View source for Standards and description of circuit-breakers

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== Standards ==

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Industrial circuit-breakers must comply with IEC 60947-1 and 60947-2 or other equivalent standards.

Domestic-type circuit-breakers must comply with IEC standard 60898, or an equivalent national standard}}

For industrial LV installations the relevant IEC standards are, or are due to be: 
*60947-1: general rules 
*60947-2: part 2: circuit-breakers 
*60947-3: part 3: switches, disconnectors, switch-disconnectors and fuse combination units 
*60947-4: part 4: contactors and motor starters 
*60947-5: part 5: control-circuit devices and switching elements 
*60947-6: part 6: multiple function switching devices 
*60947-7: part 7: ancillary equipment
*60947-8: Part 8: Control units for built-in thermal protection (PTC) for rotating electrical machines.

For domestic and similar LV installations, the appropriate standard is IEC 60898, or an equivalent national standard.

== Description  ==

{{FigureRef|H21}} shows schematically the main parts of a LV circuit-breaker and its four essential functions: 
*The circuit-breaking components, comprising the fixed and moving contacts and the arc-dividing chamber 
*The latching mechanism which becomes unlatched by the tripping device on detection of abnormal current conditions

This mechanism is also linked to the operation handle of the breaker. 

*A trip-mechanism actuating device:
**Either: a thermal-magnetic device, in which a thermally-operated bi-metal strip detects an overload condition, while an electromagnetic striker pin operates at current levels reached in short-circuit conditions, or 
**An electronic relay operated from current transformers, one of which is installed on each phase
*A space allocated to the several types of terminal currently used for the main power circuit conductors

{{FigImage|DB422405_EN|svg|H21|Main parts of a circuit-breaker}}

Domestic circuit-breakers (see {{FigRef|H22}}) complying with IEC 60898 and similar national standards perform the basic functions of: 
*Isolation 
*Protection against overcurrent

{{FigImage|PB116761|jpg|H22|Domestic-type circuit-breaker providing overcurrent protection and circuit isolation features}}

Some models can be adapted to provide sensitive detection (30 mA) of earth-leakage current with CB tripping, by the addition of a modular block, while other models (RCBOs, complying with IEC 61009 and CBRs complying with IEC 60947-2 Annex B) have this residual current feature incorporated as shown in {{FigureRef|H23}}. 

{{FigImage|PB116762|jpg|H23|Domestic-type circuit breaker with incorporated protection against electric shocks}}

Apart from the above-mentioned functions further features can be associated with the basic circuit-breaker by means of additional modules, as shown in {{FigureRef|H24}}; notably remote control and indication (on-off-fault). 

{{FigImage|DB422406_EN|svg|H24|“Acti 9” system of LV modular switchgear components}}

Moulded-case circuit-breakers complying with IEC 60947-2 are available from 100 to 630 A and provide a similar range of auxiliary functions to those described above (see {{FigureRef|H25}}). 

{{FigImage|PB105112-z|jpg|H25|Example of a Compact NSX industrial type of circuit-breaker capable of numerous auxiliary functions}}

Air circuit-breakers of large current ratings, complying with IEC 60947-2, are generally used in the main switch board and provide protector for currents from 630 A to 6300 A, typically.(see {{FigureRef|H26}}).

In addition to the protection functions, the Micrologic unit provides optimized functions such as measurement (including power quality functions), diagnosis, communication, control and monitoring. 

{{Gallery|H26|Example of air circuit-breakers. Masterpact provides many control features in its “Micrologic” tripping unit||
|PB116184-50.jpg||
|PB116047_20.jpg||
}}