Dimensionamiento de interruptores automáticos de CC solares: string, salida del combinador y selección de MCB vs MCCB

Respuesta rápida de dimensionamiento

Dimensiona un interruptor automático de CC solar en su posición real en el diagrama unifilar. Usa la tensión de string corregida por frío_oc para la tensión, la I del módulo_sc multiplicada por el número de strings en paralelo y el factor requerido por el proyecto para la corriente; luego confirma la protección del cable, el poder de corte en CC, el cableado de los polos y la reducción de capacidad por envolvente. Elige un MCB o MCCB solo después de conocer esas funciones.

El mismo generador fotovoltaico puede requerir un dispositivo de 20 A en un string y un dispositivo de 100 A en la salida del combinador. Ambos dispositivos ven aproximadamente la misma tensión de string, pero no transportan la misma corriente ni protegen el mismo conductor. Por eso una solicitud como “interruptor solar de 1000 V CC” no está lista para la selección de modelo.

La primera pregunta no es ¿Qué tamaño de interruptor? Es ¿Dónde está el interruptor y qué puede alimentar una falla en ese punto?

Coloca el interruptor en el mapa de protección fotovoltaica

Un generador solar es una cadena de circuitos eléctricamente diferentes. Marca el interruptor propuesto antes de abrir un catálogo:

String fotovoltaico → entrada del combinador de strings → salida de CC combinada → entrada de CC del inversor

Moverse una posición hacia la derecha cambia la trayectoria de la corriente. Los módulos en serie elevan la tensión. Los strings compatibles en paralelo elevan la corriente. Un interruptor en una entrada individual normalmente transporta un string; un interruptor en la salida común transporta todos los strings conectados a esa salida.

Posición	Corriente a través del dispositivo	Función principal a establecer	Preselección habitual
String individual	Un string	Protección contra corriente inversa y aislamiento del string	Fusible gPV o MCB de CC con clasificación fotovoltaica donde el diseño lo permita
Salida del combinador	Suma de los strings en paralelo	Protección del alimentador combinado y del cable de salida	MCB de CC con clasificación fotovoltaica, MCCB de CC o seccionador con protección separada
Entrada de CC del inversor	Corriente asignada a esa entrada del inversor o trayectoria MPPT	Aislamiento del equipo y protección coordinada	Interruptor o seccionador especificado por el diseño del sistema

La tabla dice deliberadamente “preselección”. No se requiere automáticamente un interruptor automático en cada posición. Un string puede usar fusibles gPV; un inversor puede incluir ya un seccionador de CC adecuado; una salida puede necesitar aislamiento mientras la protección contra sobrecorriente se proporciona en otro lugar. Define la función faltante antes de elegir el dispositivo.

El artículo sobre dimensionamiento de cajas combinadoras solares explica cómo la agrupación MPPT determina qué strings pueden compartir una salida. Completa primero esa decisión de arquitectura. Un interruptor no puede corregir strings que nunca debieron haberse puesto en paralelo.

Establece la ventana de corriente, no solo un amperaje mínimo

El cálculo de corriente tiene dos lados. El interruptor debe soportar la corriente de diseño en las condiciones instaladas, pero no debe ser tan grande que el cable protegido o el equipo conectado quede fuera de sus límites.

Para strings fotovoltaicos emparejados:

I_sc,path = N_p × I_sc,módulo

donde:

• I_sc,path es la base de corriente de cortocircuito para la trayectoria seleccionada en amperios;
• N_p es el número de strings conectados en paralelo en esa trayectoria;
• I_sc,módulo es la corriente de cortocircuito del módulo en su condición de prueba indicada.

El método de instalación del proyecto determina entonces el tratamiento de la corriente de diseño:

I_diseño = I_sc,path × K_proyecto

K_proyecto is not a number to guess. It represents the current factor required by the adopted installation rules and design basis. North American examples commonly show 1.25 or 1.56 depending on equipment rating and the calculation path. IEC-oriented projects must use the applicable installation requirements, module data and manufacturer instructions rather than relabeling one of those figures as a universal “IEC multiplier.”

The useful selection window is:

Required carrying current ≤ usable breaker rating or setting ≤ permitted protected-circuit limit

The upper boundary may be set by derated cable ampacity, terminal rating, inverter input limit or another protected component. Selecting the next standard breaker above I_diseño is only valid when the upper boundary still passes.

