versus the wall line.
Branch-circuit receptacle spacing questions hinge on where the measurement starts and stops, and candidates picture the room rather than the rule. Kitchen and bathroom requirements differ in GFCI scope, circuit size, and whether the receptacle can serve other outlets, and those differences get blended together.
What to do instead
Draw a simple floor plan for each practice question and mark the measured wall segments, including breaks at doorways and appliances. Keep a one-page comparison of kitchen, bathroom, laundry, garage, and outdoor receptacle rules covering GFCI, circuit size, and dedicated-circuit requirements. Verify which rooms the spacing rule actually covers before applying it.
When troubleshooting a circuit, the candidate jumps to replacing a component (breaker, motor, contactor) based on the symptom rather than measuring voltage at each point to localize the fault, and does not isolate the circuit before resistance testing.
Symptom-to-part shortcuts feel efficient under time pressure, and candidates lack a disciplined sequence for separating an open circuit from a short or a high-resistance connection. They also forget that a resistance reading taken with the circuit energized is meaningless and dangerous.
What to do instead
Adopt a fixed sequence: verify supply voltage at the source, then at each device in order, using a known-good meter and a live-dead-live check. For opens, measure voltage across suspected breaks with the load connected; for shorts, isolate and measure resistance to ground. State the expected reading before each measurement so an unexpected value is caught immediately.
The candidate confuses the working-space clearance and dedicated-equipment space rules with the general clearance-from-building rules, and applies a single number to panels, switchgear, and overhead lines alike.
Several clearance tables use similar-looking numbers for different conditions, and candidates memorize one figure without the conditional column (voltage to ground, live parts on one side versus both, presence of insulating barriers). Overhead line clearances add another layer because they depend on voltage and on whether the conductor is insulated.
What to do instead
Learn each clearance table by its condition columns, not by a single number. Sketch the panel elevation for working-space questions and mark which side has live parts. For overhead lines, note the voltage class and insulation status before selecting the distance. Re-derive the number from the table during practice rather than recalling it.
The candidate applies lockout/tagout and energized-work rules as a single step ('lock the disconnect') and omits verification of the absence of voltage, the try-step, and the boundary distances that determine what PPE and approach are permitted.
Safety questions reward procedural completeness, but candidates compress the sequence into the one action they remember. The approach boundaries and PPE categories are numeric and easy to mix up, especially when the question changes the voltage or the available fault current.
What to do instead
Memorize the lockout sequence as an ordered list: notify, shut down, isolate, apply lock and tag, release stored energy, verify absence of voltage with a tested meter, then try the start. For approach boundaries, practice selecting the limited, restricted, and arc-flash boundaries from the voltage and the incident-energy label, and match the PPE category to the label rather than to habit.
The candidate treats a control circuit as if it followed the same rules as the power circuit, sizing control conductors and overcurrent protection from the motor branch-circuit values and ignoring the control transformer's primary and secondary protection.
Control schematics are read as logic diagrams, so candidates trace the sequence correctly but never ask what protects the control circuit. The control transformer's inrush and the permitted primary protection sizing are a frequent blind spot, as is the requirement that the control circuit be protected against overcurrent.
What to do instead
For every control question, redraw the power circuit and the control circuit as two separate one-lines, then apply the control-circuit protection rules to the transformer primary and secondary independently. Note the inrush allowance for the primary device and the conductor sizing rule for control wiring. Trace the ladder from the source through each device and label the voltage at each node before answering.