Calculator Inputs
Example Data Table
| Case | Load | Voltage | Phase | Demand | Ambient | Required Ampacity | Example Conductor |
|---|---|---|---|---|---|---|---|
| Pump Feeder | 75 kW | 480 V | Three | 100% | 30°C | 125 A | 1 AWG Copper |
| HVAC Feeder | 120 kW | 480 V | Three | 90% | 40°C | 203 A | 3/0 AWG Copper |
| Process Line | 160 kW | 600 V | Three | 100% | 45°C | 248 A | 300 kcmil Aluminum |
Formula Used
Base Load Current
Three phase: I = (kW × 1000) / (V × √3 × PF)
Single phase: I = (kW × 1000) / (V × PF)
Demand Adjusted Current
Idemand = Ibase × Demand Factor
Continuous Load Adjustment
Idesign = Noncontinuous Current + (Continuous Current × 1.25)
Required Corrected Ampacity
Ampacity Required = Design Current / (Ambient Factor × Bundle Factor)
Estimated Voltage Drop
Vdrop = I × R × Length Factor
This page uses simplified resistance and ampacity tables for screening calculations.
How to Use This Calculator
- Enter total feeder load in kilowatts.
- Enter system voltage and power factor.
- Select single phase or three phase supply.
- Apply the expected demand factor.
- Enter the percent of load that is continuous.
- Enter ambient temperature and conductor count.
- Select conductor material and insulation rating.
- Add feeder length to estimate voltage drop.
- Press calculate and review the corrected ampacity.
- Use the suggested conductor as a design starting point.
Feeder Ampacity Design Guide
Feeder ampacity is the current a feeder conductor can carry safely. It depends on load, conductor material, insulation rating, ambient temperature, and conductor grouping. A good feeder ampacity calculator helps engineers screen a design quickly. It also helps users compare copper and aluminum options before final documentation.
This calculator starts with load current. It converts kilowatts into amperes by using system voltage, phase type, and power factor. Then it applies the demand factor. After that, it separates continuous and noncontinuous portions of the load. Continuous load is increased by 125 percent. That step reflects common feeder design practice for long running loads.
Derating is important in feeder sizing. Higher ambient temperature reduces allowable ampacity. More current carrying conductors in the same raceway also reduce usable capacity. This tool applies both adjustments. It then calculates the corrected ampacity required at the conductor rating. That gives a practical target for conductor selection.
The calculator also recommends a conductor size from a built in table. You can switch between copper and aluminum. You can also choose the insulation temperature rating. This helps you review realistic feeder options for engineering studies, budgeting, and early design checks. An estimated voltage drop is also shown when feeder length is entered. That helps you spot efficiency issues before installation.
Use this feeder ampacity calculator as a planning tool. Always compare results with the latest project documents, equipment ratings, and local code requirements. Final conductor sizing must consider termination limits, installation method, overcurrent protection, and site conditions. Short circuit duty and voltage drop limits may also affect the final design.
For best results, enter accurate load data. Use the expected operating power factor. Set a realistic demand factor. Enter the percentage of the load that is continuous. Choose the correct insulation class and conductor count. Then review the required ampacity, suggested size, and voltage drop together. A balanced review leads to safer feeder design and clearer engineering decisions.
Because feeder calculations are sensitive to assumptions, document every input. Save the result sheet for review. Recheck unusual ambient conditions, expansion plans, and future load growth. Small input changes can shift conductor size, cost, installation space, and material needs noticeably.
FAQs
1. What is feeder ampacity?
Feeder ampacity is the safe current carrying capacity of a feeder conductor after considering conductor type, insulation, ambient temperature, and installation conditions.
2. Why is continuous load increased by 125%?
Continuous loads can run for long periods. Applying 125% helps create a safer feeder design margin during extended operation.
3. Why does ambient temperature matter?
Higher ambient temperature raises conductor operating temperature. That reduces usable ampacity and may require a larger conductor size.
4. What does conductor bundling change?
More current carrying conductors in one raceway trap heat. That lowers effective ampacity and increases the corrected ampacity requirement.
5. Should I choose copper or aluminum?
Copper is compact and conductive. Aluminum is lighter and often less expensive. The best choice depends on space, budget, and terminations.
6. Is voltage drop included here?
Yes. The calculator gives an estimated voltage drop when feeder length is entered. It is intended for planning, not final field verification.
7. Can this replace a full code review?
No. Use it for engineering screening and quick comparisons. Final sizing must be checked against current code, equipment data, and project rules.
8. What if no conductor is recommended?
That means the required ampacity exceeds the simplified table range. You may need parallel conductors or a larger design review.