Quick Answer
You should select a combiner box rated for your maximum DC system voltage, which is typically the PV array maximum voltage, not the string maximum voltage. A common approach is to add 10-20% to the maximum PV array voltage to account for any potential voltage spikes.
Choosing the Right Combiner Box Rating
When selecting a combiner box, it’s essential to consider the maximum DC system voltage, which is typically the PV array maximum voltage. This is usually determined by the maximum voltage of any single PV module in the array. For most residential solar systems, the maximum PV array voltage is around 600-700V DC. However, when using larger solar panels (e.g., 72-cell or 96-cell), the maximum PV array voltage can exceed 700V DC.
Calculating Combiner Box Rating
To calculate the combiner box rating, consider adding 10-20% to the maximum PV array voltage to account for any potential voltage spikes. For a 600V DC PV array, a suitable combiner box rating would be 660-720V DC. Using a higher-rated combiner box ensures safe operation and reduces the risk of overheating or electrical stress on the components.
Combiner Box Selection Process
When selecting a combiner box, ensure it meets the following requirements:
- Rated for the calculated maximum DC system voltage
- Compatible with the number of strings and modules in the array
- Meets or exceeds the required current rating (based on the total DC system current)
- Compliant with local electrical codes and regulations
- Offers adequate overcurrent protection and arc fault detection
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