Table ampacity
30 A12 AWG copper at the 90°C insulation column.
Wire Ampacity Calculator
Wire Ampacity Calculator
Check conductor ampacity after temperature, conductor-count, terminal, and load conditions. New here? Read the quick guide.
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Wire Ampacity Calculation
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Ampacity inputs and governing limits
- Project
- —
- Location
- —
- Prepared by
- —
- Selected conductor
- 12 AWG Copper · stranded
- Insulation rating
- 90°C (194°F)
- Terminal rating
- 75°C (167°F)
- Ambient temperature
- 30°C (86°F)
- Current-carrying conductors
- 3
- Continuous load
- 0 A
- Noncontinuous load
- 20 A
Calculated decision
- Base ampacity
- 30 A
- Ambient factor
- × 1.00
- Conductor-count factor
- × 1.00
- Corrected and adjusted
- 30 A
- Terminal limit
- 25 A
- Final planning limit
- 20 A
- Required load ampacity
- 20 A
- Minimum passing size
- 12 AWG
This calculator models a common Table 310.16 pathway only. Confirm the adopted edition, equipment markings, conductor listing, exceptions, and authority-having-jurisdiction requirements before installation.
Calculation inputs
Conductor selection
Load check
Continuous load is modeled at 125%; noncontinuous load is modeled at 100%.
Conductor sizing comparison
Minimum size under these entered conditions
Smallest supported size that passes12 AWG Copper
20 A planning limit versus 20 A required.
Currently selectedUse recommendation in Voltage Drop
| Conductor | Planning limit | Required | Result | Selection |
|---|---|---|---|---|
| 14 AWG | 15 A | 20 A | Revise | |
| 12 AWGMinimum passing | 20 A | 20 A | Pass | Selected |
Selected size details 12 AWG CopperPass
| ||||
| 10 AWG | 30 A | 20 A | Pass | |
| 8 AWG | 50 A | 20 A | Pass | |
| 6 AWG | 65 A | 20 A | Pass | |
Comparison uses the same material, insulation, terminal rating, ambient temperature, conductor count, and load entered above. It does not model parallel conductors or exceptions.
Transparent calculation
How the governing value was selected
Ambient correction
× 1.00Table factor for 30°C (86°F) ambient and 90°C (194°F) insulation.
Conductor adjustment
× 1.00100% for 3 current-carrying conductors.
Conditions-of-use result
30 A30 × 1.00 × 1.00.
Terminal limitation
25 AThe unadjusted 75°C table ampacity caps the conditions-of-use result.
Load requirement
20 A20 A + 125% × 0 A.
Small-conductor rule applied for this general planning check
NEC 240.4(D) generally limits this conductor to 20 A overcurrent protection. The calculator uses that lower value while excluding special permissions and exceptions.
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Method and scope
What this calculator does—and does not establish
This workflow begins with the 2023 NEC Table 310.16 ampacity for insulated conductors rated 0–2000 V, not more than three current-carrying conductors, and a 30°C ambient basis. It applies the selected ambient correction and conductor-count adjustment, then enforces the selected terminal-temperature column.
It does not determine whether a neutral counts, whether an adjustment exception applies, equipment listing compatibility, overcurrent-device selection beyond the displayed small-conductor planning cap, rooftop conditions, dwelling-service allowances, motor/HVAC rules, cable-tray ampacity, medium-voltage conductors, parallel installations, fault current, or complete code compliance.
Read the full methodologyPrimary references