Calculator Inputs
Enter inverter and cable details below. The page checks current demand, derating, and voltage drop before recommending a practical conductor size.
Example Data Table
These sample cases show how voltage, length, and conductor material can change the recommended size significantly.
| Power | Voltage | Length | Material | Drop Limit | Approx. Suggested Size |
|---|---|---|---|---|---|
| 1200 W | 12 V | 2 m | Copper | 3% | 25 mm² |
| 2000 W | 24 V | 3 m | Copper | 3% | 25 mm² |
| 3000 W | 48 V | 5 m | Copper | 2% | 16 mm² |
| 1500 W | 24 V | 4 m | Aluminum | 3% | 35 mm² |
Formula Used
1) Base input current: I = P / (V × η)
Here, P is inverter power in watts, V is DC input voltage, and η is efficiency as a decimal.
2) Design current with derating: Idesign = I × Safety Factor / (Ctemp × Cgroup)
This adjusts current upward when ambient temperature rises or cables are grouped together.
3) Temperature-adjusted resistivity: ρT = ρ20 × [1 + α(T - 20)]
Resistivity increases with temperature, so long runs lose more voltage in warm conditions.
4) Required area by voltage drop: A = (ρT × 2L × I) / Vdrop
The factor 2L represents the full DC loop length. This is why short cable runs matter so much.
5) Estimated drop and power loss for a chosen size:
R = (ρT × 2L) / A
Vdrop = I × R
Ploss = I × Vdrop
These results are engineering estimates. Final conductor selection should still follow the applicable electrical code, insulation rating, termination limits, and manufacturer guidance.
How to Use This Calculator
- Enter the inverter's continuous output power in watts.
- Enter the DC supply voltage feeding the inverter.
- Set the expected inverter efficiency percentage.
- Measure the one-way cable length between source and inverter.
- Choose the maximum voltage drop you will allow.
- Select copper or aluminum conductor material.
- Add ambient temperature, grouping factor, and safety factor.
- Click the calculate button to view the recommended size above the form.
- Review the graph, summary table, and estimated drop details.
- Export the result as CSV or PDF when needed.
Frequently Asked Questions
1) Why does inverter cable size matter so much?
Inverter circuits often carry high DC current. Undersized wire increases voltage drop, heat, and wasted power. That can reduce inverter performance and stress batteries, terminals, and protective devices.
2) Why is one-way length doubled in the formula?
Current travels out and back through the circuit. DC voltage drop depends on total loop length, not just one conductor. That is why the calculator uses twice the entered cable distance.
3) Should I choose copper or aluminum?
Copper usually gives lower resistance and smaller sizes. Aluminum can reduce cost and weight, but it needs larger conductors and better termination practices. Follow connector and lug compatibility requirements carefully.
4) What voltage drop target is usually reasonable?
Many low-voltage DC designs aim for 2% to 3% drop. Sensitive systems may target even less. Shorter runs and larger cables help maintain inverter startup performance and battery efficiency.
5) What does the safety factor do?
The safety factor increases calculated current to provide margin for continuous operation, heating, and practical sizing. A common value is 1.25, though project rules or codes may require something different.
6) Why does temperature affect wire size?
Higher temperature raises conductor resistance and lowers usable ampacity. That means the same cable may run hotter and drop more voltage in warm areas, enclosed spaces, or tightly packed cable groups.
7) Is this result enough for final installation approval?
No. Use it as a sizing guide. Final installation should check code rules, insulation temperature rating, terminal limits, overcurrent protection, enclosure conditions, and manufacturer instructions for the inverter and battery system.
8) Why does low DC voltage need thicker wire?
Lower voltage systems draw more current for the same power. More current causes more loss and heating in the cable. That is why 12 V systems usually need much larger conductors than 48 V systems.