Why Arc Detector Breakers Are the Key to Fire Prevention

What scares PV power plant operators most isn’t power loss on cloudy days—it’s fires caused by DC arcs! The DC-side voltage of PV systems is always above 1000V. Once wires age or connectors loosen, the resulting DC arcs become extremely dangerous: they burn components, destroy combiner boxes, and can render hundreds of thousands of baht worth of equipment useless in minutes. Fortunately, PV-specific Arc Detector Breakers are designed specifically to eliminate this hazard. Today, we’ll explain why they’re the cornerstone of fire prevention for PV power plants.

First: How Dangerous Are PV DC Arcs? Ordinary Breakers Can’t Withstand Them!

Don’t assume ordinary breakers can prevent arcs—PV DC-side arcs are very different from AC arcs in homes:

• AC arcs have a "zero-crossing point," which allows them to extinguish on their own.

• DC arcs have no such "buffer." Once ignited, they’re like lit gasoline—burning hotter and spreading along wires.

For example: If the wiring of a string of modules in a power plant loosens, the increased contact resistance creates a tiny DC arc. First, it blackens the terminal connectors; then, it ignites the insulating materials inside the combiner box. Without timely power cutoff, the entire string of components could catch fire.

Ordinary breakers only protect against overloads and short circuits. DC arcs don’t draw enough current to trigger them—by the time a fire is detected, it’s already too late. For this reason, installing PV-specific Arc Detector Breakers is a non-negotiable baseline for PV power plants.

How Do PV-Specific Arc Detector Breakers Work? They Detect DC Arcs Precisely and Cut Power in Seconds!

Arc Detector Breakers for PV scenarios are purpose-built for DC arcs. Their core capability lies in "focusing on DC arc signals":

• They continuously monitor the current waveform of each module string. Whether it’s a weak arc from a hidden crack in a module or a strong arc from poor wiring in a combiner box, the breaker identifies it accurately—without confusing it with normal inverter signals.

Once a fault is detected, it cuts off the current in 0.05 seconds and triggers the "rapid shutdown" function, lowering the voltage of the faulty module string to below 30V (a safe level). In a recent test at a 10MW power plant in Chiang Mai, we simulated loose module wiring to generate an arc. Fonrich’s Arc Detector Breaker cut power instantly—even the insulating paper inside the combiner box didn’t heat up. This is far faster than the 1-second cutoff required by national standards, leaving no chance for a fire to start.

Additionally, it won’t "trip blindly." PV power plant current fluctuates significantly during the day. Fonrich’s breaker uses a specialized AI algorithm to distinguish between "normal current fluctuations" and "fault arcs." Last summer, a power plant was struck by lightning, causing current instability—but the breaker didn’t trip erroneously. A standard breaker would have shut down the system unnecessarily, resulting in significant power loss.

Third: For PV Power Plants, These 3 Scenarios Must Be Fully Protected!

1. String-Level Protection: Equip Every String to Avoid "One Fault Ruining the Whole Set"

Each module string in a power plant is an independent circuit. If one string develops an arc without a dedicated breaker, the entire string shuts down—and nearby strings could even burn. Fonrich’s string-level Arc Detector Breaker is compact enough to fit directly into combiner boxes. Equipping one per string ensures that only the faulty string is cut off; other strings continue generating power, so a minor fault won’t disrupt overall output.

Last year, the wiring of the 5th string at a power plant was chewed by rats. Fonrich’s breaker immediately cut power to that string. Maintenance technicians repaired and replaced the wiring the same day, with no impact on other strings’ generation. Without this protection, the entire inverter would have needed to shut down, resulting in the loss of thousands of kWh of electricity.

2. Inverter DC-Side Protection: Safeguard the Plant’s "Heart"

The inverter is the critical core of a PV power plant. If arc-containing current reaches the inverter’s DC side, it can easily burn the inverter’s IGBT modules—replacing one costs hundreds of thousands of baht. Installing Fonrich’s Arc Detector Breaker at the inverter’s DC input cuts off power before the arc reaches the inverter, acting as an extra "shield" for this vital component.

At a commercial power plant in Bangkok, aging cables between the combiner box and inverter created an arc. The breaker cut power instantly, leaving the inverter undamaged. Without this protection, the inverter would have been ruined, requiring at least half a month of downtime for repairs.

3. Energy Storage Integration: Dual Protection for DC Sides to Avoid Spreading Risks

Many power plants now include energy storage systems, which also face DC arc risks on their DC sides. Fonrich’s Arc Detector Breaker can link with energy storage systems: if an arc is detected in the wiring between PV and storage, it cuts off power to both the PV and storage DC circuits simultaneously, preventing faults from spreading to either side. During a recent incident at a PV-storage hybrid plant, loose wiring in the storage battery triggered the breaker—power was cut off to both systems, and the fault didn’t spread to the PV side, saving significant trouble.

When Choosing PV-Specific Arc Detector Breakers, Focus on These 3 Criteria—Fonrich Meets All of Them!

1. DC High-Voltage Compatibility: Must Withstand 1500V

Most large-scale PV power plants now use 1500V systems. The breaker must withstand this high voltage (supporting 1500V DC) and maintain insulation integrity—even during voltage fluctuations, it won’t leak electricity. This makes it far more reliable than standard models that only handle 1000V.

2. Strong Weather Resistance: Suitable for Outdoor Environments

Outdoor PV equipment endures 60℃ rooftop temperatures in summer and heavy rains in the rainy season. Fonrich’s Arc Detector Breaker has an IP68 protection rating (dustproof and submersible), and its housing uses UV-resistant materials. In high-temperature, high-humidity regions like Thailand and Malaysia, it remains undamaged for 5 years—unlike ordinary breakers, whose housings become brittle after just 2 years.

3. Integration with Monitoring Platforms: Fast Fault Localization

Large power plants make fault-finding difficult. Fonrich’s Arc Detector Breaker connects to the SafeSolar monitoring platform: via your phone, you can see which string had an arc, when power was cut off, and how long the outage lasted. Maintenance technicians don’t need to check combiner boxes one by one—they can locate the fault directly, drastically speeding up repairs. Last year, a fault occurred at a power plant in the middle of the night: the technician saw the faulty string on his phone while still in the dorm, and fixed it in just 30 minutes the next morning.

Related Q&A

Q: If a PV power plant has Arc Detector Breakers installed, do we still need other fire-fighting equipment?A: We recommend using them together with Fonrich DC Optimizers. The optimizer provides module-level arc protection, while the breaker covers string-level and inverter-side protection—this "dual protection" setup is optimal.

Q: When retrofitting an old power plant, do we need to modify the original circuit?A: No major modifications are needed! Fonrich’s Arc Detector Breaker has the same size as ordinary DC breakers used in combiner boxes. You can directly replace the original DC breaker, as the wiring method is identical. Technicians can retrofit one string in half a day, without shutting down the entire inverter—making it ideal for old power plant upgrades.