BS EN Low-voltage switchgear and controlgear. Amends and replaces BS EN which remains current. BS EN applies to circuit-breakers, the main contacts of which are intended to be connected to circuits, the rated voltage of which does not exceed 1 V a. It applies whatever the rated currents, the method of construction or the proposed applications of the circuit-breakers may be. The requirements for circuit-breakers which are also intended to provide earth-leakage protection are contained in Annex B.
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They are both standards that specify requirements for low-voltage circuit breakers. Is there more in common? Which one if for homes, which one for industry? IEC , which I introduced at length in the first of these blog posts , governs CBs for industrial applications. They protect electrical power distribution of up to volts a. As for IEC , it relates to the a. The standard states that the top rated current is A, while the lowest is 6A and maximum value of rated short-circuit capacity Icn is 25kA.
Just those basic tech specs tell us how different the use of circuit breakers defined by our two standards are. The rated voltage currently required in industrial-use CBs is , volts or higher. Compare those numbers to the V upper limit between phases for residential MCBs. The same goes for impulse withstand voltage Uimp. IEC requires 4kV, in line with the use for final circuits. Whereas for industrial circuit-breakers, usual values of Uimp is 6 or 8kV, in line with the position of the circuit-breaker, at the origin of the installation.
Comparison table of characteristics of miniature circuit breakers MCBs usually used in the IEC market Who confuses the two standards and how?
Procurement managers in utilities, too, can get things wrong. But happen it does. The history of standard IEC may have something to do with it. The concept behind it as it evolved in ss was a single standard for all low-voltage switchgear. That notion, combined with lack of knowledge or technical expertise, may have led to the misconception that there is one standard for all CBs. Consequences can be dire if residential CBs are used instead of industrial ones.
An MCB designed for indoor, pollution-free conditions would be woefully inadequate for harsh, outdoor applications that require pollution degree 3. This is the reason why manufacturers in addition provide a wide scope of different curves: K, Z, MA.
Typically IEC certified CBs meet minimally required performance to proof proper protection of household installations: Pollution degree 2, impulse voltage 4kV, isolation voltage is the same as nominal voltage V. That is the reason why usually we meet limited number of printed technical information on CBs.
These CBs are intended for use of indoor, pollution and humidity-free conditions: household or similar installations overcurrent protection by uninstructed people and not being maintained. In other words — in final distribution electrical switchboards of buildings which nominal current does not exceed A. Usually these circuit breakers sold by electrical retailers: simple to install, safe and easy to use even after many years without maintenance.
Example of Acti9 circuit breaker used for buildings and industry applications The most suitable solution for use are MCBs certified with both standards as their performance meets requirements of use for residential installations and high enough for use in industry and infrastructure applications.
Due to high level of protection performances these CBs should be used at least in incoming electrical switchboards of buildings applications. The best way to avert them is tightly worded, highly enforced national regulations. And for prescribers to specify what CBs will be used for and then to check the standard for that use.
Have you ever mixed up the two standards? Leave us your comments below!
BS EN 60947-2:2017
IEC 60898-1 and IEC 60947-2: a tale of two standards