Arc Detection in Solar PV Systems: Essential Implementation Guide

Everyone in the PV industry knows that DC arcs are the "invisible bombs" of power plants—they can be caused by cracked modules, loose wiring, or even rats chewing through cables. Once an arc occurs, a fire will break out if not handled promptly. However, choosing and installing arc detection equipment isn’t a random task. Today, we’ll break down the details with Fonrich equipment, which works for both new power plants and retrofits of old ones.

First: Clarify "Which Level" of Arc Detection Your Plant Needs—Don’t Install It in the Wrong Place!

Arc detection for PV systems is divided into 3 levels. Where to install them and how many to use depends on the plant’s scale and structure—don’t follow others blindly:

1. Module-Level Detection: Priority for Small Plants/Rooftop PV, Down to Each Panel

If you have a residential PV system or a small industrial plant (under 100kW) with densely arranged modules and frequent shading, module-level arc detection is recommended. This means equipping each panel with an optimizer that has built-in arc detection, such as Fonrich’s DC Optimizer. It not only addresses shading issues but also monitors arc risks for individual panels in real time.

Advantages:

• Precise localization: If a panel has a problem (e.g., an arc from a hidden crack), you can pinpoint the exact panel without disassembling an entire string—maintenance is fast.

• Minimal loss: Cutting power to one faulty panel won’t affect the generation of other panels.

2. String-Level Detection: Mandatory for Medium-to-Large Plants, Protecting Each String

For ground-mounted plants, industrial plants (over 1MW), or systems with multiple long strings and extended cables, string-level arc detection breakers (e.g., Fonrich’s Arc Detector Breaker) must be installed in combiner boxes. Equip one breaker per string—if an arc occurs in a string (e.g., loose wiring, aging cables), only that string’s power is cut off.

Critical Note: Never try to cut costs by sharing one breaker across multiple strings!

3. Inverter DC-Side Detection: Required for All Plants, Guarding the "Last Gate"

Regardless of the plant’s size, a master arc detection breaker must be installed at the inverter’s DC input. This acts as a "shield" for the inverter: if arcs bypass the module-level and string-level protections, this breaker cuts power before the arc reaches the inverter—preventing damage to the inverter’s IGBT modules (which cost hundreds of thousands of baht to replace).

Fonrich’s inverter-side arc detection breaker supports 1500V high voltage, compatible with mainstream large inverters. It can be directly installed in the inverter’s DC input cabinet, requiring minimal circuit modifications.

Practical Installation: These 5 Details Must Be Done Right—Otherwise, Installation Is Pointless!

Choosing the right equipment isn’t enough; poor installation details will drastically reduce detection effectiveness. Pay special attention to these 5 points:

1. Wiring: No Reverse Connections, No Missing Wires, Clear Labeling

• For both string-level breakers and optimizers, always distinguish between positive and negative terminals—reverse connections will burn the equipment.

• Tighten all wires securely: Poor contact can cause arcs (essentially creating a hazard while installing protection).

• Label wires after installation (e.g., "String 1 – Combiner Box 1 – Breaker A") to speed up fault troubleshooting later.

Fonrich’s equipment has anti-reverse connection design—wires can’t be plugged in backwards, even for new installers.

2. Combiner Box Installation: Don’t Overcrowd the Box, Leave Adequate Heat Dissipation Space

When installing string-level breakers in combiner boxes:

• Don’t fill the box—leave at least a 5cm gap around each device for heat dissipation. High temperatures in combiner boxes during summer can prevent breakers from tripping when needed.

• If the combiner box is too small, replace it with a larger one or use Fonrich’s ultra-thin breakers (30% more space-saving than standard models).

3. Optimizer Installation: Don’t Block Heat Vents, Mount Near Module Junction Boxes

• Install module-level optimizers on the module brackets, ensuring heat vents are not blocked (overheating reduces efficiency).

• Mount optimizers as close to the module junction boxes as possible to shorten cable length—this lowers line losses and arc risks.

Fonrich’s optimizers have a snap-on design—they can be directly clipped onto brackets without drilling. Technicians can install 10 optimizers in half an hour.

4. Grounding: Must Be Connected to Prevent Leakage and Electric Shock

• Connect the grounding terminals of all arc detection equipment to the plant’s grounding grid, ensuring the ground resistance is below 4 ohms.

• Without proper grounding, equipment leakage can cause electric shock, and detection signals will be disrupted (this is non-negotiable).

After installation, use a ground resistance tester to verify compliance—don’t skip this step.

5. Linkage Commissioning: Connect to Inverters and Monitoring Platforms, Don’t Work in Isolation

Arc detection equipment isn’t standalone; it must link with inverters and monitoring platforms:

• When an arc is detected, the equipment should not only cut power but also send a signal to the inverter to shut down.

• It should also trigger an alert on the monitoring platform to notify maintenance staff.

Fonrich’s equipment is directly compatible with mainstream inverters (Huawei, Sungrow, GoodWe) via Modbus protocol. It connects to the SafeSolar monitoring platform, allowing you to view which string has a fault and when power was cut off—all from your phone, no need to visit the site.

Related Q&A

Q: When retrofitting an old power plant with arc detection, do we need to shut down the entire plant? How does it affect power generation?A: No need to shut down the entire plant! Retrofit in batches: For example, first shut down Strings 1–5, install string-level breakers, commission them, and restart those strings. Then move on to Strings 6–10. This way, only a few strings are offline each day, minimizing generation loss. Fonrich also has experience with "live retrofits" (under proper safety precautions).

Q: Will module-level optimizers be too expensive for residential PV systems?A: Actually, they offer great value! Residential PV systems are on rooftops, where fire risks are high. The cost of adding an optimizer per panel (around 100+ THB) is far less than the cost of repairing a roof or replacing equipment after a fire. Additionally, Fonrich’s optimizers increase power generation by 15%—the extra income covers the optimizer cost in just over 6 months. It’s both safe and profitable.

Q: What should I do if the arc detector trips due to an arc?A: 1. First, use the monitoring platform to locate the faulty string/panel.2. Shut down power and inspect the site:

• If a module-level optimizer tripped, check the corresponding panel for hidden cracks or a burnt junction box.

• If a string-level breaker tripped, check the string’s cables for damage or loose connectors.

3. After repairs, reset the equipment via the monitoring platform. Fonrich’s platform has a "one-click reset" function—no on-site operation needed.