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NEC code map — where every rule lives

The code book is on the screen, searchable, and not yours. Open book does not mean easy — it means the exam measures how fast you find a rule. At 2:42 a question, knowing which chapter owns the answer before you start searching is most of the job. That is what this page is.

2023 NEC · the edition the exam supplies

The nine chapters

  • Ch. 1 100–110 General Definitions (100) and requirements for installations (110). Article 90, the Introduction, sits outside Chapter 1 and carries the code arrangement rule. 110.14(C) terminations and 110.26 working space are two of the most-asked rules in the book.
  • Ch. 2 200–250 Wiring and protection Branch circuits (210), feeders (215), load calcs (220), services (230), overcurrent (240), grounding and bonding (250). Article 250 is the biggest fail area — navigate it by Part, not by searching.
  • Ch. 3 300–398 Wiring methods and materials General (300), conductors and ampacity (310), boxes (314), then the raceway and cable articles. Every one of those is laid out identically, so the pattern is worth more than the individual articles.
  • Ch. 4 400–490 Equipment for general use Cords (400), switches (404), receptacles (406), panelboards (408), luminaires (410), motors (430), transformers (450). Article 430 opens with a diagram at 430.1 that tells you which Part you need — use it every time.
  • Ch. 5 500–590 Special occupancies Hazardous locations (500–506), health care (517), agricultural (547), mobile homes (550), marinas (555), temporary installations (590).
  • Ch. 6 600–695 Special equipment Signs (600), elevators (620), EV supply (625), pools and spas (680), solar PV (690), fire pumps (695). Worth real time in California: 690 and 680 are everyday work here.
  • Ch. 7 700–770 Special conditions Emergency (700), legally required standby (701), optional standby (702), interconnected sources (705), energy storage (706), fire alarm (760). Know who classifies the load and how fast power must transfer — 700 vs 701 vs 702 is a favourite.
  • Ch. 8 800–840 Communications systems Stands alone. Chapters 1 through 7 do not apply here unless a Chapter 8 rule specifically says so. Do not carry a Chapter 3 rule into a Chapter 8 question.
  • Ch. 9 Tables Tables and annexes Table 1 fill percentages, Table 4 raceway areas, Table 5 conductor areas, Table 8 conductor properties. Annex C is the biggest time-saver in the book: same-size conductors, one lookup.

Which table takes which input

Most wrong answers on the calculation half of the exam come from using the right method with the wrong table. Table 250.66 and Table 250.122 are the pair people confuse most — one takes the service conductor size, the other takes the overcurrent device rating.

  • Table 310.16 TakesConductor size, insulation temperature rating GivesAmpacity for up to three current-carrying conductors at 30 °C
  • 310.15(B) TakesActual ambient temperature GivesThe correction factor — step two of every ampacity problem
  • 310.15(C)(1) TakesNumber of current-carrying conductors GivesThe adjustment factor above three. Missing the double derate is the classic wrong answer
  • 110.14(C) TakesCircuit rating, and any equipment marking Gives60 °C at 100 A and below, 75 °C above — the cap on your final answer
  • 240.4(D) TakesConductor size, 14 / 12 / 10 AWG GivesThe small-conductor overcurrent ceiling, overriding the ampacity you calculated
  • Table 240.6(A) TakesA calculated current GivesThe standard device rating to round to. Memorise through 100 A
  • Table 250.66 TakesThe largest ungrounded service conductor GivesGrounding electrode conductor size
  • Table 250.122 TakesThe overcurrent device rating GivesEquipment grounding conductor size. Different input entirely — this is the pair people confuse
  • 314.16(A) / (B) TakesBox dimensions, then what goes in it GivesBox volume, then the volume allowance per conductor. A two-part lookup
  • Table 430.248 / .250 TakesHorsepower and voltage GivesMotor full-load current for conductor and OCPD sizing — never the nameplate
  • Table 430.52 TakesMotor type and protective device type GivesMaximum branch-circuit protection percentage. Fuses and breakers differ
  • Table 450.3(A) / (B) TakesTransformer voltage class, primary only or primary and secondary GivesOvercurrent protection percentages
  • Table 300.5 TakesWiring method and what is above it GivesMinimum burial depth. Easy points
  • Table 110.26(A)(1) TakesVoltage to ground and the condition GivesWorking space depth. Know what makes a space Condition 1, 2 or 3

Four procedures worth running on autopilot

Each of these is an ordered sequence, and each has one step people skip. Doing them out of sequence produces a plausible wrong answer — which is usually one of the four options.

