NEC Quick Reference Guide
Quick reference to common National Electrical Code (NEC) requirements. Essential guide for electricians, engineers, and electrical professionals.
Important Notice
This guide provides general NEC reference information. Always consult the current NEC code book and local electrical codes for your jurisdiction. Requirements may vary by location and application. For critical applications, consult a licensed professional electrician.
Voltage Drop Limits
NEC 210.19(A)(1) FPN No. 4
Maximum recommended voltage drop for branch circuits and feeders.
- Branch circuits: 3% maximum voltage drop
- Feeders: 5% maximum voltage drop
- Combined (branch + feeder): 5% maximum total
- These are recommendations, not mandatory requirements
📌 Note: Exceeding these limits reduces efficiency and can damage equipment
Wire Ampacity - Copper Conductors
NEC Table 310.16 (60°C)
Maximum current-carrying capacity for copper wire in typical conditions.
| 14 AWG | 15 Amperes |
| 12 AWG | 20 Amperes |
| 10 AWG | 30 Amperes |
| 8 AWG | 40 Amperes |
| 6 AWG | 55 Amperes |
| 4 AWG | 70 Amperes |
| 2 AWG | 95 Amperes |
| 1 AWG | 110 Amperes |
| 1/0 AWG | 125 Amperes |
| 2/0 AWG | 145 Amperes |
📌 Note: Values for 60°C insulation, 3 or fewer conductors in raceway/cable. Higher ratings for 75°C and 90°C insulation.
Circuit Breaker Sizing
NEC 210.20
Overcurrent protection requirements for branch circuits.
- Breaker rating must be ≥ 125% of continuous load
- Breaker rating must protect conductor ampacity
- Standard sizes: 15A, 20A, 25A, 30A, 35A, 40A, 45A, 50A, 60A, 70A, 80A, 90A, 100A
- Continuous load: operates for 3+ hours
- Use next higher standard size if calculated load falls between sizes
GFCI Protection Requirements
NEC Article 210.8
Ground Fault Circuit Interrupter protection for personnel safety.
- Bathrooms: All 125V, 15A and 20A receptacles
- Kitchens: Countertop receptacles
- Garages and unfinished basements
- Outdoors: All 125V, 15A and 20A receptacles
- Crawl spaces and below grade
- Laundry, utility, and wet bar sinks
- Within 6 feet of sinks, tubs, and showers
📌 Note: GFCI trips at 4-6 mA leakage current to prevent electric shock
AFCI Protection Requirements
NEC 210.12
Arc Fault Circuit Interrupter protection for fire prevention.
- All 120V, 15A and 20A branch circuits in dwelling units
- Bedrooms, living rooms, hallways, closets
- Dining rooms, family rooms, parlors, libraries
- Dens, sunrooms, recreation rooms
- Combination AFCI required at branch circuit origin
📌 Note: AFCI detects arc faults that can cause electrical fires
Minimum Circuit Requirements - Dwelling Units
NEC Article 210
Required branch circuits for residential installations.
- Small appliances (kitchen): Two 20A circuits minimum
- Laundry: One 20A circuit
- Bathroom: One 20A circuit (can serve multiple bathrooms)
- General lighting: Based on 3 VA per square foot
- Dedicated circuits for: dishwasher, disposal, microwave, refrigerator
- Central heating equipment: Dedicated circuit
Receptacle Spacing
NEC 210.52
Requirements for receptacle outlet placement in dwelling units.
- Wall receptacles: 12 feet maximum spacing
- No point along wall more than 6 feet from receptacle
- Kitchen countertops: 24 inches maximum spacing
- At least one receptacle in each bathroom
- At least one outdoor receptacle (front and back)
- At least one in garage, basement, and laundry area
Grounding Requirements
NEC Article 250
Equipment grounding and system grounding requirements.
- All metal equipment enclosures must be grounded
- Green or bare wire for equipment grounding
- Ground rod: 8 feet minimum depth
- Grounding electrode system required
- Ground wire sizing based on overcurrent protection
- No breaks in grounding path
📌 Note: Proper grounding is essential for safety and prevents electric shock
Box Fill Calculations
NEC 314.16
Maximum number of conductors allowed in electrical boxes.
- Each conductor: Counted by wire gauge volume
- Devices (switch/receptacle): 2 conductor equivalent
- Cable clamps: 1 conductor equivalent (one or more)
- Grounding wires: 1 conductor equivalent (total)
- Equipment grounding: 1 conductor equivalent
| 14 AWG | 2.00 cubic inches each |
| 12 AWG | 2.25 cubic inches each |
| 10 AWG | 2.50 cubic inches each |
| 8 AWG | 3.00 cubic inches each |
Working Clearances
NEC 110.26
Minimum working space around electrical equipment.
- Width: 30 inches minimum or width of equipment
- Depth (0-150V): 3 feet minimum
- Depth (151-600V): 3.5-4 feet depending on conditions
- Height: 6.5 feet minimum or height of equipment
- Clear and unobstructed workspace
- Adequate lighting and headroom
📌 Note: Ensures safe access for operation and maintenance
Service Entrance Requirements
NEC Article 230
Requirements for service conductors and equipment.
- Service disconnect: Maximum 6 disconnects
- Service disconnect location: Nearest entry point
- Clearly marked as service disconnect
- Minimum residential service: 100 Amperes
- Service grounding: Required at service equipment
- Weatherhead: 18 inches minimum above attachment
Flexible Cords and Cables
NEC Article 400
Permitted and prohibited uses of flexible cords.
- Permitted: Temporary wiring, portable equipment
- Permitted: Pendant fixtures, appliances
- Prohibited: Permanent wiring substitute
- Prohibited: Run through walls, ceilings, or floors
- Prohibited: Concealed behind walls
- Must be visible for entire length
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