Series Modules Do Not Multiply Breaker Current

Twenty modules in series do not produce twenty times the module current. They increase string voltage while string current remains based on one module. Five identical strings in parallel produce approximately five times the current. This is why dividing array watts by an assumed DC voltage is a poor substitute for the module datasheet and string schedule.

Use I_sc and I_mp for Different Checks

I_sc is the short-circuit-current starting point used in PV overcurrent design. I_mp describes operating current near maximum power and helps verify inverter MPPT loading and normal operation. Keep both values on the worksheet. Do not replace the protection basis with the lower I_mp, and do not forget the inverter’s operating-current limit after calculating from I_sc.

Keep IEC and North American Examples in Their Own Lanes

Eaton’s North American PV application guide, for example, distinguishes 80%-rated and 100%-rated molded-case breakers. Its worked method uses 1.56 × I_sc for an 80%-rated breaker and 1.25 × I_sc for a 100%-rated breaker, together with conductor and temperature checks. Those figures are useful inside that NEC/UL and product context. They should not be detached from it and published as a global PV rule.

For an IEC project, begin with the edition adopted by the contract or jurisdiction. The public scope of IEC 60364-7-712 confirms that it addresses PV electrical installations, but a scope page does not establish the complete calculation for a specific project. Record the actual design rule beside K_proyecto; this keeps the arithmetic reviewable and prevents a supplier from silently switching methods.

Set the Voltage Rating from Cold V_oc and the Pole Diagram

String voltage is highest when the modules are open-circuit and cold. A breaker selected from the module’s STC V_oc alone can be underrated on a cold morning.

Where the module provides a negative V_oc temperature coefficient in percent per degree Celsius, a preliminary calculation is:

V_{oc,cold,module} = V_oc,STC × [1 + |β_Voc| × (25 − T_mín)]

V_{oc,cold,string} = N_s × V_{oc,cold,module}

where N_s is the number of modules in series and T_mín is the project’s minimum design temperature. Enter −0.27%/°C as 0.0027. If the module manufacturer or adopted design method specifies another temperature calculation, use it consistently across the inverter and every DC component.

The breaker’s declared DC voltage must be at least the approved maximum circuit voltage. It must also achieve that rating in the exact pole arrangement shown by its manufacturer. Some high-voltage DC breakers place several contacts in series to share arc interruption. A four-pole body does not automatically equal a 1000 V or 1500 V breaker.

The existing JUTRION cold-string voltage calculator can provide a first-pass V_{oc,cold,string} result. It was created for PV SPD voltage screening, but the cold string voltage is also an input to breaker, isolator, cable and inverter checks.

Use the Fault Path to Decide Whether a Breaker Can Protect the Circuit

A breaker’s rated current and its breaking capacity answer different questions:

• Rated current or trip setting: can the device carry normal current and protect the circuit against applicable overcurrent?
• DC breaking capacity: can it safely interrupt the prospective fault current at the stated DC voltage and wiring condition?

Do not compare a 100 A breaker rating with a 50 A reverse-current contribution and conclude that the device can interrupt the fault. A normal-current label does not prove trip response, conductor protection or DC interruption performance.

At a string fault, healthy parallel strings may feed reverse current into the damaged string. An initial screen is:

I_{inversa,evaluación} = (N_p − 1) × I_sc,cadena

This shows why reverse-current exposure grows as more strings are paralleled. It does not by itself select a breaker or fuse. The final design must consider the module’s maximum series-fuse rating, conductor capacity, protective-device characteristic and the requirements of the adopted installation rules.

At a combined output, identify every source that can feed the fault. PV modules are current-limited compared with a utility or battery, but parallel sub-arrays, connected power-conversion equipment and any storage interface can change the available current. If batteries are connected at DC level, stop treating the circuit as a PV-only example; battery fault-current assessment deserves its own design.

Do Not Assume a Large Breaking Number Solves a Poor Trip Decision

A breaker may have ample ultimate interruption capacity and still fail to protect the intended conductor because its trip threshold or time-current response is unsuitable. Conversely, a low-current breaker can have a normal rating close to the load yet lack the required DC breaking capacity at the actual voltage. Verify both the interruption rating and the protective characteristic.

PV faults can also occur near the lower end of a breaker’s operating range. Selectivity between string devices and an output breaker is not guaranteed simply because the output device has the larger ampere label. Use manufacturer coordination data where selective operation matters, and treat the claimed trip curve as model-specific evidence rather than a generic “C-curve for solar” rule.

IEC 60947-2:2024 applies to circuit breakers for instructed or skilled persons with rated voltages up to 1000 V AC or 1500 V DC. That product-standard scope supports the key procurement rule: obtain verified DC ratings for the exact breaker, not an AC breaking figure or a family-level marketing label.

