Electrical Trade Knowledge (Journeyman Electrician)
What the journeyman exam actually tests
The journeyman exam rewards a working command of Ohm's law and the power relationships, series/parallel circuit behavior, conductor and overcurrent sizing, grounding and bonding, and safe work practices. You should be able to move fluidly between volts, amps, ohms, and watts, compute voltage drop, and read a panel schedule or one-line diagram without hesitation.
Concepts to master
- Circuit fundamentals: series current is common, parallel voltage is common; total resistance of parallel branches uses reciprocals.
- Power: P = VI = I²R = V²/R. Single-phase vs. three-phase (P = √3 × V × I × PF) trips up many candidates.
- Conductor and OCPD sizing: continuous loads at 125%, standard OCPD ratings, ampacity tables with adjustment and correction factors.
- Grounding vs. bonding: these are not synonyms; equipment grounding conductors clear faults, grounding electrodes stabilize voltage.
- Motors and transformers: overload vs. short-circuit protection are separate functions.
Traps to expect
Questions often supply extra data to see if you pick the right formula, mix continuous and noncontinuous loads, or confuse ampacity with overcurrent rating. Watch for "minimum" versus "maximum" wording, and remember that voltage drop is a design recommendation, not a code maximum, in most cases. Unit conversions (kVA to VA, milliamps to amps) are common distractors.
Worked example
A 240 V single-phase branch carries a 30 A continuous load. Minimum conductor ampacity = 30 × 1.25 = 37.5 A, so select a conductor with at least 37.5 A ampacity and an OCPD rated at least 37.5 A (next standard size up if needed). If the run is 150 ft of 8 AWG copper (about 0.778 ohms/1000 ft), voltage drop ≈ 2 × 150/1000 × 0.778 × 30 ≈ 7.0 V, or about 2.9% - a useful sanity check.
Rule of thumb
For quick single-phase drop estimates, VD ≈ (2 × K × I × L)/CM with K ≈ 12.9 for copper.