Complete Guide to Wire Sizing
The Wire Size Calculator selects AWG/kcmil based on NEC ampacity, voltage drop, material, and installation. Covers 60–90°C, copper/aluminum, conduit/free air. Our free tool ensures code-compliant, safe wiring.
What is Wire Sizing?
AWG = function of current, drop, length. NEC 310.15: ampacity tables. Our Wire Size Calculator uses Table 310.16 + drop formula.
Why Proper Sizing?
Prevents:
- Overheating: Fire risk.
- Voltage Drop: Equipment failure.
- Code Violation: Inspection fail.
- Inefficiency: Energy loss.
Use with Voltage Drop and Breaker Size.
How to Size Wire
Steps:
- Load: 125% continuous.
- Ampacity: Table 310.16.
- Drop: VD = 2×I×L×ρ/CM (single).
- Largest: Meets both.
Example: 50A, 150 ft, 240V = #6 Cu.
NEC Ampacity Table (75°C Copper, Conduit)
| AWG/kcmil | Amps | AWG/kcmil | Amps |
|---|---|---|---|
| 14 | 20 | 3 | 115 |
| 12 | 25 | 2 | 130 |
| 10 | 35 | 1 | 150 |
| 8 | 50 | 1/0 | 170 |
| 6 | 65 | 2/0 | 195 |
| 4 | 85 | 3/0 | 225 |
Aluminum vs Copper
| Load (A) | Copper | Aluminum |
|---|---|---|
| 50 | #8 | #6 |
| 100 | #3 | #1 |
| 200 | 3/0 | 250 kcmil |
Key Factors
- Continuous: ×1.25.
- Ambient: Derate >30°C.
- Conduit Fill: >3 conductors.
- Length: Drop dominant >100 ft.
Practical Applications
For:
- Subpanel: 100A feeder.
- EV Charger: 48A, 50 ft.
- Motors: FLA × 1.25.
- Lighting: Branch circuits.
Tips
- Upsize: Future-proof.
- 90°C: THHN in conduit.
- Aluminum: Terminate properly.
- Check Drop: Even if ampacity met.
Common Mistakes
- No 125%: Continuous loads.
- Ignore Drop: Long runs.
- Wrong Table: 60°C vs 75°C.
- Parallel: <1/0 not allowed.
Advanced
- Derating: NEC 310.15(B).
- VD Formula: Includes reactance.
- Conduit Fill: Chapter 9.
- Ground Size: Table 250.122.
Conclusion
Correct wire sizing ensures safety and efficiency. Our Wire Size Calculator automates NEC compliance. Pair with Construction tools for complete projects. Wire smart with 1000 Calculators.