Quick Answer: Use this page to confirm the base Table 310.16 ampacity and the terminal temperature column before you calculate anything else. Then move to the Wire Size Calculator when you need the actual conductor size for a known load and run, or to the Ampacity Calculator when ambient temperature, conductor count, or terminal limits must be combined into one answer.
Based on NEC 2023 (NFPA 70), Table 310.16. Applies to 0–2000 V conductors in raceway, ≤3 current-carrying conductors, 30°C (86°F) ambient. Reviewed 2026-06-07.
Quick Answer: Wire Size by Amperage
What wire size do I need? Use NEC Table 310.16. For most residential work, apply the 60°C column (limited by terminal ratings):
| Wire Size | Copper 60°C | Copper 75°C | Aluminum 75°C | Common Use |
|---|---|---|---|---|
| 14 AWG | 15A | 20A | — | Lighting |
| 12 AWG | 20A | 25A | 20A | Receptacles |
| 10 AWG | 30A | 35A | 30A | Appliances |
| 8 AWG | 40A | 50A | 40A | Ranges, A/C |
| 6 AWG | 55A | 65A | 50A | Subpanels |
| 4 AWG | 70A | 85A | 65A | Service |
| 2 AWG | 95A | 115A | 90A | 100A service |
| 1/0 AWG | 125A | 150A | 120A | 125A service |
| 4/0 AWG | 195A | 230A | 180A | 200A service |
→ Use the Wire Size Calculator for final conductor selection, and the Ampacity Calculator when temperature or conductor-count adjustments control the answer.
NEC Table 310.16 - Complete Reference
Copper Conductors - Insulated Conductors (0-2000V)
Based on ambient temperature of 30°C (86°F), not more than 3 current-carrying conductors in raceway:
| AWG/kcmil | 60°C (TW, UF) | 75°C (THW, THWN) | 90°C (THHN, XHHW) |
|---|---|---|---|
| 18 | — | — | 14A |
| 16 | — | — | 18A |
| 14 | 15A | 20A | 25A |
| 12 | 20A | 25A | 30A |
| 10 | 30A | 35A | 40A |
| 8 | 40A | 50A | 55A |
| 6 | 55A | 65A | 75A |
| 4 | 70A | 85A | 95A |
| 3 | 85A | 100A | 115A |
| 2 | 95A | 115A | 130A |
| 1 | 110A | 130A | 145A |
| 1/0 | 125A | 150A | 170A |
| 2/0 | 145A | 175A | 195A |
| 3/0 | 165A | 200A | 225A |
| 4/0 | 195A | 230A | 260A |
| 250 kcmil | 215A | 255A | 290A |
| 300 kcmil | 240A | 285A | 320A |
| 350 kcmil | 260A | 310A | 350A |
| 400 kcmil | 280A | 335A | 380A |
| 500 kcmil | 320A | 380A | 430A |
Aluminum Conductors - Insulated Conductors (0-2000V)
| AWG/kcmil | 60°C (TW, UF) | 75°C (THW, THWN) | 90°C (THHN, XHHW) |
|---|---|---|---|
| 12 | 15A | 20A | 25A |
| 10 | 25A | 30A | 35A |
| 8 | 35A | 40A | 45A |
| 6 | 40A | 50A | 55A |
| 4 | 55A | 65A | 75A |
| 3 | 65A | 75A | 85A |
| 2 | 75A | 90A | 100A |
| 1 | 85A | 100A | 115A |
| 1/0 | 100A | 120A | 135A |
| 2/0 | 115A | 135A | 150A |
| 3/0 | 130A | 155A | 175A |
| 4/0 | 150A | 180A | 205A |
| 250 kcmil | 170A | 205A | 230A |
| 300 kcmil | 190A | 230A | 260A |
| 350 kcmil | 210A | 250A | 280A |
| 400 kcmil | 225A | 270A | 305A |
| 500 kcmil | 260A | 310A | 350A |
Understanding Temperature Ratings
Why Temperature Columns Matter
| Column | Insulation Types | When to Use |
|---|---|---|
| 60°C | TW, UF | Residential terminals (most common) |
| 75°C | THW, THWN, XHHW | Commercial, industrial |
| 90°C | THHN, XHHW-2 | Derating calculations only |
Critical Rule: Use the LOWER of conductor insulation rating OR terminal rating.
Most residential equipment has 60°C terminals → Use 60°C column even with 90°C wire.
