Analyze medium-voltage cable ampacity using practical derating inputs. Review thermal limits, parallel runs, and margins. Build reliable cable selections for demanding field conditions today.
Corrected ampacity per run = Base ampacity × insulation factor × temperature factor × installation factor × grouping factor × soil factor × burial depth factor × harmonic factor.
Total corrected ampacity = Corrected ampacity per run × number of parallel runs.
Loading percent = Design current ÷ total corrected ampacity × 100.
Three-phase voltage drop = √3 × I × (R × cosφ + X × sinφ) × route length.
This calculator uses practical reference values for pre-design work. It is not a substitute for detailed manufacturer data or full standard-based thermal modeling.
| Case | Material | Insulation | Size | Method | Design Current | Parallel Runs | Estimated Result |
|---|---|---|---|---|---|---|---|
| Plant feeder | Copper | XLPE | 240 mm² | In air on tray | 250 A | 1 | Pass with healthy thermal margin |
| Buried export run | Aluminum | XLPE | 400 mm² | Buried duct bank | 420 A | 2 | Pass after soil and grouping corrections |
| Heavy drive load | Copper | EPR | 185 mm² | In air inside conduit | 300 A | 1 | Check harmonics and voltage drop closely |
MV cable ampacity defines the current a cable can carry without exceeding its thermal limit. This matters in substations, plants, solar farms, and utility feeders. A cable that runs too hot ages faster. Its insulation can degrade early. Good sizing protects reliability and service life.
The nameplate conductor size is only the starting point. Real installation conditions change the result. Air temperature affects heat rejection. Soil temperature and soil resistivity affect buried cables. Grouped circuits reduce cooling. Conduit and duct banks trap heat. Harmonics can also raise losses. Parallel runs may improve capacity when the installation is balanced.
Derating factors turn a reference ampacity into a project ampacity. This makes the selection more realistic. A cable in free air performs differently from the same cable in a buried duct bank. A deep trench behaves differently from a shallow burial. That is why correction factors are useful during front-end design and bid work.
This calculator combines a base ampacity table with practical correction factors. It returns corrected ampacity per run and total ampacity for parallel sets. It also shows loading percent, thermal margin, and an estimated voltage drop. That extra voltage view helps engineers avoid choosing a cable that passes thermally but performs poorly electrically.
A pass means the corrected ampacity exceeds the design current. Margin shows how much room is left. Lower loading usually improves operating comfort. High voltage drop may still require a larger size. Use the recommended size as a screening value, then confirm with project documents, manufacturer data, and the governing standard before procurement.
It is the allowable continuous current for a medium-voltage cable under stated installation conditions. The value depends on conductor size, insulation, ambient or soil temperature, grouping, and how well the cable can release heat.
Grouped circuits heat each other. That extra thermal buildup reduces cooling. Because of that, each circuit usually carries less current than it would in a single isolated installation.
Higher soil resistivity means poorer heat transfer. Buried cables then run hotter for the same load. The usable ampacity falls unless the design adds more conductor area, spacing, or parallel runs.
A larger cable usually lowers resistance and helps voltage drop. Still, route length, load current, power factor, and parallel arrangement also matter. Thermal pass alone does not guarantee acceptable voltage performance.
Use parallel runs when one conductor cannot safely carry the design load or when voltage drop must be improved. Parallel sets can also help installation practicality on long, heavy MV routes.
Yes. Harmonics can increase conductor and metallic screen losses. That extra loss raises temperature. A harmonic derating check is helpful when large drives, converters, or non-linear industrial loads are present.
This tool is best for pre-design and screening. Final procurement should use detailed manufacturer ratings, project-specific installation data, and the exact code or standard required by the job.
Copper usually carries more current for the same size and has lower resistance. Aluminum is lighter and often cheaper. The better option depends on cost, weight, terminations, space, and voltage drop limits.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.