Cable Sizing Calculator per NEC (NFPA 70) for Residential Installations
Conductor sizing for NEC 2026 residential installations uses Table 310.16 ampacity values for 60 °C or 75 °C conductor terminations, applies Article 310.15(C) adjustment factors for more than three current-carrying conductors, calculates dwelling load per Article 220 Parts III and IV, and recommends a maximum 3% voltage drop per Section 210.19(A) Informational Note No. 4.
Quick Reference Table
| NEC 2026 Residential Conductor Sizing References — NEC (NFPA 70) (2026 Edition) | ||
|---|---|---|
| Parameter | Value / Requirement | Clause Reference |
| Ampacity table | Allowable ampacities for insulated conductors | Table 310.16 |
| Adjustment factors | Derating for more than 3 current-carrying conductors | Article 310.15(C)(1) |
| Temperature correction | Ampacity correction for ambient above 30 °C | Table 310.15(B)(1) |
| Dwelling load calculation | Standard and optional methods for dwellings | Article 220, Parts III-IV |
| Voltage drop recommendation | 3% branch circuit, 5% total feeder + branch | Section 210.19(A) Informational Note No. 4 |
How to Calculate Cable Sizing for Residential Installations
- 1
Calculate the dwelling unit load
Use Article 220 Part III (standard method) or Part IV (optional method) to calculate the total dwelling load including general lighting (3 VA/ft²), small appliance circuits (1500 VA each), and fixed appliances.
- 2
Determine branch circuit design current
Identify the load on each branch circuit — 15 A or 20 A general purpose, 20 A kitchen/laundry, dedicated circuits for HVAC, water heater, and dryer per Article 210.
- 3
Select conductor from Table 310.16
Choose the conductor size with ampacity meeting or exceeding the overcurrent device rating. For residential, terminations are typically rated 60 °C per Section 110.14(C)(1) for circuits under 100 A.
- 4
Apply adjustment and correction factors
Derate for conduit fill exceeding 3 conductors per Article 310.15(C)(1) and apply temperature correction from Table 310.15(B)(1) for ambient temperatures above 30 °C (attics, crawl spaces).
- 5
Check voltage drop
Calculate voltage drop and verify it does not exceed the 3% branch circuit recommendation of Section 210.19(A) Informational Note. For the total feeder plus branch circuit, the target is 5%.
Try the Cable Sizing Calculator
Run compliant NEC (NFPA 70) calculations for residential installations — free, instant results with full clause references.
Calculate Cable Sizing NowNEC vs IEC 60364 Cable Sizing Comparison
| Parameter | NEC | IEC 60364 |
|---|---|---|
| Conductor sizing unit | AWG/kcmil | mm² |
| Voltage drop recommendation | 3% branch / 5% total | 4% lighting / 5% other |
| Reference ambient temp | 30°C | 30°C (air), 20°C (ground) |
| Continuous load multiplier | 1.25x required | Not explicitly required |
| Ampacity table | Table 310.16 (60/75/90°C) | Tables B.52.2–B.52.13 |
| Conduit fill limit | 40% for 3+ conductors | Not specified (derating instead) |