Because of the wide variety of pool and spa sizes and configurations, the OG-400 program certifies families of system designs. This means that the certification addresses a general configuration of collectors, type (direct or indirect), pool/spa tie-in, and components. There may be variations within the size of the system within a given certification. But, all of the systems covered in a certification must share the same layout, components and placement, pool tie-in and collectors. Where variations to the design are permitted, the certificate will specifically note them, so that code officials can easily confirm whether the system they are inspecting matches the certification.