ACDB and DCDB are distribution and protection assemblies used on different sides of a photovoltaic system. Their contents are not universal: the correct arrangement follows the approved system design, equipment documentation and applicable electrical requirements.
What is a DCDB?
A direct-current distribution box is installed on the PV DC side, between solar strings or arrays and the inverter, depending on the system design. It provides an organized enclosure for the specified DC switching, combining and protective functions.
The required number of string inputs, outputs and protective devices depends on the array and inverter configuration. Components used on the DC side must be explicitly suitable for the specified DC duty; AC ratings should not be treated as interchangeable.
What is an ACDB?
An alternating-current distribution box is used on the inverter output side. It houses the switching and protective devices specified between the inverter and the connected AC distribution system.
The arrangement depends on inverter output, phase configuration, downstream connection and the approved single-line diagram. The enclosure and internal layout should also provide suitable cable entry, identification and safe access for installation and maintenance.
Why the boxes should not be selected by project size alone
A request such as ‘ACDB/DCDB for a 10 kW system’ may not contain enough information for a reliable quotation. Two projects with the same nominal capacity can use different module strings, inverter arrangements, cable routes, protection philosophies and site conditions.
The supplier needs the design details that determine the enclosure and component schedule. When available, share the approved single-line diagram and bill of materials rather than asking the supplier to infer the design.
Information to provide for a DCDB quotation
Use the approved design to prepare the request. Typical information includes:
- System DC voltage and design current information
- Number of string inputs and outputs
- Specified isolating, overcurrent and surge-protection devices
- Cable sizes, connector or gland requirements and entry direction
- Enclosure material, mounting location and environmental requirement
- Monitoring or indication requirements, if any
Information to provide for an ACDB quotation
For the AC side, share the details relevant to the inverter output and downstream distribution:
- Single-phase or three-phase arrangement
- Number and rating of inverter inputs to the board
- Specified incomer, outgoing and protective-device schedule
- Cable sizes, gland requirements and termination details
- Enclosure material, mounting location and environmental requirement
- Metering, indication or monitoring requirements, if specified
Inspect the complete assembly, not only the enclosure
When comparing quotations, review the exact bill of materials, component makes and models, enclosure specification, wiring arrangement, terminals, glands, labels and documentation. A similar-looking box can contain a substantially different assembly.
Final device selection, coordination, installation and testing must be handled by qualified professionals in accordance with the approved design and applicable requirements.
Key takeaway
A DCDB serves the solar DC side; an ACDB serves the inverter’s AC output side. For a useful quotation, provide the approved electrical design, circuit counts, device schedule, cable details and enclosure requirements instead of project capacity alone.
