The circuit breaker size for solar panels depends on which circuit you are protecting. A PV-side breaker is selected using the panels’ electrical ratings and string arrangement; an inverter’s AC breaker is selected using its maximum continuous AC output current. The circuit between a charge controller and a battery has its own requirements.
For an AC output circuit that requires a 125% sizing allowance, a 20A maximum continuous inverter output gives a 25A calculation. That rule does not, by itself, select the breaker between solar panels and an MPPT charge controller.
Start with the breaker location
Before calculating amperage, identify the equipment on each side of the breaker.
| Circuit | Starting point for sizing | Other essential checks |
|---|---|---|
| Solar panels or PV combiner → charge controller or inverter DC input | Module short-circuit current, or Isc, and the number of parallel strings feeding that circuit | Need for string protection, module protection limits, cold-weather open-circuit voltage, cable rating and DC device configuration |
| Charge controller → battery | Controller’s rated charging output and its specified battery-side protection | Cable rating, battery fault current and protective-device interrupting capacity |
| Inverter AC output → distribution board | Maximum continuous AC output current and the manufacturer’s protection requirements | Supply voltage, phases, conductor rating, panel compatibility and connection method |
These are different electrical circuits even when they belong to the same solar installation. An MPPT controller changes the relationship between voltage and current, so its PV input current and battery charging current are not interchangeable. The Victron charge controller installation manual treats battery protection and PV array limits separately.
How to size a DC circuit breaker for solar panels
For the PV circuit, start with the module datasheet. Locate Isc, Voc and the manufacturer’s maximum permitted series overcurrent protection rating. Isc is the short-circuit current; Voc is the open-circuit voltage.
With matched modules, connecting panels in series raises the string voltage, while connecting strings in parallel adds their current. A breaker protecting a combined array output therefore sees a different current from a breaker protecting one string.
The PV sizing process has four parts:
- Determine whether that circuit needs overcurrent protection. Parallel strings and other connected sources can feed fault current into a damaged string. The module limits, array configuration and applicable installation rules determine the protection required. A disconnect function and overcurrent protection are separate requirements; installing a switch does not establish that the circuit has overcurrent protection.
- Calculate the design current for that circuit. Use the relevant Isc values and the factors required by the applicable design rules and protective-device rating. A single universal multiplier does not cover every PV installation.
- Check the allowed protection range. The chosen device must carry the design current while remaining compatible with the cable and the module or equipment manufacturer’s specified protection type and maximum rating.
- Check voltage and fault interruption. A DC circuit breaker for solar PV needs a suitable DC voltage rating for the string’s maximum calculated voltage, including cold-weather Voc, and sufficient interrupting capacity for the prospective fault current. Follow its required pole arrangement, polarity and wiring diagram.
A panel’s maximum series fuse rating is a protection limit, not an instruction to install a fuse or breaker of that value in every configuration. The module manual determines the permitted protection arrangement.
Eaton’s solar circuit protection application guide illustrates why PV current factors, device ratings and conductor checks belong in the same selection process. Its worked examples use the code edition stated in that guide; use the edition adopted for the installation being designed.
What size breaker does a 400W solar panel need?
A 400W rating alone is not enough to choose the PV-side breaker. The panel’s operating voltage is different from the nominal battery voltage in many MPPT systems.
For example, the 400Wp model in this Jinko module datasheet has these ratings under standard test conditions:
| Module parameter | Datasheet value |
|---|---|
| Maximum power voltage, Vmp | 36.24V |
| Maximum power current, Imp | 11.04A |
| Short-circuit current, Isc | 11.73A |
| Maximum series fuse rating | 20A |
Connecting that module through an MPPT controller to a 12V battery does not make the module-side current equal to 400W ÷ 12V.
That calculation gives 33.3A as an idealized power-conversion estimate at a 12V output. Actual charging current depends on battery charging voltage, available PV power, conversion losses and the controller’s output limit. Battery-side protection is then selected from the controller manufacturer’s requirements and the battery circuit design.
The same distinction applies to 24V and 48V batteries. Changing battery voltage does not supply the missing PV-side protection specification.
How to calculate the inverter’s AC breaker size
Use the inverter’s maximum continuous AC output current from its datasheet or installation manual. Where the manufacturer and applicable rules require a 125% allowance, the calculation is:
Minimum calculated rating = maximum continuous AC output current × 1.25
For a simple single-phase example at unity power factor, AC current can be estimated from power:
AC current = AC output power ÷ AC voltage
Consider a 7.6kW inverter with a 240V single-phase AC output:
- Estimated output current: 7,600W ÷ 240V = 31.67A.
