Commercial & small business
Most commercial buildings run on three-phase power. See the line current your system will draw before your electrician sizes conductors and breakers.
How it works
Step 1
Use the AC size, not the array's DC size. The commercial inverter sizing calculator can help if you haven't settled on an inverter yet.
Step 2
Check your electrical panel or utility documentation, since assuming the wrong voltage significantly changes the current calculation. The interconnection cost estimator is also based on your final AC rating, so this step feeds directly into that one.
Step 3
Code-required margins and derating factors apply on top of this base calculation. The permitting cost estimator covers what getting the final design approved typically costs.
A 150 kW system at 480V line-to-line and a 0.99 power factor, typical for a commercial inverter, produces a line current of about 182.2 amps. The formula divides system power by the square root of 3 times line voltage times power factor, which is the standard three-phase power calculation. Feed this figure into the interconnection cost estimator once your electrician has confirmed final conductor and breaker sizing. Before you lock in a number, compare it with solar inverter size calculator. A size estimate is only half the decision for a business. The quick financing comparison tool in our Financing section can help you work out which way to pay for the system costs less.
Three-phase power delivers energy more efficiently and with less conductor material than single-phase for the same power level, which matters at commercial scale. Most commercial buildings already have three-phase electrical service, so a three-phase inverter matches the building's existing infrastructure rather than requiring a conversion, similar to how the permitting cost estimator assumes standard commercial electrical service in its baseline figures. IEEE 1547-2018 covers this point in more depth.
Higher line voltage delivers the same amount of power at lower current, since power equals voltage times current. Common commercial voltages like 208V, 480V, and 600V each produce meaningfully different current for the same system size, which is why confirming your site's actual service voltage matters before sizing conductors and breakers, a step worth confirming alongside the solar warranty value calculator when reviewing equipment specs, and the inverter oversizing calculator if you're weighing a higher DC-to-AC ratio for the same electrical service.
It's the starting point, but actual conductor and breaker sizing also accounts for code-required safety margins, ambient temperature derating, and continuous-duty factors specific to solar circuits. NEC Article 690 applies a combined 125% continuous-duty and irradiance safety margin on top of this base current calculation, which is why final wire gauge always comes out larger than the raw line current figure alone would suggest, a detail worth reviewing in the National Electrical Code itself. A licensed electrician needs to apply those additional factors to the calculated current before finalizing equipment selection, and the commercial inverter sizing calculator is a useful companion for confirming the AC rating that feeds into this calculation. The inverter itself is also certified against IEEE 1547-2018, the performance standard governing how it responds to voltage and frequency abnormalities on a three-phase grid connection, and the solar inverter size calculator in our inverters and equipment section walks through the same DC-to-AC ratio logic at a smaller scale.
Questions A commercial roof has its own costs and limits. The roof inspection cost before solar estimator in our Solar + Roofing Integration section can help you check whether your roof is ready before you commit to a size.
A 150 kW system at 480V line-to-line and a 0.99 power factor, typical for a commercial inverter, produces a line current of about 182.2 amps. The formula divides system power by the square root of 3 times line voltage times power factor, which is the standard three-phase power calculation.
Three-phase power delivers energy more efficiently and with less conductor material than single-phase for the same power level, which matters at commercial scale. Most commercial buildings already have three-phase electrical service, so a three-phase inverter matches the building's existing infrastructure rather than requiring a conversion.
Higher line voltage delivers the same amount of power at lower current, since power equals voltage times current. Common commercial voltages like 208V, 480V, and 600V each produce meaningfully different current for the same system size, which is why confirming your site's actual service voltage matters before sizing conductors and breakers.
It's the starting point, but actual conductor and breaker sizing also accounts for code-required safety margins, ambient temperature derating, and continuous-duty factors specific to solar circuits. A licensed electrician needs to apply those additional factors to the calculated current before finalizing equipment selection.
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