The basic functions of LV switchgear

Switchgear: General term covering switching devices and their combination with associated control, measuring, protective and regulating equipment, also assemblies of such devices and equipment with associated interconnections, accessories, enclosures and supporting structures, intended in principle for use in connection with generation, transmission, distribution and conversion of electric energy [IEV 441-11-02].

Low voltage electrical installation rules such as IEC 60364 series and related national standards give:

• rules for design and erection of electrical installation, and
• requirement for selection of electrical equipement including the devices to ensure protection and control of the electrical installation.

These devices are collectively referred to as «switchgear».

The main functions of switchgear are:

• Electrical protection
• Electrical isolation of the electrical installation, circuits or individual equipment
• Local or remote switching

These functions are summarized below in Figure H1.

Fig. H1 – Basic functions of LV switchgear

Electrical protection against	Isolation	Control
Overload currents Short-circuit currents Insulation failure	Isolation clearly indicated by an authorized fail-proof mechanical indicator A gap or interposed insulating barrier between the open contacts, clearly visible	Functional switching Emergency switching Emergency stopping Switching off for mechanical maintenance

In addition to those functions shown in Figure H1, other functions, namely:

• Over-voltage protection
• Under-voltage protection

are provided by specific devices (lightning and various other types of voltage-surge arrester, relays associated with contactors, remotely controlled circuit-breakers, and with combined circuit-breaker/isolators… and so on)