Terminal Temperature Limitations
| Equipment | Typical Terminal Rating |
|---|---|
| Residential panels | 60°C or 75°C |
| Residential breakers | 60°C or 75°C |
| Commercial equipment | 75°C |
| Industrial equipment | 75°C or 90°C |
Wire Size for Specific Amperages
Quick Lookup: What Size Wire for... (Copper, 60°C)
| Amperage Needed | Minimum Wire Size | Notes |
|---|---|---|
| 15A | 14 AWG | Lighting circuits |
| 20A | 12 AWG | Receptacles |
| 30A | 10 AWG | Dryers, small A/C |
| 40A | 8 AWG | Ranges, large A/C |
| 50A | 6 AWG | Ranges, EV chargers |
| 60A | 4 AWG (55A) or 6 AWG 75°C | Subpanels |
| 70A | 4 AWG | Service |
| 100A | 2 AWG (95A) or 1 AWG | 100A service |
| 125A | 1/0 AWG | 125A service |
| 150A | 2/0 AWG (145A) or 3/0 AWG | 150A service |
| 200A | 4/0 AWG (195A) or 250 kcmil | 200A service |
Quick Lookup: Aluminum Wire Sizes (75°C)
| Amperage | Aluminum Size | Copper Equivalent |
|---|---|---|
| 100A | 1/0 AWG | 2 AWG |
| 125A | 2/0 AWG (135A) | 1/0 AWG |
| 150A | 3/0 AWG (155A) | 2/0 AWG |
| 200A | 4/0 AWG (180A) | 4/0 AWG |
Residential Service Entrance Sizing
NEC 310.12 Service Conductor Sizing
| Service Size | Copper (60°C) | Copper (75°C) | Aluminum (75°C) |
|---|---|---|---|
| 100A | 2 AWG | 3 AWG | 1/0 AWG |
| 125A | 1/0 AWG | 1 AWG | 2/0 AWG |
| 150A | 3/0 AWG | 2/0 AWG | 3/0 AWG |
| 200A | 4/0 AWG | 4/0 AWG | 4/0 AWG |
| 225A | 250 kcmil | 250 kcmil | 250 kcmil |
| 400A | — | 500 kcmil | 500 kcmil |
Note: Service conductors may use 83% rule per NEC 310.12 for dwelling units.
Parallel Conductors
NEC 310.10(G) Parallel Conductor Requirements
When running conductors in parallel (1/0 AWG or larger):
| Requirement | Specification |
|---|---|
| Minimum size | 1/0 AWG |
| Same length | Required |
| Same material | Required (all copper or all aluminum) |
| Same circular mil area | Required |
| Same insulation type | Required |
| Same termination method | Required |
Parallel Ampacity Calculation:
Total Ampacity = Single Conductor Ampacity × Number of Conductors
Example: Two 4/0 AWG copper THHN in parallel:
Total = 260A × 2 = 520A
Common Insulation Types
Insulation Type Reference
| Type | Temperature | Description | Common Use |
|---|---|---|---|
| TW | 60°C | Thermoplastic, wet | General purpose, wet locations |
| THW | 75°C | Thermoplastic, heat-resistant, wet | General purpose |
| THWN | 75°C | THW with nylon jacket | Conduit, raceways |
| THHN | 90°C | Thermoplastic, high-heat, nylon | Dry locations |
| XHHW | 75°C wet, 90°C dry | Cross-linked polyethylene | Wet/dry locations |
| XHHW-2 | 90°C wet/dry | Enhanced XHHW | Industrial |
| USE | 75°C | Underground service entrance | Direct burial |
| UF | 60°C | Underground feeder | Direct burial |
Worked Examples
Example 1: Residential 20A Circuit
Given: Kitchen receptacle circuit, 20A
Solution:
- Load: 20A
- Look up Table 310.16, 60°C column (residential terminals)
- Find: 12 AWG = 20A ✓
Answer: Use 12 AWG copper (minimum)
Example 2: 100A Subpanel
Given: Install 100A subpanel in detached garage
Solution:
- Load: 100A
- Table 310.16, 60°C: 2 AWG = 95A (too low)
- Table 310.16, 75°C: 3 AWG = 100A ✓
- Check terminal rating: If 75°C rated → 3 AWG OK
- If 60°C terminals → Use 1 AWG (110A)
Answer: Use 3 AWG copper (75°C terminals) or 1 AWG copper (60°C terminals)
Example 3: 200A Service with Aluminum
Given: 200A residential service, aluminum conductors
Solution:
- Load: 200A
- Table 310.16, Aluminum 75°C: 4/0 = 180A (close)
- Per NEC 310.12, dwelling services can use 83% rule
- 200A × 0.83 = 166A required
- 4/0 aluminum = 180A > 166A ✓
Answer: Use 4/0 AWG aluminum for 200A dwelling service
Example 4: Wire in Hot Attic
