The purpose of EN standards is to harmonise technical rules and laws within the European market. Existing ISO standards must generally be adopted as EN standards in unaltered form. However, if an IEC standard is adopted as a European standard, its technical part has minor modifications as per EN requirements.
ISO standards are standards developed by the standardisation institute ISO, and IEC standards are developed by the International Electrotechnical Commission (IEC). EN standards are usually ISO or IEC standards that the European Commission has harmonised.
ISO can develop a standard, e.g. the ISO 12100-1:2003 “Safety of machinery”. When the EU Member States approve the safety standard, the European Commission has to publish it. From that moment on, the standard is a harmonised standard, meaning that all EU Member States need to adopt this standard and withdraw any conflicting national standards.
Once an ISO standard is harmonised, it is renamed EN-ISO XXXXX. Similarly, if an IEC standard is harmonised, its title changes to EN IEC XXXXX. When an EU member state translates a harmonised standard, the name of the standard changes to, for example, BS EN ISO XXXXX or BS EN IEC XXXXX.