Choose DC MCB or DC MCCB After the Duty Is Visible

“Use an MCB below 63 A and an MCCB above 63 A” is convenient, but it is not a universal engineering boundary. Product ranges overlap. Some DC MCB families extend above 63 A; some projects choose an MCCB at a lower current because they need a different breaking capacity, adjustable protection, larger terminals or accessories.

Project need	DC MCB is the stronger shortlist when…	DC MCCB is the stronger shortlist when…
Formato de instalación	A compact DIN-rail device fits the string or small feeder	A molded-case panel device, larger conductors or busbars are involved
Protection adjustment	The declared fixed characteristic suits the circuit	An available adjustable trip unit helps coordinate the feeder
Breaking duty	The model’s verified DC breaking capacity exceeds the fault level	The circuit requires a higher verified DC interruption duty
Control and indication	Basic handle position or modular auxiliary options are sufficient	Shunt trip, auxiliary contacts or remote operation are required and supported
Typical PV position	Individual string or lower-current branch	Combiner output or higher-current array feeder

The decision is not about which family is “better.” It is about which verified product satisfies the location’s current window, voltage/pole arrangement, interruption duty, cable interface and control requirements. After those values are known, compare the available JUTRION DC MCB configurations y los JUTRION DC MCCB configurations.

Decide Whether the Location Needs a Fuse, Breaker or Isolator

Three devices often appear in the same combiner box, but their jobs are not interchangeable.

• gPV fuse and holder: provides PV string or array overcurrent protection within its verified duty. It does not provide maintenance isolation unless the complete fuse-switch arrangement is designed for that function.
• interruptor automático de CC: provides automatic overcurrent operation plus switching within its declared ratings. It does not automatically satisfy a required isolating function unless it is declared suitable for isolation.
• DC switch-disconnector: provides manual load switching and isolation within its utilization rating. It does not provide automatic overload or short-circuit protection.

At string level, gPV fuses are common because parallel strings can feed reverse current into a faulted string and the module provides a maximum series-fuse rating. A resettable breaker may be useful where its PV duty and characteristic are verified, but “resettable” is not evidence that it coordinates better.

At a combiner output, a breaker may protect the combined cable and provide switching. Another design may use a switch-disconnector because overcurrent protection is located elsewhere. State which function the device performs; otherwise two suppliers can quote different architectures under the same “DC breaker” request.

Coordinate the Breaker with the Complete DC Path

A correct breaker can still be wrong in an incorrectly coordinated system. Complete five checks before freezing the model.

Cable

Verify conductor ampacity after ambient-temperature, grouping, installation and termination corrections. The breaker rating or setting must remain within the permitted protection relationship. Do not increase the breaker solely to stop nuisance trips without reviewing the enclosure temperature and cable.

Inverter

Compare cold string voltage with maximum DC input voltage. Compare the parallel-string operating current with the MPPT/input-current limit, and total I_sc with the inverter’s permitted short-circuit current. The breaker does not authorize an array that exceeds the inverter data.

String fuses

Confirm whether each string needs reverse-current protection and whether the selected fuse/link remains below the module maximum series-fuse rating while carrying the required current under enclosure conditions. The common output breaker and string fuses normally protect different conductors.

SPD de CC Fotovoltaico

An SPD limits transient overvoltage; it is not the normal overcurrent device. Follow the SPD manufacturer’s backup-protection instructions and check its short-circuit behavior. The guide to selecting a DC SPD for solar PV covers U_CPV, Type 2/Type 1+2 and protection-level decisions.

Enclosure and assembly

Outdoor combiner boxes can run substantially hotter than the surrounding air. Use the breaker’s actual temperature/altitude data, terminal limits and mounting instructions. Closely spaced protective devices, solar heating, cable losses and restricted airflow all affect usable current. Review the complete PV combiner-box assembly, not only the breaker nameplate.

If a catalogue curve shows that the breaker carries less current at the expected internal temperature, apply that curve before choosing the frame. If no applicable curve or assembly data is available, increasing the breaker rating by an improvised percentage is not a defensible thermal design. The larger breaker may also require a larger conductor, terminal or enclosure and may no longer protect the original cable.

IEC 62548-1:2023 covers PV array design requirements including DC wiring, electrical protection devices, switching and earthing provisions. IEC 60364-7-712:2025 applies to electrical installations of PV systems. These installation contexts are distinct from the circuit-breaker product standard.

