Different Forms of Segregation for Switchboards

Switchboards form the heart of the distribution systems in Industry. The safety and reliability of any industry depends on Switchboard design. As the type of applications in industry vary so do the design aspects for switchboards. One of the aspect often misunderstood is form of segregation or form of separation in Panels. The form of a panel needs to be carefully specified as a balance needs to be strike between Cost and Safety. Let us check the various forms of separation as specified in IEC 60439.

1)      Form 1 Panel - This is the most basic form of panel. There is no segregation between functional units (Switchgear) and busbars. The degree of protection of such panels is typically IP20. This form of panels is typically found in small homes or shops.
2)      Form 2a and 2b – In case of form 2 panels, there shall be separation between busbars and switchgear. However, form 2a or 2b will depend whether segregation has been made between busbar and switchgear terminals. In case the terminals and busbar lie in the same enclosure, the panel is form 2a . This is typically observed with double door distribution boards for homes and offices . In case of form 2b, busbar and terminals are segregated from each other. This is the case for non- compartmentalised panels. In both cases, degree of protection shall be IP 42/43 .

3)      Form 3a and 3b – In case of form 3 panels, the functional units are separated from each other by means of compartments. The segregation between bus bar and terminals will be identical as in case of 2a and 2b. Form 3b is the most prevalent type of panels used in the industries. The typical degree of protection for such a panel will be IP 54.

4)      Form 4a and 4b – For form 4 Panels, the outgoing terminals of each functional unit are isolated from each other in case of form 4a and from the busbars in case of 4b. This is the most advanced and complex form of panel which can provide extremely high safety as well as reliability. However, such a construction entails very high costs and is only used in critical installations like data centres.

Please note that form 3 and form 4 panels provide good safety against direct contact with live parts and bus bars. However, certain conditions like internal arc will persist. Thus, the system designer should keep these things in mind. Only after complete system and process analysis should form of panel be decided.
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