Calculator Inputs
Example Data Table
| Case | Voltage | Load | Length | Material | Method | Suggested Size |
|---|---|---|---|---|---|---|
| Pump Feeder | 11 kV | 1200 kW | 350 m | Copper | Underground Duct | 120 mm² |
| Crusher Supply | 11 kV | 2400 kW | 600 m | Aluminum | Direct Buried | 300 mm² |
| Temporary Plant Board | 6.6 kV | 950 A | 220 m | Copper | Air Tray | 2 Runs x 240 mm² |
Formula Used
1. Current from power
Three phase: I = P / (√3 × V × pf)
Single phase: I = P / (V × pf)
2. Design current
Design Current = Base Current × Demand Factor × (1 + Growth Margin)
3. Required base ampacity per run
Required Ampacity = Design Current / (Parallel Runs × Ambient Factor × Grouping Factor × Additional Factor)
4. Voltage drop check
Three phase: Vd = √3 × I × (R cosφ + X sinφ) × L
Single phase: Vd = 2 × I × (R cosφ + X sinφ) × L
5. Short circuit check
Minimum Area = Isc × 1000 × √t / (k × Parallel Runs)
6. Embedded conductor resistance model
Copper R ≈ 22.5 / Area. Aluminum R ≈ 36 / Area. Area is in mm². R is in Ω/km.
7. k values used
Copper XLPE = 143. Aluminum XLPE = 94.
How to Use This Calculator
- Choose the system type and enter the operating voltage.
- Enter load current directly, or leave it blank and enter load power.
- Set power factor, route length, and conductor material.
- Select installation method and enter derating conditions.
- Enter short circuit current, fault clearing time, and parallel runs.
- Press calculate and review the recommended cable size.
- Use the CSV or PDF option to export the summary.
- Verify the final selection against the project standard and cable catalogue.
About Medium Voltage Cable Sizing
Medium voltage cable sizing affects safety, continuity, and project cost. A small cable can overheat during normal service. It can also suffer unacceptable voltage drop on long routes. A very large cable raises material, gland, and termination costs. Good sizing balances thermal duty, fault duty, voltage performance, and constructability. Designers should also review installation method, grouping, ambient conditions, and future growth. This calculator gives a practical starting point for planning work.
Why Construction Teams Use This Check
Construction projects often include feeders to pumps, chillers, cranes, package substations, and distribution boards. Route conditions change from one area to another. Some sections run in ducts. Others may be buried or fixed on trays. Ambient temperature may also rise in congested zones. Each condition changes cable performance. A quick check helps estimators, site engineers, and reviewers compare options before final vendor selection. It also improves discussions with the electrical consultant and procurement team.
What This Tool Evaluates
The calculator reviews three main limits. First, it checks current carrying capacity after applying correction factors. Second, it checks estimated voltage drop along the route. Third, it checks short circuit withstand using an adiabatic method. The governing cable size is the largest result from these checks. Parallel runs are also considered. This is useful when the project current is high and single run options become difficult to install.
Important Design Notes
Use the output as a design aid, not a final approval document. Manufacturer data, local rules, protection settings, conductor construction, sheath bonding, laying formation, and soil thermal resistivity can all change the result. Always compare the chosen size with the applicable standard, project specification, and selected cable catalogue. Final design should be signed off by a qualified engineer. Still, this tool can reduce early design time and improve consistency across repetitive construction estimates.
Practical Output for Site Work
The result panel shows the entered basis, derating impact, controlling sizes, and the final recommendation. This makes checking easier during tender reviews and method statement preparation. You can also export the summary for handover files or internal review notes. When route assumptions change, simply update the form and compare the revised recommendation immediately. That keeps revisions organized during busy build phases.
FAQs
1. Which result matters most?
The recommended size matters most. It is the largest size required by ampacity, voltage drop, and short circuit checks. Review the controlling check before procurement.
2. Can I use aluminum conductors here?
Yes. Select aluminum in the material field. The calculator changes resistance, k value, and embedded ampacity data for that choice.
3. Should I enter power or current?
Use current when it is already known from load schedules. Use power when current is not available. Entering current takes priority.
4. What if voltage drop controls the size?
Increase conductor area, shorten the route, improve power factor, or use parallel runs. Long feeders often become voltage drop limited.
5. Are parallel runs supported?
Yes. The calculator divides current and fault duty across equal parallel runs. Field installation and bonding arrangements still need engineering review.
6. Is this enough for final design approval?
No. Use it for planning and checking. Final approval should match the selected cable catalogue, protection study, and project specification.
7. What does the ambient factor do?
It adjusts the base ampacity for temperature. Higher ambient temperature reduces cable carrying capacity. Lower temperature may improve capacity.
8. Can I export the result summary?
Yes. Use the CSV button for spreadsheet records. Use the PDF button for a clean report that can be shared or archived.