NEC Quick Reference
NEC Key Numbers Cheat Sheet
The essential numbers, rules, and multipliers every electrician needs for the licensing exam. Bookmark this page or print it for open-book reference.
Wire Sizing — Table 310.16 (Copper, 60°C/75°C)
| AWG | 60°C Ampacity | 75°C Ampacity | Common Use |
|---|---|---|---|
| #14 | 15A | 20A | General lighting/receptacles (240.4(D): 15A max) |
| #12 | 20A | 25A | Kitchen/bath/garage (240.4(D): 20A max) |
| #10 | 30A | 35A | Dryer, A/C, water heater |
| #8 | 40A | 50A | Range, large A/C |
| #6 | 55A | 65A | Sub-panels, large appliances |
| #4 | 70A | 85A | Service feeders |
| #3 | 85A | 100A | Service feeders |
| #2 | 95A | 115A | Service feeders |
| #1 | 110A | 130A | Service feeders |
| #1/0 | 125A | 150A | 100–150A services |
| #2/0 | 145A | 175A | 150–200A services |
| #3/0 | 165A | 200A | 200A services |
| #4/0 | 195A | 230A | 200–225A services |
| 250 kcmil | 215A | 255A | Large services/feeders |
| 350 kcmil | 260A | 310A | Large services/feeders |
| 500 kcmil | 320A | 380A | Large services/feeders |
* 240.4(D): #14 max 15A, #12 max 20A, #10 max 30A for branch circuit protection. NM-B cable uses 60°C column even though conductors are rated 90°C.
Full Table 310.16 guide with correction/adjustment factors →
Standard OCPD Ratings — NEC 240.6(A)
15A20A25A30A35A40A45A50A60A70A80A90A100A110A125A150A175A200A225A250A300A350A400A450A500A600A700A800A1000A1200A1600A2000A2500A3000A4000A5000A6000A
Next-size-up rule (240.4(B)):When the calculated ampacity doesn't match a standard rating, use the next higher standard size — but only if the conductor is not part of a multi-outlet branch circuit supplying receptacles for cord-and-plug connected loads.
Working Space Clearances — Table 110.26(A)(1)
| Condition | 0–150V | 151–600V | Description |
|---|---|---|---|
| 1 | 3 ft | 3 ft | Exposed live parts on one side only, grounded or no live parts on other side |
| 2 | 3 ft | 3½ ft | Exposed live parts on one side, grounded parts (concrete, brick, tile) on other side |
| 3 | 3 ft | 4 ft | Exposed live parts on both sides of the working space |
Other 110.26 Requirements
- • Width: 30 in. or equipment width (whichever is greater)
- • Headroom: 6½ ft minimum (or equipment height if greater)
- • Illumination required for all indoor working spaces
- • Dedicated equipment space: 6 ft wide × depth of panel above panel, to ceiling or 25 ft (whichever is less)
Exam Tips
- • Condition 1 is the most common: 3 ft minimum for both voltage ranges
- • Condition 3 is the most dangerous: exposed live parts on both sides
- • Know all three conditions for 151–600V (3/3.5/4 ft)
Motor Circuit Rules — Article 430
| Component | Multiplier | NEC Reference | Notes |
|---|---|---|---|
| Branch circuit conductors | 125% of motor FLA | 430.22 | Size wire for 125% of nameplate FLA (or Table 430.250) |
| Overload protection (SF ≥ 1.15 or temp rise ≤ 40°C) | 125% of FLA | 430.32(A)(1) | Most common motors |
| Overload protection (all other motors) | 115% of FLA | 430.32(A)(1) | Unlabeled SF or temp rise > 40°C |
| SCGF — Inverse time breaker | 250% of FLA | Table 430.52 | Max setting (can go up to 400% if needed to start) |
| SCGF — Dual element fuse | 175% of FLA | Table 430.52 | Max setting |
| SCGF — Instantaneous trip CB | 800% of FLA | Table 430.52 | For motor circuit protectors |
| Disconnect rating | 115% of FLA | 430.110 | Minimum disconnect ampere rating |
| Feeder conductors (2+ motors) | 125% of largest + sum of rest | 430.24 | Size for largest motor at 125% |
Motor FLA Quick Reference (3-phase, 230V — Table 430.250)
1 HP = 3.6A1.5 HP = 5.2A2 HP = 6.8A3 HP = 9.6A5 HP = 15.2A7.5 HP = 22A10 HP = 28A15 HP = 42A20 HP = 54A25 HP = 68A30 HP = 80A50 HP = 130A
Box Fill — NEC 314.16
| Item | Volume Count | Volume per Conductor |
|---|---|---|
| Each unbroken conductor passing through | 1 conductor | Per wire gauge below |
| Each conductor entering and terminating | 1 conductor | Per wire gauge below |
| Largest ungrounded conductor for devices (per strap) | 2 conductors | Per wire gauge below |
| Equipment grounding conductors (all combined) | 1 conductor | Largest EGC in box |
| Clamps (all internal clamps combined) | 1 conductor | Largest conductor in box |
| Fixture studs / hickeys | 1 conductor each | Largest conductor in box |
| Wire Size | Volume per Conductor |
|---|---|
| #18 AWG | 24.6 mL (1.50 in³) |
| #16 AWG | 28.7 mL (1.75 in³) |
| #14 AWG | 32.8 mL (2.00 in³) |
| #12 AWG | 36.9 mL (2.25 in³) |
| #10 AWG | 41.0 mL (2.50 in³) |
| #8 AWG | 49.2 mL (3.00 in³) |
| #6 AWG | 81.9 mL (5.00 in³) |
Minimum Burial Depths — Table 300.5
| Wiring Method | General (not under building) | Under 2" concrete slab | Under street/highway | Under 1-2 family driveway |
|---|---|---|---|---|
| Direct-buried conductors (UF cable) | 24 in. | 18 in. | 24 in. | 18 in. |
| Rigid nonmetallic conduit (Schedule 40/80 PVC) | 18 in. | 12 in. | 24 in. | 18 in. |
| Rigid metal conduit / IMC | 6 in. | 6 in. | 24 in. | 6 in. |
| EMT | 18 in. | 12 in. | 24 in. | 18 in. |
| GFCI-protected / 120V or less | 12 in. | 6 in. | 24 in. | 12 in. |
Key: RMC/IMC gets 6 inches everywhere (except streets). PVC gets 18 inches general. Direct bury gets 24 inches general.
