When does a rooftop solar plant need a direct current distribution box, and which circuit breaker type does the specification use on that side?
The Ministry of New and Renewable Energy (MNRE) specification says a direct current (DC) distribution box may not be required for small plants if the inverter has a suitable arrangement. Where fitted, miniature circuit breakers (MCB) are used up to 63 amperes and moulded case circuit breakers (MCCB) above 63 amperes.
DC distribution box, section 6
These are clauses from the technical specification in Annexure 3 of MNRE's guidelines for its residential rooftop solar scheme, Pradhan Mantri Surya Ghar: Muft Bijli Yojana. A factory is not bound by them, but they are a published checklist to hold a quotation against.
- It may not be required for small plants, if suitable arrangement is available in the inverter.
- Where fitted it receives the DC output from the array field and is dust and vermin proof with ingress protection (IP) of 65 or better, as per site conditions.
- Bus bars are made of "EC grade" copper of required size; the specification prints the term without defining it.
- Suitable capacity MCB or MCCB control the DC power output to the inverter, with necessary surge arrestors. MCB shall be used for currents up to 63 amperes, and MCCB for currents greater than 63 amperes.
Alternating current (AC) distribution box, section 7
- Controls the AC power from the inverter, with surge arrestors if required, and connects to the mains at the low tension bus bar while in grid-tied mode.
- All switches, circuit breakers and connectors conform to International Electrotechnical Commission (IEC) 60947 or Indian Standard (IS) 60947, Parts I, II and III.
- Panels are metal clad, totally enclosed, rigid, floor mounted, air-insulated, cubicle type for 1 or 3 phase, 415 or 230 volts, 50 hertz, or voltage levels as per Central Electricity Authority and state regulations.
- Designed for a minimum expected ambient temperature of 45 degrees Celsius, 80 percent humidity and dusty weather. Indoor panels IP 54 or better and outdoor panels IP 65 or better.
- A residual current breaker shall be used if the inverter does not have the required earth fault or residual current protection.
Array junction boxes, section 5
- Made of glass reinforced plastic, fibre reinforced plastic, powder coated aluminium or cast aluminium alloy, with a full dust, water and vermin proof arrangement.
- Copper bus bars or terminal blocks in a box conforming to IP 65 or better and IEC 62208, with a hinged door and ethylene propylene diene monomer (EPDM) rubber gasket.
- Mounted on the structure so they are easily accessible and protected from direct sunlight and harsh weather.
What to read on the single line diagram
For a plant of tens of kilowatts, check that the DC side has a breaker rating that matches the string current, that the breaker type follows the 63 ampere line, and that surge arrestors are fitted where the design needs them on the DC and AC sides (the specification says necessary on DC and if required on AC). For a small plant with no DC box, ask the vendor to show where the DC isolation is inside the inverter.
What Senseible does here
Senseible reads fuel invoices and electricity bills into monthly records. It does not review electrical drawings or protection settings.
Last reviewed 2026-11-06. Re-check clause numbers and figures against the current version of the guidelines before you rely on them. Clauses are in Annexure 3, sections 5 to 7. Electrical design is for a qualified engineer to approve.