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 = 4.2A1.5 HP = 6.0A2 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
- • All kitchen receptacles (210.8(A)(6), NEC 2023 expansion)
- • 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, NEC 2023 requires GFCI for ALL kitchen receptacles (not just countertop outlets), and 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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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