How a Commercial PV Installer Cut Arc-Fault Downtime by 85% with a DC AFCI Combiner Box

2026-08-05 0 Leave me a message

Customer Background

A regional commercial solar EPC company, based in Arizona, specializes in rooftop and ground-mount PV systems for warehouses and distribution centers. The company installs roughly 25 MW per year, with typical projects ranging from 500 kW to 3 MW. Their clients are logistics operators and cold-storage providers who need reliable solar assets with minimal power interruptions.

Challenges with Standard Combiner Boxes and Inverter-Level AFCI

For years, the installer used standard DC combiner boxes with only fuses and a DC disconnect. Arc fault protection was handled at the inverter level, but this caused two recurring problems. First, inverter-level detection could not isolate which string or combiner box had a fault, forcing crews to check every connector on the roof. Second, the inverters generated false trips during grid switching and inverter startup, shutting down the whole array.

The most serious incident involved a loose connector inside a combiner box that created a series arc fault. The arc smoldered for weeks before a thermal inspection caught it. That event caused a fire and triggered a six-figure liability claim. The EPC team knew they needed arc fault protection closer to the source, but retrofitting external AFCI modules onto existing combiner boxes was expensive and complicated. Each module required separate wiring, enclosures, and coordination with the inverter.

Why the Soutya 12-in-1-Out DC AFCI Combiner Box?

The company evaluated three options: continuing with inverter-level AFCI only, adding external AFCI modules, or switching to an integrated DC AFCI combiner box. The external modules met UL 1699B requirements but added over $2,000 per combiner and lengthened installation by several hours per unit. The integrated Soutya box combined 12 string inputs, per-string arc fault detection, overcurrent protection, and a surge protective device in one enclosure. It was listed to UL 1699B and designed to handle 600 VDC and 1200 VDC system voltages, which matched the company's standard project specifications.

The decision came down to installation economics and system reliability. With the Soutya box, the crew only needed to mount the unit, connect the string leads, and set the AFCI threshold parameters. No external modules or additional enclosures were required. The integrated design also reduced the number of termination points, lowering the risk of future arc faults. The field test on a 1.2 MW rooftop project convinced the engineering team that the product would perform under real conditions.

Implementation Process

The pilot project was a 1.2 MW rooftop array on a refrigerated distribution center. The installation took place over two weeks, with 24 Soutya DC AFCI combiner boxes distributed across the roof. Each box combined 12 strings, with one output feed to the central inverter.

Site prep and mounting: Combiner boxes were mounted on pre-installed strut racks near the exterior walls. DC wiring from the arrays was pulled into the glands and terminated on the input terminals.
AFCI configuration: The installer set each channel's arc fault detection threshold using the built-in DIP switches and a voltage meter. The self-test function verified the arc detection circuit on all 12 inputs without triggering a nuisance shutdown.
Coordination with the inverter: The output of each combiner box was connected to the inverter's DC bus. The AFCI trip signal was wired to the inverter's remote stop input, ensuring that the inverter shut down within 0.5 seconds of a fault – more than twice as as the 2-second requirement in UL 1699B.
Commissioning: After energizing, the crew performed a series of manual arc fault simulations using a calibrated arc generator. All 24 boxes detected the arcs and relayed the trip signal correctly.

The only difficult step was integrating the AFCI trip signal with an older inverter model that lacked a dedicated shutdown input. The team solved this by wiring the trip relay to the inverter's DC disconnect switch controller, a modification that took 30 minutes per inverter. This was a one-time engineering change and did not affect the rest of the installation.

Quantifiable Results

After a full year of operation, the pilot system produced measurable improvements compared to the company's previous combiner box designs.

Arc-fault-related downtime dropped 85% – from an average of 12 hours per quarter to less than 2 hours. The elimination of false trips from inverter startup alone saved 8 hours of downtime per quarter.
Two real arc faults were detected and isolated – one caused by a corroded MC4 connector and one by a loose terminal screw. Both events were caught before thermal damage occurred, preventing an estimated $50,000 in potential repair and liability costs.
False trip rate dropped from 5 per year to 1. The single false trip occurred during an unusual utility grid voltage event, and the reset took 10 minutes.
Installation time per combiner box decreased by 40% – from 4 hours to 2.5 hours – because the crew no longer had to install separate AFCI devices and junction boxes.

The client approved the rollout of the same combiner box design on their next three projects, totaling 4 MW of capacity.

Client Testimonial

"The Soutya AFCI combiner box removed a layer of complexity from our designs. It caught an arc fault that the inverter never saw, and the commissioning was effortless. We've standardized on this box for all our commercial installations." — Senior Electrical Engineer

Lessons and Recommendations

Arc fault protection belongs at the combiner level, not at the inverter. Combiner boxes are the highest-risk junction point for series arc faults because of the many terminations in a small enclosure. Implementing detection there provides faster response and better troubleshooting.
Integrated AFCI lowers total system cost. Even though the Soutya box costs 30% more than a standard combiner box, the elimination of external AFCI modules and reduced installation labor yields a net savings of roughly $1,000 per box. For a 1 MW project with 20 boxes, that is $20,000 in savings.
Commissioning and self-test are critical. Verify the AFCI behavior before energizing the array. Also, coordinate trip logic with the inverter to ensure the shutdown is enough to meet UL 1699B and NEC 690.12 requirements.
If revisiting the project, the team would add remote monitoring of AFCI status. That would enable even faster fault localization and prevent technicians from climbing the roof unnecessarily.