What ampacity means
Ampacity is the most current a wire can carry continuously without getting hotter than its insulation is rated for.
Where it matters on a electrical job
Ampacity sets the largest breaker you can put on a wire. It drops when wires are bundled, run hot or run in attics, which is why the same gauge is not always good for the same breaker. Size from the table, not from habit.
What the model code says
- The code defines ampacity as the maximum current a conductor can carry continuously under the conditions of use without exceeding its temperature rating. (IRC 2021, Chapter 35)
- For a one-family dwelling, ungrounded service conductors must be at least 100 amperes. (IRC 2021, Chapter 36)
Check which code edition your building department enforces for ampacity before you quote.
What it costs
Koira's electrical panel upgrade cost guide puts a typical job at $2,150, with most between $1,300 to $3,000. The guide shows its sources and what moves the price. The electrical load calculator prices a job line by line.
Work it out
- Free calculator: Electrical load calculator
- Cost guide: Electrical panel upgrade cost
- Licensing: Electrical license rules by state
- Tools, templates and guides: Free electrical resources
Sources: 2021 International Residential Code, Chapter 35, Electrical Definitions (ICC); 2021 International Residential Code, Chapter 36, Services (ICC). Checked October 9, 2026.