Choosing a correctly sized fuse is critical for the safe, reliable, and long-term operation of photovoltaic (PV) systems. Unlike typical electrical distribution or controller-equipped applications, PV system fuses face unique constraints: prolonged environmental exposure creates abnormal ambient temperatures that impact fuse performance, conductor selection, and sizing. Additionally, unlike traditional circuits with continuous loads, PV modules require extra considerations for fuse sizing if they generate sustained current. These conditions necessitate pre-installation fuse sizing for system components.

When Are Fuses Required vs. Unnecessary?

Article 690.9(A) of the National Electrical Code (NEC) outlines requirements for protecting PV systems from overcurrent. Fuses safeguard cables and PV modules against line-to-line, line-to-ground, and mismatch faults, aiming to prevent fires and safely isolate faulty circuits during overcurrent events. However, fuses may not always be required:

1. Single series string: No fuse needed

2. Two parallel strings: No fuse needed

3. Three or more parallel strings: Fuse required

Fuse Selection for System Components

In a complete solar power system, fuses can be added between components:

· Solar array to charge controller

· Charge controller to battery bank

· Battery bank to inverter

Fuse requirements and ratings vary based on component amperage and wiring.

Solar Panel Fuses

Panels above 50W with 10-gauge wires (30A capacity) require 30A fuses when three or more are paralleled. For example, three 15A panels could deliver 40-60A to a shorted panel, exceeding the 30A wire limit. Panels under 50W with 12-gauge wiring need 20A fuses.

[Recommended Product] Weatherproof PV fuses with ceramic bodies and silver alloy elements (-40°C to 125°C tolerance), paired with modular fuse holders for outdoor durability.

Combiner Box Fuses in Parallel Systems

In parallel configurations, combiner boxes house fuses/breakers per panel. Sizing depends on worst-case current. For a 195W 12V panel with 12.23A short-circuit current (Isc), NEC requires a 25% buffer for continuous loads (15.28A per panel). Four paralleled panels could theoretically produce 61.15A, necessitating 8 AWG wire (60A capacity) and a 60A fuse/breaker.

[Recommended Product] 60A DC fast-acting fuses with 50kA breaking capacity (UL248-15 certified), offering 30% faster response for PV array protection.

Charge Controller-to-Battery Fuses

For PWM charge controllers, fuse and wire sizes match the controller’s amperage (e.g., 60A fuse for a 60A controller).

[Recommended Solution] Time-delay EVH/EVH15 fuses with slow-blow characteristics to withstand motor startup surges, paired with IP67-rated waterproof fuse holders.

Battery-to-Inverter Fuses

The battery-inverter connection carries the highest current. A 600W 12V pure sine inverter drawing 50A continuously requires 6 AWG wire and a 50-60A fuse.

Technical Value-Added Services

Our engineers provide free system current calculations based on your component parameters (Isc, array configuration, wire specs) to design cost-effective fuse solutions. Proper fuse selection enhances safety and extends equipment lifespan. Contact our PV technical team for customized protection plans and product recommendations.