Circuit Protection Devices

Too much current flowing through an electric circuit can damage the circuit and can create a safety hazard. How much current is "too much current"? That depends on the circuit and its components. For some circuits, 1 ampere would be too much current, while for other circuits 1 ampere would be perfectly acceptable. Circuit protection devices protect electrical equipment by rapidly disconnecting power to components in the event of an abnormal overload conditions resulting from excessive voltages, ground faults, and accidental shorting of a circuit. Two types of circuit protection devices are common; fuses and circuit breakers both operate by opening and interrupting current to the circuit. A fuse or circuit breaker is designed to create an open circuit if too much current flows through it. You can think of it as a switch that automatically turns itself off if the current through it exceeds a certain level. When a fuse is "blown" by having too much current pass through it, the fuse is ruined and must be replaced. On the other hand, when a circuit breaker is "tripped" by excessive current, the circuit breaker can be reset and used again, instead of being discarded. The choice of which to use depends on the specific application, circuit type, its electrical specifications, space available, environmental constraints, and customer preference. In the US, the National Electric Code (NEC) exists to guide electricians in the proper installation of electrical equipment and defines the specific requirements for circuit protection. In Canada the Canadian Electric Code (CEC) exists to provide similar guidance. Other areas of the world have equivalent country or local codes. A proper circuit protection strategy reduces long-term maintenance needs and other costs, and minimizes system downtime. This 3-hr Quick Book provides an overview of circuit protection devices and is based entirely on Naval Education and Training Materials (NAVEDTRA 14175), Electricity and Electronic Training Series; Module-3 and covers Chapter 2 titled "Circuit Protection Devices." This course is aimed at students, professional engineers, service technicians, energy auditors, operational & maintenance personnel, facility engineers and general audience. At the conclusion of this course, the reader will be able to: - State the reasons why circuit protection is needed. - Define a direct short, an excessive current condition, and an excessive heat condition. - State the way in which circuit protection devices are connected in a circuit. - Identify two types of circuit protection devices and learn their types and characteristics. - List the three time delay ratings of circuit breakers. - Define selective tripping and state why it is used. - Identify the factors used in selecting circuit breakers. - List the methods of checking and the items to check when replacing and/or maintaining fuses and circuit breakers.