One Array, Three Different Breaker Decisions

Illustrative design: each string has 20 identical modules. Module data states V_oc,STC = 41.8 V, I_sc = 14.2 A and β_Voc = −0.27%/°C. The minimum design temperature is −20°C. Five compatible strings feed one inverter input through a combiner. For this example only, the project’s preliminary current method uses 1.25 × I_sc.

First, establish the common voltage duty

Cold module V_oc = 41.8 × [1 + 0.0027 × (25 − (−20))] = 46.88 V

Cold string V_oc = 20 × 46.88 = 937.6 V

The strings are in parallel at the combiner, so their voltages do not add. The string device and the output device both require a verified voltage/pole arrangement above the approved maximum circuit voltage. A 1000 V DC class is the initial shortlist, subject to the project’s additional voltage treatment and the exact breaker diagram.

Position 1: one string

Preliminary string design current = 14.2 × 1.25 = 17.75 A

A 20 A PV-rated protective device is the first current candidate. Before choosing a DC MCB, compare this result with the module maximum series-fuse rating, conductor ampacity, required reverse-current protection and the exact trip characteristic. A gPV fuse may remain the better string-protection choice.

With five strings in parallel, the four healthy strings produce an initial reverse-current screen of:

(5 − 1) × 14.2 = 56.8 A

That figure explains why string protection deserves attention. It does not mean a 56.8 A string breaker should be fitted.

Position 2: combiner output

Total I_sc = 5 × 14.2 = 71.0 A

Preliminary output design current = 71.0 × 1.25 = 88.75 A

A 100 A-class DC breaker is a current shortlist for the combined output. The handoff from MCB to MCCB now depends on the available product range, verified DC breaking capacity, required settings, terminal size and enclosure temperature—not on a universal 63 A rule.

Position 3: inverter input

The current arithmetic may be identical to the combiner output because it is the same feeder. The decision is not automatically identical. Confirm whether the inverter already provides a DC switch, whether an external breaker is required, the maximum input current and I_sc, the permitted switching arrangement and the location needed for safe maintenance.

Posición	Calculated current starting point	Initial device direction	Decision that remains
Un string	17.75 A	20 A PV protective device candidate	gPV fuse or DC MCB; module/cable coordination
Salida del combinador	88.75 A	100 A-class DC breaker candidate	MCB/MCCB, DC breaking capacity, settings and temperature
Inverter input	Same feeder current	Breaker or switch-disconnector as required	Inverter limits and whether protection already exists

The calculation has produced three different functional decisions from one array. That is more useful than quoting one breaker size for “a 100 kW solar system.”

Read the Breaker Datasheet as a Connected Rating Set

Do not approve the device by circling one number. Read these ratings together:

• U_e: rated operational voltage for the stated DC pole arrangement;
• I_n or frame/setting: current rating and available adjustment under reference conditions;
• DC breaking capacity: declared interruption performance at the relevant DC voltage;
• trip characteristic: how and when the device operates, not simply a B/C/D letter borrowed from another family;
• isolation declaration: whether it can serve the required isolating function;
• pole and polarity diagram: the only valid connection for the declared high-voltage rating;
• temperature and altitude data: the basis for usable current in the real enclosure;
• terminals: conductor range, material, preparation and tightening torque;
• accessories: auxiliary contacts, shunt trip or remote operation where the system needs them.

A label such as “4P, 1000 V DC, 100 A” does not disclose the complete connected rating set. Ask for the exact technical sheet and wiring diagram for the ordered model.

Three Datasheet Warning Signs

• One breaking-capacity number with no DC voltage: interruption performance must refer to a stated voltage and test arrangement.
• A 1000 V claim with no pole diagram: the buyer cannot confirm how the arc chambers share voltage or where the conductors connect.
• One current rating with no reference temperature: the rooftop enclosure duty remains unknown.

These omissions do not automatically prove that a product is unsuitable, but they prevent an engineering selection. Resolve them before the device is installed in a live PV string.

Preguntas Frecuentes

Complete the Selection at Each Position

For an individual string, resolve reverse-current protection and the module’s series-protection limit. At the combiner output, resolve combined current, cable protection and DC breaking duty. At the inverter input, resolve the equipment limits and the required isolation point.

Only then choose the product family. A compact MCB de CC may fit the string or smaller feeder; a MCCB de CC may better fit the combined output. The final model is the one whose current, voltage, interruption, poles and installed-condition ratings all refer to the same circuit—not five individually impressive numbers collected from different conditions.