2. When is the lightning hazard least?

3. What actions can electricity produce? Which involves the greater hazard to the value of property?

4. When is a piece of apparatus called "self-protecting"?

5. Why must a protector for telephone apparatus work more quickly for a large current than for a small one?

6. State the general problem which heating hazards present with relation to telephone apparatus.

7. What is the most nearly universal electrical hazard?

8. Sketch and describe the saw-tooth lightning arrester.

9. Make diagram of the carbon-block arrester and state its advantages.

10. Describe a vacuum arrester.

11. Explain the reason for placing an impedance in connection with the lightning arrester.

12. What is the purpose of the globule of low-melting alloy in the Western Electric Company's arrester?

13. Why are not fuses good lightning arresters?

14. What is the proper function of a fuse?

15. Make sketch of a mica slip fuse.

16. Define _sneak currents_.

17. Make a diagram of a sneak-current arrester and describe its principles and working.

18. Describe a heat coil.

19. Sketch a complete line protection.

20. Where is the proper position of the fuse?

21. Which wires are considered exposed and which unexposed?

22. Why is it not necessary to install sneak-current arresters in central-battery subscribers' stations?

23. Sketch and describe the action of a combined sneak-current and air-gap arrester, as widely used by Bell companies.

24. Describe the self-soldering heat-coil arrester.

25. What is the purpose of ribbon fuses?

26. What is a drainage coil?

REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 317--386

1. What is a central office?

2. What are (_a_) subscriber's lines? (_b_) Trunk lines? (_c_) Toll lines?

3. For what purpose is the switchboard?

4. Give short descriptions of the different cla.s.ses of switchboards.

5. How are manual switchboards subdivided? Describe briefly the different types.

6. Define A and B boards.

7. What is a call circuit?

8. What kind of calls are handled on a toll switchboard?

9. Give drop symbol and describe its principles.

10. What is a jack?

11. Make a sketch of a plug inserted into a jack.

12. Give jack and plug symbols.

13. What are ringing and listening keys?

14. Show symbols for ringing and listening keys.

15. State the parts of which a cord equipment consists.

16. Show step by step the various operations of a telephone system wherein the lines center in a magneto switchboard. Make all the necessary diagrams and give brief descriptions to show that you understand each operation.

17. On what principle does a drop with night-alarm contact operate?

18. What is the advantage of a.s.sociating jacks and drops?

19. Describe the mechanical restoration as employed in the Miller drop and jack.