- With the example’s 125% allowance: (7,600W ÷ 240V) × 1.25 = 39.58A.
- A 40A breaker is a candidate, provided it meets the inverter’s instructions and the conductor, terminal and distribution-board requirements.
If the datasheet gives a different maximum continuous output current, use that value instead of the estimate. For three-phase equipment, use the specified output current rather than dividing power by line-to-line voltage alone.
Hybrid equipment can also have charging, pass-through or other operating modes that affect a circuit’s maximum current. Select its protection from the relevant installation manual rather than applying the PV export example to every operating mode.
Solar panel breaker size chart for 240V AC output
This chart illustrates the same single-phase 240V, unity-power-factor and 125% assumptions. The power column is inverter AC output, not the PV array’s DC wattage. Calculations use unrounded current values. Breaker candidates assume the listed standard ratings are available and permitted for the equipment.
| Inverter AC output | Estimated AC current | Current × 1.25 | Breaker candidate |
|---|---|---|---|
| 3kW | 12.50A | 15.63A | 20A |
| 5kW | 20.83A | 26.04A | 30A |
| 6kW | 25.00A | 31.25A | 35A |
| 7.6kW | 31.67A | 39.58A | 40A |
| 10kW | 41.67A | 52.08A | 60A |
| 12kW | 50.00A | 62.50A | 70A |
The table gives a calculation starting point. A higher standard rating is usable only when the rest of the circuit permits it. If no rating satisfies both the required current and the equipment or conductor limits, the circuit design needs to change. Manufacturer tables take precedence over a generic chart: the Fronius Primo GEN24 installation manual lists recommended and maximum AC protection ratings by model and supply voltage.
Is a 20A or 30A breaker enough?
Under the same 125% AC assumptions:
- A 20A breaker corresponds to up to 16A of continuous inverter output, approximately 3.84kW at 240V and unity power factor.
- A 30A breaker corresponds to up to 24A of continuous inverter output, approximately 5.76kW under those conditions.
These figures do not describe a 20A or 30A PV-side DC breaker, and they do not specify the permitted cable size. The inverter’s maximum output current and the circuit checks determine which option is usable.
Match the breaker to the cable and connection point
Cable selection depends on conductor material, insulation, installation method, terminal temperature rating, ambient temperature and grouping. A list that pairs breaker amperage with one AWG size cannot capture all of those conditions.
The conductor needs adequate corrected ampacity for the circuit and appropriate overcurrent protection. Voltage drop is a separate check, especially on longer runs; there is no single cable length at which every solar circuit needs the same increase in wire size.
For a grid-connected AC circuit, the distribution board also limits how generation can be connected.
When does the 120% busbar rule apply?
One U.S. load-side interconnection method uses a 120% busbar allowance with the required supply arrangement, including power sources at opposite ends of the busbar. The main breaker rating plus 125% of the combined continuous inverter output current must fit within that allowance. For a 200A busbar with a 200A main breaker:
200A × 1.20 − 200A = 40A
Here, 40A is the allowance for the 125% term. With one inverter, it corresponds to a maximum continuous output current of 40A ÷ 1.25 = 32A under this method. The actual breaker still has to meet the inverter and circuit requirements.
This is one connection method, not a universal permission for every 200A panel. SolarAPP+ describes the conditions for different interconnection methods, including checks on panels supplied by both utility and additional power sources.
Adding a subpanel does not automatically remove an upstream busbar constraint. An installer needs to evaluate the complete connection arrangement, panel labels and locally adopted rules.
Common questions about solar circuit breakers
Can I use an AC circuit breaker on the PV side?
An AC-only rating does not establish suitability for a DC circuit. Use a device with the required DC rating and application approval, following its pole configuration and polarity instructions. Likewise, a PV-rated protective device is not automatically suitable for a battery circuit with a different prospective fault current.
Should I fit a larger breaker if the existing one trips?
A trip needs investigation before the rating changes. Possible causes include an incorrect current allowance, excessive temperature, a connection problem, a fault or unsuitable equipment. Increasing the rating without checking the conductors and equipment can remove the protection the circuit depends on.
Prepare the information for a breaker selection
For a project enquiry, collect the module and inverter or charge controller models, a simple circuit diagram, the string arrangement, cable details and installation location. That allows the protection requirements to be checked at the correct point in the system.
You can contact GEYA about the circuit requirements with that information. The selected device and installation arrangement should be checked by a qualified electrical professional against the equipment instructions and locally adopted rules.
