Quick Answer
To calculate the right fuse size for solar panels, determine the short circuit current (Isc) of the panel and divide it by the safety factor (typically 1.25) to get the fuse rating. Multiply the fuse rating by the number of panels in parallel to get the required fuse size. Add 20% to the fuse size for future expansion.
Determining Short Circuit Current (Isc)
The short circuit current (Isc) of a solar panel is the maximum current the panel can produce when all cells are short-circuited. Check the panel’s datasheet or specifications to determine the Isc value. For example, a 300W solar panel with an Isc of 8.5A.
Calculating Fuse Rating
Using the example above, divide the Isc value (8.5A) by the safety factor (1.25) to get the fuse rating: 8.5A / 1.25 = 6.8A. This means a 6.8A or 7A fuse would be suitable for this panel. However, since fuses are typically available in standard sizes, round up to the nearest standard fuse rating, which is 7.5A or 8A in this case.
Choosing the Right Fuse Size
When multiple panels are connected in parallel, the total Isc value increases. For example, if 4 panels are connected in parallel, the total Isc would be 4 x 8.5A = 34A. Divide the total Isc by the safety factor to get the required fuse size: 34A / 1.25 = 27.2A. Round up to the nearest standard fuse rating, which is 30A in this case. Consider adding 20% to the fuse size for future expansion: 30A x 1.2 = 36A. Therefore, a 40A or 50A fuse would be a suitable choice for this application.
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