Calculator
Example data table
| Example | Phase | Power | Voltage | Power factor | AC current | DC current | Design current |
|---|---|---|---|---|---|---|---|
| Small rooftop inverter | Single phase | 5 kW | 240 V | 0.98 | 21.259 A | 8.547 A at 600 V | 33.217 A |
| Commercial inverter | Three phase | 10 kW | 400 V | 0.98 | 14.731 A | 17.094 A at 600 V | 23.017 A |
| Larger plant section | Three phase | 25 kW | 480 V | 0.99 | 30.380 A | 42.735 A at 600 V | 47.469 A |
Formula used
Single phase AC current: I = P / (V × PF)
Three phase AC current: I = P / (√3 × VLL × PF)
Apparent power: S = PkW / PF
DC input power: Pdc = Pac / efficiency
DC input current: Idc = Pdc / Vdc
Design current: Idesign = Iac × continuous factor × safety factor
Required conductor ampacity: Ampacity = Idesign / derating factor
Single phase voltage drop: VD = 2 × I × R × L
Three phase voltage drop: VD = √3 × I × R × L
How to use this calculator
Enter the inverter label or project name first. Choose single phase or three phase output. Add rated AC power, voltage, power factor, efficiency, and DC voltage. Then enter string current values when you want a DC short circuit review. Add cable length and conductor resistance for voltage drop checking. Press Calculate to show results above the form. Use the CSV or PDF buttons to export the same calculation.
About SMA inverter current calculations
Why inverter current matters
SMA inverter current calculations help designers compare nameplate power with real operating current. A solar inverter may look simple on its label, yet current changes with voltage, phase type, efficiency, and power factor. These values affect breakers, disconnects, conductors, and voltage drop. An estimate also helps spot undersized equipment before work starts.
AC output planning
The AC side carries usable power to a panel, load center, or grid connection. Single phase current uses power divided by voltage and power factor. Three phase current uses the square root of three because the load is shared between phases. Lower power factor increases current. That means the same kilowatt rating may need larger protection when power factor is reduced.
DC input planning
The DC side receives energy from solar strings or a battery source. Input current is normally higher than a perfect conversion would suggest because every inverter has losses. The calculator estimates DC input power by dividing AC output power by efficiency. It then divides that value by DC voltage. Lower DC voltage raises current and may increase cable loss.
Protection and derating
Continuous inverter output often needs extra margin. Many designs apply a continuous load factor, then add a planning safety factor. The adjusted value helps choose a breaker or disconnect above the calculated load. Conductors also need margin for heat, conduit fill, rooftop exposure, and local rules. The derating field lets you convert design current into required conductor ampacity.
Voltage drop review
Long cable runs waste power. The calculator estimates voltage drop from current, one way distance, and conductor resistance. For single phase circuits it uses the round trip path. For three phase circuits it uses the line current relation. The result shows percent drop against your target. A high result suggests shorter runs, larger conductors, or a layout change.
Good engineering practice
Use this calculator for early sizing, comparison, and documentation. Then verify all settings with the inverter manual, site voltage, utility limits, and electrical code. Real projects may need surge ratings, temperature ratings, grounding checks, rapid shutdown equipment, and certified drawings. Treat the result as a planning aid, not a final approval. Record assumptions, export the report, and keep it with the project file.
FAQs
1. What current does this calculator estimate?
It estimates AC output current, DC input current, adjusted design current, breaker size, conductor ampacity, and voltage drop. It is intended for early electrical planning.
2. Can it be used for single phase inverters?
Yes. Select single phase and enter the correct line voltage. The calculator then uses the single phase current formula.
3. Can it be used for three phase inverters?
Yes. Select three phase and enter line to line voltage. The calculator applies the square root of three formula.
4. Why does power factor affect current?
Lower power factor means more apparent power is needed for the same real power. That raises current and may change protective device sizing.
5. Why is DC current different from AC current?
DC current depends on DC voltage and inverter losses. Efficiency reduces usable conversion, so input power must be higher than AC output power.
6. What breaker value should I use?
The shown breaker is only the next standard estimate above design current. Confirm final selection with manuals, terminals, conductor ratings, and local rules.
7. What is conductor derating?
Derating accounts for heat and installation limits. A lower derating percentage increases the required conductor ampacity shown by the calculator.
8. Is this a final engineering design?
No. Use it as a planning guide. Final designs should be checked by qualified professionals using approved inverter documents and electrical codes.