Electricity + Control May 2019

DRIVES, MOTORS + SWITCHGEAR

Understanding the terminology in IEC 61439

Johan Basson, Managing Director, JB Switchgear Solutions (Pty) Ltd

I n this tutorial we look at the topic of ‘Internal forms of separation’ in electrical switchgear and controlgear assemblies, where a variety of standard arrangements are detailed. They are la- belled Form 1, Form 2, Form 3 and Form 4. Forms 2, 3 and 4 are further broken down into Forms 2a, 2b, 3a, 3b, 4a and 4b. Each form relates to the internal separation of busbars, functional units and terminals. Internal separation is achieved by the use of barriers or partitions (including metallic or non-metallic), insu- lation of live parts, or an integral housing (such as a moulded case circuit breaker). The internal bar- riers should provide protection against contact to IPXXB and/or IP2X standards. Form 1 has no separation, while Form 4b has the greatest, with busbars, functional units and terminals all being separated – as shown in the figures below. The main reason for separating an assembly is to facilitate access to a part of the as- sembly while other parts may remain energised and in service. Although in general separation does not improve the electrical performance of the assembly it does provide: - Protection against contact with live parts be- longing to the adjacent functional units The IEC 61439 series of standards is applicable to low voltage switchgear and controlgear assemblies. Johan Basson looks at some of the terminologies and explains them so that the reader may gain better understanding of their meaning. Extracts from the standard itself are used extensively.

- Protection against the passage of solid foreign bodies from one unit of an assembly to an ad- jacent unit.

1. The different forms of internal separation for electrical switchgear and controlgear assemblies facilitate access to a part of the assembly while other parts may remain energised and in service. Take Note! 1

Forms of internal separation

Busbars, including distribution busbars

Enclosure

Internal separation

Functional unit

Terminal(s) for external conductors

Form 1 • No internal separation

Form 2 • Separation of busbars from all functional units

Form 2a: Terminals not separated from busbars

Form 2b: Terminals separated from busbars

8 Electricity + Control

MAY 2019