Service Drop Overhead Clearances — 230.24
| Location | Minimum Clearance |
|---|---|
| Above flat roofs (slope < 4/12) | 8 ft |
| Above roofs with slope ≥ 4/12 | 3 ft |
| Above roofs — final 4 ft to weatherhead | 18 in. |
| Above sidewalks and areas accessible to pedestrians only | 10 ft |
| Above residential driveways and commercial lots not subject to trucks | 12 ft |
| Above roads, streets, alleys, driveways accessible to trucks | 18 ft |
| Above windows/doors/porches (horizontal distance) | 3 ft |
| Above ground — initial attachment point at building | 10 ft (min) |
GFCI & AFCI Required Locations — 210.8 & 210.12
GFCI Required (210.8) — Dwelling Units
- • Bathrooms
- • Garages and accessory buildings with a floor at grade
- • Outdoors (all outdoor receptacles)
- • Crawl spaces (at or below grade)
- • Unfinished basements
- • Kitchen countertop receptacles (within 6 ft of sink)
- • Sinks in other locations (within 6 ft)
- • Boathouses
- • Bathtubs/shower stalls (within 6 ft)
- • Laundry areas
- • Indoor wet bar sinks (within 6 ft)
AFCI Required (210.12) — Dwelling Units
- • All 120V, 15A and 20A branch circuits supplying outlets in:
- – Bedrooms
- – Living rooms, parlors, libraries, dens
- – Sunrooms, recreation rooms, closets, hallways
- – Kitchens, laundry areas, dining rooms
- – All other rooms in a dwelling unit
- • Dormitory units
- • Guest rooms and suites of hotels/motels
Exam tip: GFCI is location-based (near water/grade/outdoors). AFCI is circuit-based (120V 15/20A circuits in living spaces). Both are required in kitchens — GFCI for countertop receptacles within 6 ft of sink, AFCI for the entire kitchen circuit.
Key Electrical Formulas
Ohm's Law
V = I × R
I = V ÷ R
R = V ÷ I
Power (Watts)
P = V × I
P = I² × R
P = V² ÷ R
Voltage Drop (single phase)
VD = 2 × K × I × D ÷ CM
K = 12.9 (copper), 21.2 (aluminum)
CM = conductor circular mils
NEC recommendation: ≤ 3% feeder, ≤ 5% total
Three-Phase Power
P = √3 × V × I × PF
I = VA ÷ (√3 × V)
√3 ≈ 1.732
Transformer
V₁ ÷ V₂ = N₁ ÷ N₂ = I₂ ÷ I₁
kVA = V × I ÷ 1000 (single phase)
kVA = √3 × V × I ÷ 1000 (three phase)
Continuous Load Rule (210.19)
Min ampacity = (continuous load × 1.25) + non-continuous load
Continuous = energized ≥ 3 hours
Wiring Method Support Intervals
| Wiring Method | Max Support Interval | Near Boxes/Fittings | NEC Reference |
|---|---|---|---|
| NM cable (Romex) | 4½ ft (54 in.) | 12 in. | 334.30 |
| AC cable (armored cable) | 4½ ft (54 in.) | 12 in. | 320.30 |
| MC cable (metal-clad) | 6 ft | 12 in. | 330.30 |
| EMT (conduit) | 10 ft | 3 ft from box | 358.30 |
| Rigid metal conduit (RMC) | 10 ft | 3 ft from box | 344.30 |
| Rigid PVC conduit | Per Table 352.30(B) | 3 ft from box | 352.30 |
| FMC (flexible metal conduit) | 4½ ft | 12 in. | 348.30 |
| LFMC | 4½ ft | 12 in. | 350.30 |
| ENT (smurf tube) | 3 ft | 3 ft from box | 362.30 |
| Wireways | 5 ft | — | 376.30 |
PVC conduit support spacing varies by trade size and temperature — see Table 352.30(B). Expansion fittings required in long runs.
Key Service Rules — Article 230
Max service disconnects per service6 (230.71)
Min service for 1-family dwelling100A (230.79(C))
Min service — all other60A (230.79(A))
Service under 2 in. concrete = outside building230.6
POCO clearance (above roof, flat)8 ft (230.24)
POCO clearance (≥4/12 slope)3 ft (230.24)
Drip loop — min height at building10 ft (230.54)
Disconnect locationReadily accessible, nearest point of entry (230.70)
Put These Numbers to Work
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Try Free Practice QuestionsDeep-Dive Article Guides
NEC Article 110NEC Article 210 — Branch CircuitsNEC Article 220 — Load CalculationsNEC Article 230 — ServicesNEC Article 240 — Overcurrent ProtectionNEC Article 250 — Grounding & BondingNEC Article 300 — Wiring MethodsNEC Article 334 — NM Cable (Romex)NEC Article 430 — MotorsNEC Articles 404 & 406 — Switches & ReceptaclesTable 310.16 — Wire Sizing & AmpacityChapter 9 — Conduit Fill