A combiner box contains a variety of protective components that reduce the risk of electrical faults, transient overvoltages, and equipment damage.
A typical solar combiner box contains fusíveis, surge protective devices (SPDs), disjuntores, and isolation switches, while auxiliary accessories include busbars, terminal blocks, and PV connectors.
Understanding the purpose of each component helps clarify the internal structure of a solar combiner box and the electrical connections among the components.
Main Components Inside a Solar Combiner Box
Fuses
A fuse protects each solar panel input circuit and prevents overcurrent from damaging equipment.
When multiple circuits are connected in parallel and one of them develops a fault, the other healthy circuits may feed reverse current into the faulted circuit. When the reverse current exceeds the fuse’s operating threshold, the fuse element melts and cuts off the faulted circuit. The role of the fuse is to limit the overcurrent and reverse current that the faulted solar panel circuit is exposed to. It should be noted, however, that not every PV circuit must have its own fuse.
Whether a fuse is needed depends on how much reverse current the other circuits may feed into the faulted circuit, and this current value is then compared with the reverse overcurrent limit that the solar panel can withstand (that is, the maximum series fuse rating). If the former may exceed the latter, a fuse is needed; if it will not exceed it, no fuse is required.
Surge Protective Devices
A surge protective device protects the PV circuit from transient overvoltages, especially transient overvoltages caused by lightning-induced surges and electrical switching operations.
When a surge occurs, the SPD temporarily forms a low-impedance path that directs the surge current to the grounding system, thereby limiting the overvoltage at the equipment terminals. Common PV DC SPDs include:
- Type 1 SPD: Used when the lightning protection design requirements of the installation environment call for protection against partial direct lightning current.
- Type 2 SPD: Mainly used to protect against induced lightning surges and transient overvoltages generated by switching operations.
- Type 1+2 SPD: Combines the protective functions of Type 1 and Type 2.
YRO surge protective devices use replaceable protection modules. When a protection module reaches the end of its service life or fails, it can be replaced separately without replacing the entire SPD.
Circuit Breakers
A circuit breaker is another common protective device in a combiner box and provides overload and short-circuit protection for the circuit.
Unlike a fuse, a circuit breaker can be manually reset and put back into service after the fault is cleared, whereas a fuse must have its fuse element replaced before it can continue to provide protection.
Isolation Switches
An isolation switch is mainly used to disconnect a section of the circuit from other electrical equipment, providing isolation conditions for equipment inspection, maintenance, or repair. Although both an isolation switch and a circuit breaker can be used to disconnect a circuit, their main functions differ. An isolation switch focuses on electrical isolation, while a circuit breaker can also perform the corresponding overcurrent protection task.
Terminal Blocks and Connectors
Terminal blocks and connectors are used to connect electrical circuits inside and outside the combiner box.
They can be used in the following locations:
- Connections between solar panel input circuits and the combiner box.
- Connections between busbars and main output circuits.
- Connections between input circuits and output circuits.
- Connections for grounding circuits and auxiliary monitoring circuits.
Terminals and connectors used at different locations may have different structures. During installation, ensure that the conductors match the terminals and that crimping and tightening are completed as required.
Busbars
A busbar connects multiple input circuits and collects the current from each circuit before transmitting it to the output.
Inside a combiner box, a busbar can reduce the wiring complexity caused by directly connecting multiple conductors, and make the electrical connections more centralized and clearer.
Common busbar materials include copper and tin-plated copper. Depending on the internal structure of the combiner box, busbars can adopt different shapes and mounting methods to suit the connection requirements among different components.
The busbar layout also affects the internal wiring space, maintenance convenience, and current transmission path.
Enclosure
O enclosure houses and protects the electrical components inside the combiner box and provides space for wiring connections and component installation.
Common materials include ABS, PC, and metal, and different materials suit different installation environments and product structures.
The enclosure design needs to consider the installation space for internal components, cable entry and exit positions, heat dissipation conditions, and subsequent maintenance requirements.
For combiner boxes installed outdoors, dust, water, ultraviolet radiation, and temperature changes also need to be considered according to the actual environment.
How Do the Components Inside a Combiner Box Work Together?
The components inside a combiner box work together according to their electrical connections to complete power collection, circuit protection, and output. The basic working process can be summarized in the following steps:
- Input circuit connection: Multiple cables are connected to the combiner box through input terminals or connectors.
- Input circuit protection: Circuits that require independent overcurrent protection pass through the corresponding fuses or other protective devices.
- Current collection: Each circuit is connected to the corresponding busbar to collect the electrical energy together.
- Surge protection: SPDs are connected between the protected circuit and the grounding system as designed to limit transient overvoltages.
- Main circuit control and protection: Depending on the product configuration, the corresponding protection, operation, or isolation functions are achieved through circuit breakers or isolation switches.
- Power output: The collected electrical energy is delivered to downstream equipment through output terminals or connectors.
Note: The arrangement and connection methods of the components in an actual combiner box may differ, and the product’s electrical schematic diagram and wiring diagram should be taken as the authoritative reference.
Conclusão
A solar combiner box generally contains connecting components, protective components, and an enclosure structure. Fuses, SPDs, circuit breakers, and isolation switches perform different protection or operating tasks, while busbars, terminal blocks, and connectors complete the electrical connections and power collection.
The internal configuration of different combiner boxes may vary considerably. Understanding the role of each component and its connection relationships, helps procurement and installation personnel determine whether the product structure meets the actual project requirements.
