If you are just installing complete equipment supplied by a manufacturer, you should ensure it is installed correctly by following the manufacturer's installation instructions and specifications. In such cases, the equipment should be supplied to you CE marked with a Declaration of Conformity in the name of the manufacturer (or their authorised representative). You should ensure that any damaged or misplaced safety components are replaced (by the equipment manufacturer), and that the equipment is complete and in safe working order. If the item is lifting equipment, it will need to have a LOLER-specific thorough examination prior to first use, to confirm its safe installation. There are also specific requirements relating to the safe installation of gas appliances.
Where you build up the equipment from parts supplied by a number of manufacturers or make some of the components yourself, you will be classed as the manufacturer of the final product. For example, if you motorise existing manually operated gates, they become a new machine for which you are responsible. You will then need to follow the conformity assessment full requirements of the Machinery Directive, including: