Journeyman Exam Prep — NEC Calculations
The journeyman exam is the gateway to real money. This lesson covers the calculation categories the exam emphasizes — service calcs, conduit fill, motor circuits, and voltage drop — with worked examples.
The lesson
Service load calculation — standard method
NEC 220.40-220.43. For a 2400 sq ft home: 3 VA × 2400 = 7200 VA general lighting. Add 1500 × 2 = 3000 VA small appliance, 1500 VA laundry. First 3000 VA at 100%, remainder at 35%: 3000 + (8700 × 0.35) = 3000 + 3045 = 6045 VA general. Add appliances at nameplate: dryer 5500 VA, range 8000 VA (use Table 220.55 for derating on ranges), HVAC 7000 VA. Total ÷ 240 = service amps. Calculate every house — it's exam GOLD.
Optional method (NEC 220.82)
Quicker for residential. First 10 kVA at 100%, remainder at 40%. Plus 100% of HVAC. Plus 100% of fixed appliances. Often gives a smaller service size than standard — both methods are valid; calculate both, use the smaller (legally). Memorize the formula structure. Exam will give you a house + appliances + ask 'what's the minimum service size?'
Conduit fill — Table 4 + Chapter 9
Conduit fill percentages: 1 conductor — 53%; 2 conductors — 31%; 3+ conductors — 40%. Look up the conductor cross-sectional area in Table 5, multiply by count, divide by conduit interior area in Table 4. Example: 6 × #12 THHN in 3/4" EMT — each #12 THHN = 0.0133 in², total = 0.0798 in², 3/4" EMT max 40% = 0.213 in². OK. Conduit fill problems are exam staples — practice many.
Motor circuit sizing — NEC 430
Branch circuit conductors: 125% of motor FLC (full-load current). Overcurrent protection: 150–300% of FLC depending on motor type (inverse time breaker — 250% for typical 3-phase). Overload protection: 115–125% of FLC (separate from branch protection). Disconnect required in sight of motor. Motor calcs feel complex; they follow a strict formula — memorize the steps.
Voltage drop — Chapter 9 Table 9 or formula
VD = 2 × K × I × D ÷ CM (single phase). K = 12.9 for copper, 21.2 for aluminum (at 75°C). I = current. D = one-way distance. CM = circular mils of conductor (Table 8). Max recommended drop: 3% on branch, 5% total. Long runs (200 ft+) of #12 at 16A often violate this. Upsize to #10 to comply. Exam will give you a current + distance + asks for minimum conductor.
Test-taking strategy
Memorize structure of common calculations — don't try to derive in the exam. Use Mike Holt practice tests + state-specific prep. Time pressure is real: 80 questions in 4 hours = 3 min per question. Skip hard ones, answer easy first. Most jurisdictions require 70% to pass; pass rate first attempt is around 50–60%. Study at least 80 hours. Pass on first try saves $200 retake fee + weeks of waiting for the next slot.
Tool list
- NEC 2023 (or applicable cycle for your state)
- Mike Holt Journeyman Exam Prep set (book + practice tests + videos)
- State-specific exam prep (each state has slightly different scope)
- Calculator allowed by your jurisdiction (most allow basic non-programmable)
- Approved exam center reservation booked WELL in advance
- Pre-exam mental fitness — sleep, hydration, food. Do NOT cram.
Safety — Read or get hurt
- !!Carrying an unapproved calculator into the exam = disqualification.
- !!Lying on the application about prior work history = disqualification + ban.
- !!Cheating gets you blacklisted from electrical work statewide; not worth it.
Take the mini quiz
6 questions · pass at 80%