Types of electrical switchboards: which is which?
In a factory or a service building there is rarely "one switchboard" — there are several, each with a function and a place in the chain. Telling them apart helps you read a project, ask for the right quote and understand what is being proposed. This guide walks through the most common types of low-voltage switchboards and explains how they combine.
The tree: from the main board to the sub-boards
Everything starts at the QGBT — main low-voltage switchboard, which receives power from the transformer station or the grid and distributes it. Downstream sit the sub-boards, serving specific zones or functions. Then come the boards that control equipment. Think of a tree: the main board is the trunk, the sub-boards are the branches, and the control and automation boards are where the energy turns into work.
The most common types
- Main switchboard (QGBT) — the principal board: main disconnect, incoming and outgoing protections, busbars sized for the building’s total current. The most demanding in current and protections.
- Sub-board — distributes power within a zone (a floor, a hall, a production line). Fed from the main board, it supplies that zone’s circuits and equipment.
- Control board — controls specific equipment: starting and protecting motors, pumps, fans, with local signalling and control. The board "that makes the machine run".
- Lighting board — dedicated to the lighting and socket circuits of a zone; many small-current circuits, clearly labelled.
- Power-factor correction board — capacitor banks that compensate reactive power. Avoids penalties on the energy bill and relieves the internal network. Common in industry with many motors.
- Changeover board (grid / generator / UPS) — switches the supply between the grid, a generator set or a UPS so that critical loads are never left without power.
- Automation and control panel — houses the PLC, variable-speed drives and the control gear of a process. The evolution of the control board for more complex processes — see industrial automation and control panels.
What changes from one type to another
Four things: the current (from tens of amperes in a lighting board to thousands in a main board), the gear (protections, contactors, capacitors, drives — each type has its own), the enclosure (dimensions and ingress protection suited to the location) and the functions (distribute, protect, control, compensate, switch over). That is what drives the price and the sizing — and why a board is quoted from the project’s scheme, not by type.
How they combine in a project
In a typical industrial plant: a main board at the incomer, sub-boards per hall or line, control boards next to the machines, an automation panel for the line, a power-factor correction board beside the main board and a changeover board for the generator. In an office building: main board, floor sub-boards and lighting boards. All are built and tested to the same standard — IEC 61439 — and delivered with a test report and CE marking.
Frequently asked questions
Does a sub-board need the same certification as the main board?
Yes. The IEC 61439 standard applies to every low-voltage assembly, from the main board to the lighting board. Every board should leave the workshop tested, with a test report and CE marking.
What is the difference between a control board and an automation panel?
A control board uses conventional gear — contactors, relays, push-buttons — to start and protect equipment. An automation panel adds a PLC and drives to control more complex processes. They often coexist in the same project.
Can several types share one enclosure?
It is common — for example, a sub-board with the control section for that zone’s machines. It depends on space, separation between functions and safety during maintenance; it is sized case by case.