Forms of segregation in Electrical Panels

One of the major aspects that we come across while reading specifications related to electrical panels or distribution boards is the form of segregation. The form of segregation of an enclosure gives information on how the busbars, functional units, and terminals are segregated from each other.

Why Forms of Segregation?

The major reason for separating an assembly is to provide safe access to a part of the assembly while other parts may remain electrically live and in service. Generally, segregation does not add to the electrical performance of the assembly but it provides:

  • Protection against contact with the live electrical parts belonging to the assembly.
  • Protection against the movement of solid foreign bodies from one part of an assembly to an adjacent part.

Basic Terminologies and Symbols used

Busbar:

An electrical busbar is defined as a conductor or a set of conductors that are used for collecting electrical power from the incoming feeders and for distributing it to the outgoing feeders. In other words, it is an electrical junction point where all the incoming and outgoing electrical current in the assembly meets. The busbar system includes the main busbars as well as all the associated distribution busbars.

Functional Units:

A functional unit is defined as a part of an assembly consisting of all the electromechanical elements including switching devices that help to achieve the same function. Some examples of functional units are incomer Feeders, distribution outgoers, individual motor starters, etc.

Terminals:

Terminals are defined as a part of the assembly that facilitate the connection between incoming and outgoing cables and the busbar.

Classification of Forms of Segregation:

Following are the different Forms of Segregation based on IEC 61439 – 1 & 2 standards.

Form separation in switchboards

Form 1

 No Internal Partitions.

Form 1 separation electrical panel

Form 2

Functional units are segregated from the Busbars.

Form 2a

Busbars not segregated from Terminals of External Conductors

Form 2b Separation in electrical panel

Form 2b

Busbars are segregated from Terminals of External Conductors

Form 3

Functional units are segregated from the Busbars.
+
Individual Functional Units are segregated from each another.
+
Segregation of Terminals for External Conductors and the External Conductors from the Functional Units, but not from the Terminals of other Functional Units.

Form 3a in electrical panel

Form 3a

Busbars are not segregated from Terminals

Form 3b in electrical panel

Form 3b

Busbars are segregated from Terminals and External Conductors

Form 4

Functional units are segregated from the Busbars.
+
Individual functional units are segregated from each another.
+
Segregation of Terminals for External Conductors associated with a Functional Unit from the terminals of any other Functional Unit and the Busbars.
+
Segregation of Busbars from the External Conductors.
+
Segregation of the External Conductors associated with a Functional Unit from other Functional Units and their Terminals
+
External conductors need not be segregated from each other

Form 4a in electrical panel

Form 4a

Functional Unit and associated Terminals are in same compartment

Form 4b in electrical panel

Form 4b

Functional Unit and associated Terminals are not in same compartment

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