Provided that the item is within the scope of the EPS Regulations then all 'equipment', 'protective systems', 'devices' and 'components' placed on the EU market or put into service from 1 July 2003 is required to be conformity assessed in compliance with these Regulations. US manufacturers can themselves follow the appropriate conformity-assessment procedure, involving a notified body as necessary, and attach the CE mark to their products. This would be the appropriate course of action for US products which are manufactured in quantity and used widely in the EU. An end user who imports equipment from outside the EU, which has not been through the EPS Regulations conformity-assessment procedure, has the duty to ensure it complies with the EPS Regulations, and to hold the Declaration of Conformity and related documentation.
Norway is inside the EEA (European Economic Area) and as such is treated, for the purposes of EU Directives, in exactly the same way as an EU member state. This means that equipment manufactured in Norway for supply within the EU, should be conformity assessed to the ATEX Directive's essential health and safety requirements (EHSRs), and CE marked in line with the Norwegian equivalent of the EPS Regulations.
If the assembly is intended to be used in a hazardous area, all the parts should conform to European requirements. It may be possible to arrange for an ATEX notified body to re-certify the American certified parts. This will be simpler if all the technical documentation is available from the original manufacturer. However, even if the product can be shown to be compliant to the ATEX essential health and safety requirements, it will still be necessary to arrange for the appropriate product quality assurances checks to be made. Further, all the documentation should be kept in Europe by the importer or end user, so it is available for inspection by the national authorities responsible for ATEX (in the UK, HSE).