Low Voltage Switchgear

A distribution board normally refers to the final circuit level, with miniature or moulded case breakers feeding sub-circuits in a building. Low voltage switchgear refers to the main distribution level, with an air circuit breaker incomer, instrument transformers, metering and outgoing feeders. The boundary is conventional rather than technical, and the two terms overlap in practice — what matters is the fault level, the form of separation and the verified rating, not the label on the drawing.

IEC 61439 defines low voltage as up to 1000 V AC. In practice, industrial LV distribution is built for 400 V, 415 V, 440 V or 690 V at 50 or 60 Hz. A 690 V board is not a 400 V board with a different label: device voltage ratings, clearances and the routine dielectric test voltage all change, so 690 V devices must be specified throughout, including contactors and relays.

Form 2b for general distribution where shutdowns are possible, Form 3b for motor control centres, and Form 4a or 4b where individual functional units must be maintained while the busbar stays live. Each step up increases enclosure depth and cost, so the right choice is the one that matches the plant's actual maintenance policy rather than the highest form available.

Size it from the prospective fault current at the board terminals and the maximum demand current, then check the temperature rise at the real ambient inside the enclosure. A busbar rated 2500 A at 35 °C may carry only around 2200 A at 45 °C, and the short-time withstand must exceed the transformer's fault contribution for the duration the upstream protection takes to clear.

Yes. Send the original drawings or accurate measurements, the busbar position and rating, the device makes already in use and the paint reference. Matching the existing protection philosophy and device family matters as much as matching the dimensions, because mixed makes complicate both discrimination and spares.

Air circuit breakers are used for main incomers roughly above 1600 A, with adjustable protection and draw-out construction for maintenance. Moulded case breakers cover the middle range and are commonly motorised for remote operation. Miniature breakers are final-circuit devices and are not used as incomers on distribution boards of significant rating.

GA drawing, single-line and wiring diagrams, device datasheets, the verified ratings table, the design verification reference, the routine test report for that serial number, and the operation and maintenance manual. Site commissioning support and witnessed factory acceptance testing can be arranged on request.

Custom LV assemblies are quoted per project rather than per unit, so both MOQ and lead time depend on the configuration, the device make and the documentation scope. Send the single-line diagram, fault level and load schedule and we will confirm quantity, price and delivery in the technical proposal, usually within one working day.