Conductor ampacity

310.16 → 310.15(B) → 310.15(C)(1) → 110.14(C) → 240.4(D)

  1. 1 Start in Table 310.16, in the column for the conductor’s own insulation rating — usually 90 °C.
  2. 2 Correct for ambient temperature if it is not 30 °C.
  3. 3 Adjust for more than three current-carrying conductors in the raceway or cable.
  4. 4 Compare against the termination rating — 60 °C or 75 °C. The final ampacity cannot exceed that column.
  5. 5 Apply the small-conductor rule for 14, 12 and 10 AWG.

The trapYou derate from 90 °C but you terminate at 75 °C. Both apply. Skipping either one is the trap.

Motor branch circuit

430.6 → 430.22 → 430.32 → 430.52 → 250.122

  1. 1 Look up full-load current in Table 430.248 or 430.250, by horsepower and voltage.
  2. 2 Size conductors at 125% of that table FLC.
  3. 3 Size overload protection from the nameplate FLA — the one step that uses the nameplate.
  4. 4 Size short-circuit and ground-fault protection by the percentage in Table 430.52 for your device type.
  5. 5 Round up where the exception permits, then size the EGC from Table 250.122.

The trapTable FLC for the conductors and the breaker. Nameplate FLA for the overload. Mixing them is the most common motor mistake.

Box fill

314.16(A) and 314.16(B)

  1. 1 Count each conductor entering and terminating, or passing through — one volume each.
  2. 2 All internal clamps together count as one, based on the largest conductor.
  3. 3 Each luminaire stud or hickey counts as one.
  4. 4 Each yoke or strap counts as two, based on the largest conductor connected to it.
  5. 5 Equipment grounding conductors: one allowance for up to four, then a quarter each beyond.

The trapPigtails that begin and end inside the box count for nothing. Neither do fittings entering the box.

Conduit fill

Chapter 9 Tables 1, 4 and 5 — or Annex C

  1. 1 If every conductor is the same size and type, go straight to Annex C and stop. One lookup.
  2. 2 Otherwise take the fill percentage from Table 1 — 53% for one conductor, 31% for two, 40% for more than two.
  3. 3 Get each conductor’s area from Table 5 and total them.
  4. 4 Find the raceway whose allowable area in Table 4 exceeds that total.

The trapThe percentage depends on the number of conductors, and two is the most restrictive case at 31%.

Worth memorising

The formulas are not in the on-screen references. This is the part of the exam that genuinely tests recall rather than lookup, which makes it the highest-value thing to carry in.

Ohm’s law and power

E = I × R

P = I × E

P = I² × R

Three-phase

VA = E × I × 1.732

I = VA ÷ (E × 1.732)

1.732 is √3 — it is in nearly every three-phase question.

Voltage drop

VD = (2 × K × I × L) ÷ CM

Three-phase: swap the 2 for 1.732. K ≈ 12.9 copper, 21.2 aluminium. Circular mils from Chapter 9 Table 8.

Wye

E line = 1.732 × E phase

I line = I phase

Delta

E line = E phase

I line = 1.732 × I phase

Wye multiplies voltage, delta multiplies current. Backwards is a designed-in wrong answer.

Continuous load

Size at 125%

Load ≤ 80% of rating

Three hours or more. The same rule stated two ways — a question may use either.

Transformer ratio

Ep ÷ Es = Np ÷ Ns = Is ÷ Ip

Current is inverse to voltage. Note the flipped subscripts.

Power factor and efficiency

PF = W ÷ VA

Eff = P out ÷ P in

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Written by Chris Furman · last reviewed September 2026

I built Electrician Cards after watching a friend prepare for this exam and discovering how much of the published advice is written for a closed-book test. I am not an electrician — everything here is researched from the candidate bulletin, the 2023 NEC's own structure, and the official content outline, and it is checked against them again whenever it changes. Always verify against the code book itself.