Journeyman Electrician Exam-Day Cheat Sheet
High-yield reference matrices, critical rules, classification charts, and formula cheat sheets for the Journeyman Electrician Exam (NEC / NFPA 70).
📌 Quick Summary / Core Test Principles:NEC Quick Reference: Continuous Load = Noncontinuous + 125% continuous load (NEC 210.19). Conductor Ampacity: 75°C terminal rating governs equipment terminations <= 100A / 14-1 AWG unless listed otherwise (NEC 110.14(C)). Grounding: Table 250.66 sizes Grounding Electrode Conductor based on largest ungrounded service conductor. Table 250.122 sizes Equipment Grounding Conductor based on upstream OCPD rating. Motors: Branch circuit conductor sized at 125% of motor Full Load Current (FLC from Tables 430.248/250, NOT nameplate). Inverse time circuit breaker OCPD max rating = 250% FLC (NEC Table 430.52). Conduit Fill: 1 conductor = 53%, 2 conductors = 31%, 3+ conductors = 40% (Chapter 9, Table 1).
Conductor Sizing
NEC Table 310.16 Allowable Ampacities of Insulated Conductors (Copper)
| Conductor Size (AWG/kcmil) | 60°C (TW, UF) | 75°C (THWN, XHHW) | 90°C (THHN, XHHW-2) | Standard Overcurrent Protection |
|---|---|---|---|---|
| 14 AWG | 15 A | 20 A | 25 A | 15 A (NEC 240.4(D)) |
| 12 AWG | 20 A | 25 A | 30 A | 20 A (NEC 240.4(D)) |
| 10 AWG | 30 A | 35 A | 40 A | 30 A (NEC 240.4(D)) |
| 8 AWG | 40 A | 50 A | 55 A | 40 A (60°C) / 50 A (75°C) |
| 6 AWG | 55 A | 65 A | 75 A | 60 A (75°C) |
| 4 AWG | 70 A | 85 A | 95 A | 70 A (60°C) / 85 A (75°C) |
| 2 AWG | 95 A | 115 A | 130 A | 100 A (60°C) / 115 A (75°C) |
| 1/0 AWG | 125 A | 150 A | 170 A | 125 A (60°C) / 150 A (75°C) |
| 2/0 AWG | 145 A | 175 A | 195 A | 175 A (75°C) |
| 4/0 AWG | 195 A | 230 A | 260 A | 200 A (60°C) / 225 A (75°C) |
💡 Pro Tip:Terminations on equipment rated 100A or less default to 60°C ampacity unless explicitly marked for 75°C (NEC 110.14(C)(1)(a)).
Grounding Standards
NEC Table 250.66 Grounding Electrode Conductor (GEC) Sizing Matrix
| Largest Service Conductor (Copper) | Largest Service Conductor (Aluminum) | GEC Size (Copper) | GEC Size (Aluminum) |
|---|---|---|---|
| 2 AWG or smaller | 1/0 AWG or smaller | 8 AWG | 6 AWG |
| 1 AWG or 1/0 AWG | 2/0 or 3/0 AWG | 6 AWG | 4 AWG |
| 2/0 or 3/0 AWG | 4/0 AWG or 250 kcmil | 4 AWG | 2 AWG |
| Over 3/0 thru 350 kcmil | Over 250 thru 500 kcmil | 2 AWG | 1/0 AWG |
| Over 350 thru 600 kcmil | Over 500 thru 900 kcmil | 1/0 AWG | 3/0 AWG |
| Over 600 thru 1100 kcmil | Over 900 thru 1750 kcmil | 2/0 AWG | 4/0 AWG |
| Over 1100 kcmil | Over 1750 kcmil | 3/0 AWG | 250 kcmil |
💡 Pro Tip:Special caps apply: Ground rod sole connection max 6 AWG Cu (250.66(A)); Concrete-encased Ufer ground sole connection max 4 AWG Cu (250.66(B)); Ground ring max 2 AWG Cu (250.66(C)).
