2-1
CHAPTER 2
CIRCUIT PROTECTION DEVICES
LEARNING OBJECTIVES
Upon completion of this chapter you will be able to:
1. State the reasons circuit protection is needed and three conditions requiring circuit protection.
2. Define a direct short, an excessive current condition, and an excessive heat condition.
3. State the way in which circuit protection devices are connected in a circuit.
4. Identify two types of circuit protection devices and label the schematic symbols for each type.
5. Identify a plug-type and a cartridge-type fuse (open and not open) from illustrations.
6. List the three characteristics by which fuses are rated and state the meaning of each rating.
Identify a plug-type and a cartridge-type fuse (open and not open) from illustrations.
7. List the three categories of time delay rating for fuses and state a use for each type of time-delay
rated fuse.
8. List the three categories of time delay rating for fuses and state a use for each type of time-delay
rated fuse. Identify fuses as to voltage, current, and time delay ratings using fuses marked with
the old military, new military, old commercial, and new commercial systems. List the three
categories of time delay rating for fuses and state a use for each type of time-delay rated fuse.
9. Identify a clip-type and a post-type fuse holder from illustrations and identify the connections
used on a post-type fuse holder for power source and load connections.
10. List the methods of checking for an open fuse, the items to check when replacing a fuse, the
safety precautions to be observed when checking and replacing fuses, and the conditions to be
checked for when conducting preventive maintenance on fuses.
11. Select a proper replacement and substitute fuse from a listing of fuses.
12. List the five main components of a circuit breaker and the three types of circuit breaker trip
elements.
13. Describe the way in which each type of trip element reacts to excessive current.
14. Define the circuit breaker terms trip-free and nontrip-free and state one example for the use of
each of these types of circuit breakers.
15. List the three time delay ratings of circuit breakers.
16. Define selective tripping, state why it is used, and state the way in which the time delay ratings
of circuit breakers are used to design a selective tripping system.
17. Identify the factors used in selecting circuit breakers.
