A mid-sized solar EPC company operating in the commercial and industrial sector faced a recurring problem: integrating DC power from photovoltaic arrays with AC power from the grid or battery inverters required separate combiner boxes, increasing labor, wiring, and enclosure costs. The solution came in a single enclosure that handles both DC and AC inputs—the singielectric YB4-1-1 DC+AC Combiner Box, rated for 600V and 1000V systems.
The company, with over 50 MW installed annually, professional in rooftop and ground-mount systems paired with battery storage. Each project required a DC combiner box for the PV strings and a separate AC combiner box for the inverter output. This dual-box approach consumed valuable wall space, doubled wiring runs, and complicated commissioning. On a recent 2 MW project, the installation team spent an extra 40 hours coordinating the two boxes, and material costs exceeded the budget by $3,200.
After assessing alternatives—including using larger separate boxes or custom-built switchboards—the engineering team chosen the singielectric YB4-1-1 because it combined both functions in one NEMA 4X enclosure. The key decision factors were the 600V/1000V dual rating, a compact 1-in-1-out configuration, and built-in surge protection for both DC and AC circuits. The product also complied with UL 1699B for DC arc-fault protection and IEC 62606 for AC arc-fault detection, eliminating the need for external arc-fault devices.
The project was a 1.5 MW commercial rooftop with 500 kW of battery storage. The YB4-1-1 units were installed at each inverter cluster—one per 250 kW block. Each unit accepted three DC strings (fused at 15A) and one AC input from the inverter. The installation involved:
One challenge was coordinating the DC and AC disconnects to meet local code requirements. The YB4-1-1 included a lockable handle that simultaneously isolates both sources, simplifying the approval process.
| Metric | Before (separate boxes) | After (YB4-1-1) | Improvement |
|---|---|---|---|
| Installation labor per unit | 8 hours | 3.5 hours | 56% reduction |
| Enclosure & wiring cost per MW | $4,800 | $2,100 | 56% reduction |
| Commissioning time per site | 12 hours | 5 hours | 58% reduction |
| Arc-fault false trips (annual) | 3–5 | 0 | Eliminated |
The overall project schedule shortened by 8 days, and the customer saved $6,700 in total installation costs. The single-box design also freed up wall space for future expansion.
| Feature | Specification | Benefit |
|---|---|---|
| Dual volt-level rating | 600V DC / 1000V DC & 600V AC | Compatible with most commercial PV and battery systems |
| Integrated DC AFCI | UL 1699B compliant | Detects series and parallel arcs without external device |
| Integrated AC AFDD | IEC 62606 compliant | Protects against AC arc faults |
| Surge protection | Type 2 SPD for DC and AC | Handles lightning-induced surges up to 40 kA |
| One-box design | NEMA 4X, lockable handle | Reduces installation labor and meets code |
No. The YB4-1-1 is rated for a maximum-val of 1000V DC and 600V AC. For 1500V systems, use the singielectric YB4-1-1-HV model.
Each DC input is fused at 15A; the AC input can handle up to 30A. The total combined output is limited to 60A.
No. The built-in DC AFCI and AC AFDD meet the requirements of UL 1699B and IEC 62606, so no additional arc-fault protection is needed.
Yes. The NEMA 4X enclosure is weatherproof and UV-resistant, suitable for direct sunlight and rain.
The singielectric YB4-1-1 DC+AC Combiner Box offers a practical solution for solar installers seeking to cut costs and complexity. By merging DC and AC protection in one enclosure, it reduces labor, material, and commissioning time while maintaining compliance with key safety standards. For EPCs working on combined systems, this product can translate to lower project costs and faster turnarounds.
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