Main distribution board (MDB) 0.4 kV

A main distribution board (MDB, ГРЩ) is the main low-voltage assembly of a facility. The board receives a 0.4 kV supply (380/220 V, 50 Hz) from a transformer substation or a supply network, meters it and distributes electricity along the outgoing lines, to distribution points and workshop boards, and protects the lines against overloads and short-circuit currents. Networks with a solidly earthed or isolated neutral — TN-C, TN-C-S, TN-S, IT.

The board is installed in an electrical switchroom, cable entry and exit are provided from below, and access is single-sided (front). It is used at industrial facilities, in business centres, residential, municipal and public buildings.

A typical MDB comprises an incoming cabinet, a metering cabinet, a bus-section circuit breaker or disconnector, an ATS section, groups of outgoing devices on busbars and, where required, a reactive power compensation cabinet. The switching apparatus is of the air-break and moulded-case type: air circuit breakers (ACB) on the incomers and the bus-section, moulded-case circuit breakers (MCCB) on the outgoing lines, plus switch-disconnectors, PN-2/PPN fuses and current transformers for the metering unit. The specific composition and ratings are selected for the project from the single-line diagram.

How the MDB differs from neighbouring designs. A VRP (incoming distribution switchboard) sits at the point where the supply cable enters a building; the MDB is the main assembly of the facility, feeding the distribution points and workshop boards, so at a small facility these roles coincide. RUNN is the switchgear on the 0.4 kV side of a power transformer: it works inside a package substation or outdoors on a pole-mounted one, while the MDB is fed from it and stands in the switchroom. The MDB contains no power transformer and no high-voltage compartment — it is not a package transformer substation.

Technical characteristics

LK Energy Group is a Ukrainian manufacturer of switchgear equipment from Odesa: company since 2005, own factory since 2015. The boards are manufactured at our own production facility to our own technical specifications and undergo inspection by the quality control department and the electrical testing laboratory.

Approximate price of an MDB, VAT included: 250 A, two incoming feeders — from UAH 100,000; ATS section — on request. The exact cost is determined from the single-line diagram. Prices as of 09.2026.

Send us your single-line diagram or a completed questionnaire and we will prepare a technical proposal with ratings, layout and lead time.

A main distribution board (MDB), also called the main switchboard, is a low-voltage 0.4 kV assembly (380/220 V, 50 Hz) that receives the entire incoming supply of a facility, meters it and distributes it to the outgoing lines, distribution points and workshop boards, protecting them against overloads and short-circuit currents. A typical MDB comprises two incoming feeders, a bus-section device with an ATS section, a metering unit and outgoing device groups. An MDB differs from a VRP by role rather than equipment class: the VRP sits where the supply cable enters a building, whereas the MDB is the facility’s main assembly; at a small facility one assembly does both. It differs from RUNN switchgear by its point of supply: RUNN sits on the 0.4 kV side of a power transformer, inside a package substation or outdoors on a pole-mounted one, while the MDB is usually fed from it and stands in the switchroom. There is no power transformer inside — this is not a package substation. Ratings, circuit and layout are project-specific.

Structurally, the MDB is built from our RUNN-E cabinets or ShchO-90 panels. See RUNN cabinets.

The MDB warranty is 2 years (extended to 5 years by agreement); enclosure metalwork — 10 years. Manufacturer — LK Energy Group, switchgear equipment, Odesa: since 2005, own factory since 2015.