Many projects attempt to save money by omitting small protective components. These small savings can often become significant losses when a system trips, fails, or requires expensive repairs. In a solar plant, ACDB, the Alternating Current Distribution Box, and DCDB, the Direct Current Distribution Box, are low-cost safeguards that protect performance, uptime, and people. Think of them as the spine of your system, steady and essential.
What is DCDB & ACDB? What They Are, Where They Sit?
DCDB sits between the solar panel strings and the inverter. It protects the inverter and each string from faults that originate on the DC side.
ACDB sits between the inverter and the load or grid. It protects the AC side and provides isolation and coordination with downstream protection.
Both boxes are protection and distribution points, not just junction boxes.
What Lives Inside DCDB & ACDB Boxes?
Typical internals, selected to match your design:
- Fuses, MCBs, or MCCBs for overcurrent protection and isolation.
- SPDs, surge protection devices, are used to divert lightning or switching surges safely to earth.
- Isolators or disconnect switches for safe maintenance.
- Connectors, cable glands, busbars, and earthing bars for reliable terminations.
- IP65 enclosure that is dust and water-resistant, usually UV-stable, and flame-retardant.
The ratings of fuses, MCBs, and SPDs must match the string voltage, current, and temperature conditions, as well as the inverter specifications and fault levels. One size never fits all.
DCDB Options & Why They Matter?
Common configurations:
- 1-in 1-out, a single string to a single input.
- 2-in 2-out, independent protection and isolation for each string.
- Combined outputs, such as 3-in-1-out or 4-in-1-out, are used when strings feed a common MPPT through properly rated fusing and busbars.
Benefit of multiple inputs with independent protection: a weak or shaded string can be isolated, so it does not pull down the healthy strings. That means more consistent energy yield.
ACDB Options
Available in single-phase and three-phase variants.
- Placed between the inverter output and the load or grid connection.
- Coordinates protection with downstream breakers and provides an additional layer of protection against short circuits and overloads on the AC side.
How Protection Actually Works?
- Fuses and MCBs interrupt overcurrent and short circuits, protecting cables, strings, and equipment.
- SPDs clamp surges and divert energy to earth, which reduces stress on inverter electronics during lightning or switching events.
- Disconnects provide technicians with a safe way to isolate specific parts of the system for service.
Installation & Build Quality Checklist
- Use IP65, UV-stable enclosures, with proper gaskets and cable glands.
- Bond the earthing correctly, keep the earth leads short and direct.
- Use the right tools to crimp lugs, avoiding loose strands and hot spots.
- Keep DC cable runs neat and as short as practical; avoid sharp bends.
- Leave a clear wiring diagram inside the lid for maintenance teams.
- Consider minor fire resistance in materials and spacing to contain a fault.
Common cost-cutting mistakes that backfire
- Skipping SPDs entirely.
- Using under-rated fuses or DC components on the AC side, or AC parts on the DC side.
- Poor cable glands, which invite moisture and dust.
- Combining strings without proper fusing and busbar sizing.
- Ignoring ambient temperature effects on voltage and current.
These shortcuts increase nuisance trips, damage inverters, and reduce production. The small extra cost of a well-built ACDB and DCDB pays for itself quickly.
Also read: Connecting Solar to the Grid is Harder Than You Think
Simple Selection Guide You Can Apply TODAY
For DCDB
- Note your array Voc at the lowest site temperature and Isc with a safety factor.
- Match fuse type and rating to PV use; gPV fuses are standard.
- Pick SPD type and Ucpv to suit your string voltage and earthing scheme.
- Choose the number of inputs and outputs based on the number of strings per MPPT.
- Select an enclosure that is IP65, UV-stable, and sized for heat dissipation.
For ACDB
- Confirm the voltage and phase, as well as the inverter’s kVA rating.
- Select an MCB or MCCB with the correct breaking capacity and curve.
- Add Type 2 SPD for most rooftop and small ground-mount sites; use Type 1 where lightning exposure or external SPD coordination is required.
- Include an isolator and, if your standards require it, an RCCB or RCBO.
Conclusion
If you want a solar plant that performs silently for years, treat ACDB and DCDB as the backbone. They are inexpensive compared with panels and inverters, yet they guard your production, reduce failures, and make maintenance safe and simple. Do not skip them to cut costs. Specify them correctly, install them carefully, and your system will thank you with stable output.
Frequently Asked Questions (FAQs)
If the inverter already has protection, do I still need ACDB or DCDB?
Yes. External boxes improve selectivity, isolation, and serviceability. They also protect cabling and terminations that the inverter does not cover.
Where should I mount them?
Mount the DCDB close to the inverter or at the string combiner location, keep DC runs short, shaded, and accessible. Mount the ACDB near the inverter output or main AC point, with clear working space.
What enclosure rating is sufficient for outdoor use?
IP65 with UV-stable construction is a practical baseline for Indian conditions. Use sunshades or ventilated covers where direct sunlight is severe.