How to Calculate Fuse Sizes for Photovoltaic Installations

Every photovoltaic (PV) power application must use fuses that are properly sized to its system. When you use the incorrect fuse size (or a standard non-PV fuse), you put the system's reliability and safety in jeopardy. Due to the explosive growth in PV system power, understanding how to properly size a fuse for a PV application is essential. 

This paper provides insight into how fuse sizes affect PV applications, and how to calculate the correct fuse size for PV equipment. This paper will go over NEC's method for how to size a fuse to a PV system. There are other methods, such as that found in IEC 60269-5-19, Low-voltage fuses - Part 5: Guidance for the Application of Low-Voltage Fuses. If you are interested in using a different method, contact the Littelfuse Techline

Fuses can only provide proper protection against reverse currents and circuit faults (which can cause personnel injury, power outages, equipment failure, and property damage) if they are the correct size for the system. The maximum circuit current and system voltage are important factors to determine which fuses can protect these systems. PV applications require fuses that can protect against overcurrents, reverse currents and short circuits, against which standard fuses would not provide adequate protection. Therefore, you must use fuses that are specifically designed for PV installations.

This document will you understand the formulas to use when determining the right fuse size for your system.