Electrical resistance heat tracing is widely used for freeze protection and temperature maintenance of pipelines and vessels in industrial facilities. Reliable and safe operation are essential, especially in industrial facilities such as refineries and chemical plants that frequently contain classified areas. Revised Recommended Practice 515 provides a basis for successful application of heat tracing in unclassified, Class I, Division 2 (CID2), and Class I, Division 1 (CID1) areas. This paper provides background and an overview of recommended practice 515 with special emphasis on the revised portions.