Publisher Summary The manufacturer of electrical apparatus may produce and certify it to comply with a given standard. Once in the hands of a user, the manufacturer has no control over the safety aspects of the way in which it is selected, installed, commissioned, inspected, and maintained. Therefore, the manufacturer cannot be held responsible for the consequences. The responsibility is placed on the owner of a plant, perhaps delegated to the user of the installation to ensure that it begins and remains as a safe installation. Hence, there are separate requirements for the manufacturer and for the user of any explosion-protected apparatus. The current version of the standard does not always recognize the different approaches in place, but it is the first attempt to harmonize the installation in hazardous areas using an international platform in order to ease the difficulty of installing a piece of equipment certified in a different country. The wider practical interpretation of the IEC and other codes that are still in place in many countries are discussed. The chapter also explains the selection according to temperature classification and apparatus grouping.