Inverters & equipment

AC cable loss calculator

Enter your inverter's AC output, voltage, wire run, and power factor. Get the power lost in watts, as a percent of output, and projected as annual kWh and dollars.

Your numbers

1 Project details Optional
Shown on your exported report. Leave blank to skip.
2 Inverter AC output
Rated continuous AC output from the inverter nameplate.
240V single-phase is standard for most US residential systems.
Most residential inverters run near 1.0 (unity). Check the datasheet if unsure.
3 Wire run
Measure one-way along the actual routed path from inverter to panel.
Use the gauge from the wire gauge sizing calculator.
4 Production estimate
Peak sun hours for your location; 4-6 is typical across most of the US.
Your utility's retail rate, used to translate lost energy into a dollar figure.

How it works

Three steps to your AC cable loss

Step 1

Get the inverter's AC nameplate data

Pull continuous AC output, voltage, and phase straight from the inverter's nameplate or datasheet; the grid tie inverter sizing calculator can help if you're still finalizing your inverter choice. The wiring loss output calculator shows how this number plays out in real production.

Step 2

Confirm the wire gauge for this run

Use the gauge you landed on from the wire gauge sizing calculator for the inverter-to-panel segment specifically, since it's usually a different gauge than the DC home run. The connector and wiring inspection cost estimator is worth running once this number is in hand.

Step 3

Compare against the DC leg

Run the DC cable loss calculator for the array-to-inverter run too, so you see the full picture of where resistive losses are adding up across the whole system.

Understanding AC cable loss

Why the inverter-to-panel run gets its own check

The AC segment from inverter to main panel, or panel to the utility interconnection point, is a separate circuit from the DC home run, with its own current, voltage, and typically a shorter distance. The DC cable loss calculator covers the array side; this tool covers the inverter's output side, and the two are rarely identical since AC circuits usually run at a higher voltage and lower current for a given power delivered.

Why power factor changes the current, even at the same kW

An inverter's kW rating is real power, but the actual current flowing through the wire depends on both voltage and power factor. Most residential grid-tie inverters run close to unity power factor (1.0), so this rarely matters much in practice, but some inverters and interconnection agreements call for a lower power factor to help support grid voltage, and that lower power factor means more current for the same real power output, which increases resistive loss in the wire.

Why three-phase changes the math

Larger commercial and some larger residential systems tie into three-phase service, where the same real power splits across three conductors instead of two. This calculator applies the standard square root of 3 factor to both the current calculation and the resistance figure for three-phase circuits, which generally results in lower loss than an equivalent single-phase circuit carrying the same power over the same distance and gauge.

Why AC loss is often the smaller of the two legs

In a typical residential system, the AC run from inverter to panel is short, often under 50 feet, while the DC home run from a rooftop array can be well over 100 feet. Combined with AC circuits commonly running at a higher voltage than DC strings, which means less current for the same power, the AC leg often comes out with a smaller loss percentage than the DC leg. That's not guaranteed though, especially on detached structures or ground-mount systems with a long AC run back to the main panel, so it's worth checking both rather than assuming, and the wiring loss output calculator shows how this same resistive loss shows up on the production side rather than as a wire-sizing exercise. For a broader view of how these losses fit into overall system output, NREL's PVWatts calculator models inverter and array performance in detail, including the downstream effect of wiring losses like these.

What this tool doesn't cover

This calculator estimates resistive wire loss only, using the standard 75C resistivity constants for copper and aluminum given in NEC Table 310.16. It doesn't account for transformer losses or inverter conversion efficiency, which are separate mechanisms elsewhere in the system, and it also leaves out connector resistance, which the connector and wiring inspection cost estimator covers separately since loose or corroded connections add resistance this tool doesn't model. For the full DC-side picture, pair this with the DC cable loss calculator and confirm final wire selection against the voltage drop calculator and a licensed electrician.

Questions

Frequently asked

A 7.6kW inverter at 240V single-phase over a 50 foot run on 8 AWG copper loses roughly 78W, about 1% of output. Find the AC current from the inverter's kW output, voltage, and power factor, then apply that current to the wire's round-trip resistance to get power loss in watts.

For the same real power output in kW, a lower power factor means more current has to flow to deliver that power, and resistive loss scales with current squared. Most residential solar inverters run close to unity power factor, but commercial inverters or systems with reactive loads can run lower, which increases wire losses for the same kW delivered.

Often, yes, mainly because the AC run from inverter to panel is typically much shorter than the DC home run from a rooftop array, and AC circuits commonly operate at a higher voltage, which means less current for the same power and therefore less resistive loss. Every system is different, so it's worth checking both legs rather than assuming.

Three-phase circuits typically carry less current per conductor than single-phase for the same power delivered, since the load splits across three phases instead of two conductors. This calculator applies the standard sqrt(3) factor for three-phase current and resistance so the loss estimate reflects that difference.

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