What Is Form of Separation? A Guide to Form 1, 2, 3 and 4 Internal Separation in Low-Voltage Panels
In low-voltage panels, safety and service continuity depend not only on the equipment used, but also on how the sections inside the panel are separated from one another. The “form of separation” (internal separation) defined in IEC 61439-2 specifies the degree to which busbars, functional units and terminals for external conductors are physically separated. Choosing the right form directly affects personnel safety during maintenance, energy continuity in the event of a fault, and ease of intervention.
Why does internal separation matter?
Internal separation limits the extent to which a fault in one compartment — or maintenance work carried out there — affects neighbouring compartments. This reduces the risk of accidental contact with live parts and makes it possible to work on a specific section without de-energising the entire installation. In critical facilities, this means shorter downtime and improved occupational safety.
Forms of separation
Form 1 – No separation: Busbars, functional units and terminals are located in a single volume, with no internal barriers or partitions.
Form 2 – Separation of busbars: Busbars are separated from functional units. In Form 2a the terminals for external conductors are not separated from the busbars, whereas in Form 2b the terminals are also separated from the busbars.
Form 3 – Separation of functional units: Busbars are separated from functional units, and functional units are separated from each other. In Form 3a the terminals are not separated from the busbars; in Form 3b the terminals are separated from the busbars.
Form 4 – Full separation: The highest level of separation; busbars, functional units and terminals are separated from one another. In Form 4a the terminals are in the same compartment as the associated functional unit; in Form 4b the terminals are located in separate compartments.
Which form should you choose?
The form level is determined by the criticality of the facility, the maintenance policy and the need for energy continuity. In data centres, hospitals and large industrial plants, where downtime is costly, Form 3b or Form 4b is usually preferred. For smaller distribution boards, Form 2 is often sufficient. Higher form levels provide greater safety and serviceability, but they also increase the size and cost of the panel. The selection therefore requires striking the right balance between requirements and cost.
The Devpan approach
At Devpan, we design and manufacture our low-voltage panels with the form of separation suited to each project’s requirements, in accordance with IEC 61439-2. Our engineering team analyses the needs of the facility and works with you to determine a safe, sustainable and cost-balanced internal separation solution.
