Ampacity Derating
Calculator
Results
- Derated ampacity (A)
- 22.528
- Spare capacity (A)
- 2.528
- Utilisation (%)
- 88.778409
Electrical results
| Derated ampacity (A) | 22.528 |
| Spare capacity (A) | 2.528 |
| Utilisation (%) | 88.778409 |
formula-map diagram
- Derated ampacity (A)
- 22.528
- Spare capacity (A)
- 2.528
- Utilisation (%)
- 88.778409
Electrical relationship
Formula
I_allowed = I_base × k_temperature × k_grouping= 22.528
Note
This is a simplified model: it applies the textbook relationship to the numbers you entered and assumes ideal components, steady-state sinusoidal conditions, balanced loads and copper resistivity of 0.0172 Ω·mm²/m at 20 °C. It ignores component tolerances, temperature drift, skin effect, harmonics, inrush, transformer and battery losses, and it is not a substitute for the wiring code that applies where you are. Have any installation sized and verified by a licensed electrician or engineer.
More in Electrical engineering
See all →Frequently asked questions
What does ampacity derating mean?+
Ampacity is the maximum current a conductor can carry continuously without overheating; derating reduces that rated value to account for real-world conditions like higher ambient temperature or multiple current-carrying conductors bundled together.
Why does bundling multiple wires together reduce their ampacity?+
Each current-carrying conductor generates heat, and when several are bundled in the same conduit or cable, they can't dissipate that heat as effectively since they're insulating each other, so codes require reducing the allowed current per conductor as the count increases.
How does ambient temperature affect ampacity?+
Conductor ampacity ratings are based on a reference ambient temperature (commonly 30°C or 86°F); if the actual installation environment is hotter, the wire has less thermal headroom before reaching its insulation's temperature limit, so the allowed current must be reduced using a temperature correction factor.
What happens if I ignore derating and overload a cable?+
The conductor can run hotter than its insulation is rated for, accelerating insulation breakdown and creating a fire hazard over time — even if it doesn't fail immediately, the effective lifespan of the wiring is shortened.
Are derating factors the same for every type of insulation?+
No, different insulation types (like THHN vs. THW) have different maximum temperature ratings, which changes both their base ampacity and how much correction is needed for a given ambient temperature — always use the derating table that matches your specific conductor insulation type.