In this EC&M Tech Talk Randy Barnett discusses in five different sections the concepts and rules of overcurrent protection. Overcurrent protective devices include the fuses and circuit breakers installed to open circuits in the event of a short circuit or ground fault. Operation of electrical equipment above its rating is an overload. Overload devices are used to open circuits should excessive current flow in a circuit for a certain amount of time.
This Tech Talk begins with the basics of overcurrent and a simple example of how increasing current in a circuit can rapidly produce excessive heat. Overloads, how they operate to open the circuit and typical setting requirements are given. Next, in the third section, fuse operation and ratings are discussed. Circuit breakers are covered in section 4. Finally, important points from Part I of Article 240 Overcurrent Protection are discussed.
Key topics from Article 240 include provisions for sizing overcurrent protection and when to choose the next higher rated overcurrent device when sizing calculations do not provide for a standard device rating. Understanding the basics of overcurrent protection helps safeguard an installation against one of the most severe electrical hazards – fire!
About the Author
Randy Barnett
CESCP
Randy Barnett is an NFPA Certified Electrical Safety Professional, a long-time journeyman electrician, instructor and author with expertise in industrial electrical construction and maintenance. He is Electrical Codes & Safety Manager for NTT Training. Because of his ability to develop and deliver quality programs, Randy has trained more than 10,000 students in all 50 states, including Canada, Singapore, Afghanistan, Dubai, Trinidad, and Saudi Arabi. His articles appear in numerous trade publications and, his book on "Commercial and Industrial Wiring" is used as an entry-level text in many electrician training programs. Randy also appears at various corporate and trade association speaking engagements and consults on training program design and implementation. Randy is a graduate of the U.S. Navy Nuclear Power School, served as a nuclear electrician in submarines and holds a B.S. in business.