Inputs
Result
| Selection | Base Ampacity (A) | Ambient Factor | Bundling Factor | Corrected Ampacity (A) | Suggested Max OCPD (A) |
|---|---|---|---|---|---|
| Make a selection and click Calculate | |||||
How it works
This tool performs a lookup of base ampacity for the chosen size, material, and insulation temperature rating. Then it applies:
- Ambient temperature correction relative to 30°C base
- Bundling / number of current-carrying conductors derating
Values are conservative approximations for education and early planning. Always verify with the latest applicable standard and local codes.
Ambient correction factors (approx)
| Temp Range °C | 60°C | 75°C | 90°C |
|---|---|---|---|
| ≤30 | 1.00 | 1.00 | 1.00 |
| 31–35 | 0.94 | 0.94 | 0.96 |
| 36–40 | 0.88 | 0.88 | 0.91 |
| 41–45 | 0.82 | 0.82 | 0.87 |
| 46–50 | 0.75 | 0.75 | 0.82 |
| 51–55 | 0.67 | 0.67 | 0.76 |
| 56–60 | 0.58 | 0.58 | 0.71 |
| 61–70 | 0.41 | 0.41 | 0.58 |
| 71–80 | 0.26 | 0.26 | 0.41 |
Bundling derating by loaded conductors
| Loaded Conductors | Factor |
|---|---|
| 1–3 | 1.00 |
| 4–6 | 0.80 |
| 7–9 | 0.70 |
| 10–20 | 0.50 |
| 21–30 | 0.45 |
| 31–40 | 0.40 |
| 41+ | 0.35 |
Notes
- Small conductor rule advisory limits 14/12/10 AWG copper branch circuits to 15/20/30 A respectively
- OCPD suggestion rounds down to the nearest common standard size
- Use temperature rating appropriate to equipment terminations
FAQs
1) What is ampacity?
Ampacity is the maximum continuous current a conductor can carry without exceeding its temperature rating under specified installation conditions.
2) Why do ambient and bundling matter?
Higher ambient temperatures and groups of loaded conductors reduce heat dissipation. Derating keeps operating temperatures within insulation limits.
3) Which temperature rating should I pick?
Choose the insulation rating of the cable and consider equipment termination limits. Many terminations are limited to 60°C or 75°C.
4) Does voltage affect ampacity?
No directly. Ampacity is thermal. Voltage affects insulation selection and voltage drop but not thermal ampacity limits.
5) Can I use this for aluminum conductors?
Yes. Select aluminum and the calculator will use aluminum base ampacities with the same derating process.
6) How is OCPD chosen?
The tool rounds down to the nearest common protective device rating not exceeding corrected ampacity, subject to small conductor advisory where it applies.
7) Will this meet code?
This is an educational aid with conservative approximations. Always verify with the latest standard and local authority before making design decisions.
8) Does it check voltage drop?
No. Voltage drop depends on length and current. Use a dedicated voltage drop calculator alongside ampacity checks.