Equipment Grounding
NEC Table 250.122 Equipment Grounding Conductor (EGC) Sizing
| Overcurrent Device Rating (Amperes) | Copper Conductor Size (AWG) | Aluminum Conductor Size (AWG) | Proportional Upsizing Rule |
|---|---|---|---|
| 15 A | 14 AWG | 12 AWG | Mandatory proportional increase if ungrounded conductors upsized |
| 20 A | 12 AWG | 10 AWG | EGC must be increased in circular mils ratio per NEC 250.122(B) |
| 30 A | 10 AWG | 8 AWG | Applicable when conductors are upsized for voltage drop |
| 40 A / 60 A | 10 AWG | 8 AWG | Table 250.122 establishes minimum cross-sectional area |
| 100 A | 8 AWG | 6 AWG | Bonding bushings required for service raceways |
| 200 A | 6 AWG | 4 AWG | Raceway cannot serve as EGC if ground continuity broken |
| 400 A | 3 AWG | 1 AWG | Multiple parallel raceways require full-size EGC in each conduit |
💡 Pro Tip:When conductors are increased in size for voltage drop, the EGC must be increased proportionately in circular mil area (NEC 250.122(B)).
Conduit & Raceways
NEC Chapter 9 Table 1 Conduit Fill Allowable Percentages
| Number of Conductors in Raceway | Maximum Cross-Sectional Fill (%) | Applicable Conduit Types | Common Code Application |
|---|---|---|---|
| 1 Conductor | 53% | EMT, RMC, IMC, PVC (Sch 40/80) | Single ground wire or heavy lead feeder |
| 2 Conductors | 31% | EMT, RMC, IMC, PVC (Sch 40/80) | Two-wire branch circuits or single-phase runs without ground |
| Over 2 Conductors (3+) | 40% | EMT, RMC, IMC, PVC (Sch 40/80) | Standard 3-wire and 4-wire multiwire branch circuits and feeders |
| Nipple <= 24 Inches (600 mm) | 60% | All approved raceway nipples | No derating required per Note 4 to Chapter 9 tables |
| Cable with Elliptical Cross-Section | Based on major diameter | All approved raceways | Treated as single round cable using largest diameter dimension |
💡 Pro Tip:Conduit nipples 24 inches or less can be filled to 60% and do NOT require ampacity adjustment derating (Chapter 9, Note 4).
Box Fill Calculations
NEC Table 314.16(B) Volume Allowance Required per Conductor
| Conductor Size (AWG) | Free Space Required per Conductor (cu in) | Device Allowance Factor | Ground Conductor Factor |
|---|---|---|---|
| 18 AWG | 1.50 cu. in. | Double volume allowance (2x) | Single volume for up to 4 grounds; 1/4 volume per ground thereafter |
| 16 AWG | 1.75 cu. in. | Double volume allowance (2x) | Single volume for up to 4 grounds; 1/4 volume per ground thereafter |
| 14 AWG | 2.00 cu. in. | 4.00 cu. in. per switch/receptacle yoke | 2.00 cu. in. for all EGCs combined (up to 4) |
| 12 AWG | 2.25 cu. in. | 4.50 cu. in. per switch/receptacle yoke | 2.25 cu. in. for all EGCs combined (up to 4) |
| 10 AWG | 2.50 cu. in. | 5.00 cu. in. per switch/receptacle yoke | 2.50 cu. in. for all EGCs combined (up to 4) |
| 8 AWG | 3.00 cu. in. | 6.00 cu. in. per switch/receptacle yoke | 3.00 cu. in. for all EGCs combined (up to 4) |
| 6 AWG | 5.00 cu. in. | 10.00 cu. in. per switch/receptacle yoke | 5.00 cu. in. for all EGCs combined (up to 4) |
💡 Pro Tip:One or more internal cable clamps count as ONE conductor volume based on the largest conductor in the box (NEC 314.16(B)(2)).
Motor Branch Circuits
NEC Table 430.52 Maximum Rating of Motor Branch-Circuit Protection
| Motor Type | Nontime-Delay Fuse | Dual-Element Time-Delay Fuse | Inverse-Time Circuit Breaker |
|---|---|---|---|
| Single-Phase Motors | 300% | 175% | 250% |
| AC Polyphase Squirrel-Cage (Normal) | 300% | 175% | 250% |
| Design B Energy-Efficient Motors | 300% | 175% | 250% |
| Wound Rotor AC Motors | 150% | 150% | 150% |
| Direct-Current (DC) Motors | 150% | 150% | 150% |
💡 Pro Tip:If the calculated breaker percentage does not correspond to a standard rating in 240.6, the NEXT HIGHER standard rating is permitted (NEC 430.52(C)(1) Ex. 1).