Given: 12 AWG THHN in 50°C (122°F) attic
Solution:
- Base ampacity (90°C): 30A
- Temperature correction factor (46-50°C): 0.82
- Corrected: 30A × 0.82 = 24.6A
- Terminal limitation (60°C): 20A maximum for 12 AWG
Answer: Maximum load is 20A (limited by terminal, not corrected ampacity)
Copper vs Aluminum Comparison
When to Use Each Material
| Factor | Copper | Aluminum |
|---|---|---|
| Ampacity | Higher per size | ~78% of copper |
| Cost | Higher | Lower (larger size offsets) |
| Weight | Heavier | Lighter |
| Size for same ampacity | Smaller | 1-2 sizes larger |
| Terminations | Standard | Requires AL-rated devices |
| Common use | Branch circuits | Service entrance, feeders |
Copper to Aluminum Equivalents
| Copper Size | Copper 75°C | Aluminum Equivalent | Aluminum 75°C |
|---|---|---|---|
| 4 AWG | 85A | 2 AWG | 90A |
| 2 AWG | 115A | 1/0 AWG | 120A |
| 1/0 AWG | 150A | 3/0 AWG | 155A |
| 4/0 AWG | 230A | 250 kcmil | 205A |
Common Mistakes to Avoid
| Mistake | Why It's Wrong | Correct Approach |
|---|---|---|
| Using 90°C ampacity at 60°C terminals | Exceeds terminal rating | Use terminal rating column |
| Ignoring aluminum requirements | Improper termination | Use AL-rated devices, anti-oxidant |
| Not checking terminal temperature | May overload connections | Verify breaker/equipment rating |
| Mixing copper and aluminum | Galvanic corrosion | Use proper bimetallic connectors |
Related Calculators
| Calculator | Use When... |
|---|---|
| Wire Size Calculator | Selecting conductor for load |
| Voltage Drop Calculator | Long distance runs |
| Conduit Fill Calculator | Determining conduit size |
| Breaker Sizing Calculator | Matching wire to protection |
Summary
Key Rules:
- Use 60°C column for most residential (terminal limitation)
- 14 AWG → 15A, 12 AWG → 20A, 10 AWG → 30A (fixed per NEC)
- Aluminum is ~78% of copper ampacity (use 1-2 sizes larger)
- Check terminal rating - limits usable ampacity
- Service conductors may use 83% rule (NEC 310.12)
FAQ
What is wire ampacity?
Ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. It's determined by conductor size, insulation type, installation conditions, and ambient temperature.
Why are there different temperature columns?
Different insulation types have different maximum operating temperatures. You must use the ampacity for the weakest point in the circuit - usually the terminal/connection temperature rating, not the wire's insulation rating.
Can I use aluminum wire for branch circuits?
Aluminum is generally not recommended for 15A and 20A branch circuits due to historical connection issues. It's commonly used for service entrance conductors and large feeders when properly terminated.
What size wire for 200 amp service?
For 200A residential service: 4/0 AWG copper (195A, uses 83% rule) or 4/0 AWG aluminum at 75°C. Verify local code requirements as some jurisdictions require larger sizing.
How do I account for ambient temperature?
Apply NEC Table 310.15(B)(1) correction factors to the base ampacity. Higher ambient temperatures reduce ampacity. Example: 90°C wire at 40°C ambient uses 0.91 factor.
What size wire for 30 amps?
Use 10 AWG copper (30A at 60°C per NEC Table 310.16). Typical 30A loads include electric dryers, water heaters, and small air conditioners. Always verify your equipment's terminal temperature rating before selecting the ampacity column.
What size wire for 50 amps?
Use 6 AWG copper at 60°C (55A, suitable for a 50A breaker) or 8 AWG copper at 75°C (exactly 50A). Typical 50A loads include electric ranges and Level 2 EV chargers. Confirm terminal ratings before applying the 75°C ampacity column.