As photovoltaic (PV) systems move toward higher voltages and larger capacity, the proper choice of fuses --an important component of DC protection system --directly affects the safety, stability and service life of the entire PV system. If the rated current of the fuse is too low, it may explode frequently because of normal operating currents. Conversely, if the rated current is too high, the fuse may not be able to interrupt the circuit in time for the fault to occur, causing damage to equipment or even a safety incidents. Therefore, the correct selection of rated current and voltage of PV fuses is an important step in the design of PV systems.
Why choose the right PV fuse?
Solar PV systems consists mainly of PV assembly, combiner boxes, inverter, energy storage device and related protective device. Because photovoltaic arrays produce direct current (DC) --which, unlike AC, does not naturally cross zero --the arc is harder to extinguish in the event of a short circuit or overcurrent fault. Therefore, PV systems require specially designed DC PV fuses rather than standard AC fuses.
Appropriate fuse selection can achieve the following objectives:
Fast break short circuit fault, protect PV assembly and fiber optic cable;
Prevent fault currents escalation and reduce fire risks.
Improve the operational reliability of inverters and combiner equipment;
Reduce maintenance costs and extend the system's overall service life.
How is the rated current selected?
Rated current is one of the most important parameters of PV fuse. Short-circuit current, ambient temperature and continuous operating conditions of the photovoltaic assembly should be considered in the selection.
In general, the rated current of the fuse should exceed the maximum operating current of the PV module while maintaining a certain safety margin. The industry generally follows this principle:
Fuze rated current ≥ 1.25 × PV Module short circuit current (Isc)
For example, if a module has a short-circuit current of 13A, the calculation value is:
13A × 1.25 = 16.25A
In this case, a a 20A PV fuse rather than a a 15A model usually chosen to avoid disruptive tripping during normal operation. If the system is installed in a high temperature environment, the fuse's current-carrying capacity will decrease as the temperature increases; therefore, adjustments require to be made to the manufacturer's temperature derating curve. This is particularly important for projects in locations such as deserts or roofs exposed to high temperatures.
In addition, for photovoltaic arrays with multiple parallel strings, an inverse current must be considered. If one segment fails, another parallel segment may inject a large amount of reverse current into the fault segment; consequently, the fuse must be able to handle normal operating currents while blowing rapidly in the event of a reverse fault current.
How to select rated voltage?
In addition to current parameters, rated voltage is equally important.
The rated voltage of the PV fuse shall be equal to or greater than the maximum DC voltage that may occur in the system. Otherwise, while fuses may explode, they may not be effective in extinguishing the DC arc and pose a serious safety hazard.
Current voltage levels commonly used in PV systems include:
600V DC
1000V DC
1500V DC
In recent years, large ground-installed power plants are increasingly using 1500V DC systems to reduce line losses and cable costs while increasing power generation efficiency. Therefore, for 1500V systems, a dedicated PV fuse with a rating of 1500V DC must be selected; a 1000V products cannot be used as an alternative.
In practical selection, the the system's open-circuit voltage (Voc) should be calculated, taking into account local minimum ambient temperature. Because low temperatures can lead to higher module output voltage, designers typically use maximum open circuit voltages --adjusted to the lowest ambient temperature --as the basis of their selection to ensure that fuses operate safely in extreme conditions.
What other technical parameters require attention?
In addition to rated current and rated voltage, the following factors should be taken into account:
Broken capacity
Disconnection capability is the maximum fault current that a fuse can safely interrupt. Large photovoltaic plants tend to experience large short-circuit currents, therefore products with sufficient fragmentation capacity should be selected to ensure reliable interruptions during failures.
Time-Current Characteristics
Special fuses for photovoltaic cells typically have protective characteristics optimized for PV systems; they are designed to withstand normal current fluctuations caused by module startup and environmental changes, while also acting quickly in the event of failure. Product Certification
High-quality photovoltaic fuses usually meet international standards such as IEC 60269-6 and UL 248-19 and are certified as TÜV and CE. These certifications demonstrate that the product has been rigorously tested to ensure greater safety, reliability and consistency.
Environmental Adaptability
Outdoor PV projects are exposed to high temperatures, low temperatures, UV radiation, high temperatures, humidity, salt mist, dust and other harsh environments. Therefore, the fuse must have excellent corrosion resistance, weather resistance and long-term stability.
Common Selection Pitfalls
During project implementation, users often make the following errors:
Use standard AC fuses rather than PV specific DC fuses;
Only select the fuse according to the rated power of the equipment and ignore the short-circuit circuit current of the module.
Select rated voltage below the maximum DC voltage of the system;
Ignore the derating of carrier capacity due to ambient temperature;
The effect of reverse current on the configuration of parallel strings is not considered.
These problems can affect the effectiveness of protection and even lead to failure of protection during failure. Therefore, the system parameters and related standards must be strictly observed in the calculation and selection process of the design phase.
Conclusion:
While photovoltaic fuses are small protective elements, they play a crucial role in ensuring the safe operation of the entire photovoltaic system. Correct selection of rated current and voltage can not only effectively protect PV components, inverters and cables, but also reduce the failure rate of the system and improve the operating efficiency of the plant. With the increasing popularity of 1500V high-voltage PV systems and large-scale energy storage projects, fuse selection will increasingly focus on high fragmentation capacity, high reliability and long-term stability. Designers should conduct a comprehensive evaluation based on system's electrical parameters, operating environment and international standards to ensure the long-term, safe and efficient operation of PV power plants.
Frequently Asked Questions
1.Can standard AC fuses be used instead of PV fuses?
No. AC fuses lack arc extinguishing ability and cannot meet the DC protection requirement of PV systems.
2.Is the higher rated current of a PV fuse safer?
No. Excessive rated current reduces the sensitivity of overcurrent protection and may prevent the circuit from being disconnected in time for failure. Therefore, the rated current should be selected appropriately in accordance with the short-circuit circuit current of the module and design specifications.
3.Why must 1500V photovoltaic systems use a 1500V fuses?
Because the fuse's rated voltage must not be lower than the system's maximum operating voltage, otherwise, the fuse may fail to effectively extinguish the DC arc after detonation, thereby endangering the safety of equipment and personnel.
