1. Most of a DC machine’s problems occur in the armature (page 57).
2. Lacquer thinner is a good liquid for cleaning a commutator (page 58).
3. An open armature coil may cause dead spots (page 58). T_ F
4. Burned commutator segments spaced equal to the distance of two like-polarity brushes indicate an open equalizer (page 58). T_ F
5. Brushes are all interchangeable if they fit the brush holder (page 59).
6. Name two types of current flowing in a brush’s conduction zone (page 60).
7. Split brushes reduce the circulating current in the conduction zone
(page 61). T_ F
1. A spiral groove cut in a commutator improves its performance (page 61).
2. All brushes in a multiple brush holder should carry the same number of amperes (page 62). T_ F
3. All motors should have their brush boxes the same distance from the commutator (page 62). T_ F
4. Uneven distance between brushes can affect commutation (page 62).
5. Spring tension must be the same for all brushes (page 63). T_ F
6. High amperes require heavier spring tension (page 64). T_ F
7. Brush shunt wire size isn’t important because the brush box will carry the current (page 65). T_ F
8. How can uneven commutator segments be detected (page 65)?
9. Name two causes of excessive brush dusting (page 65).
10. Gray brushes are better than black brushes for (page 66)
a. high amperes.
b. less wear.
c. low amperes.
18. Give the formula for finding brush current density (page 66).
19. Silicone grease should be used on DC motors (pages 66-67). T_ F
20. Why should brushes be properly seated (page 67)?
21. What will cause a brush face to have a flat black color (page 67)?
22. The final brush setting for a DC motor is the spot that has less than
1 /2 volt between segments (page 69). T_ F
23. Moving the brush holder—one segment at a time against rotation— until there is the least amount of sparking is called the black band adjustment for a motor (page 69). T_ F
24. Generators should always have their residual magnetism restored—by applying DC to Fl and F2—after AC has been used to set the brushes on neutral (page 69). T_ F
25. Name two ways to test an armature on site (pages 70-71).
26. Name two symptoms of a grounded shunt field (pages 71-72).
27. All coils should be replaced when an ohmmeter reading is between
1 and 50 megohms (pages 72-73). T_ F
18. A circuit that is being tested for a ground should be isolated from all other circuits (page 73). T_ F
19. Why are shorted turns in the series field circuit usually very obvious (pages 76-77)?
20. A compound wound DC motor will run if the series field is not connected (page 78). T_ F
21. How is a compound wound generator affected when the series field is not used (page 78)?
22. The commutator is a high-leakage circuit (page 79). T_ F
23. Why are interpoles subject to problems if the armature is overheated (page 80)?
24. Why should AC and a resistor be used to supply AC for testing (page 82)?
25. DC will cause high current to flow in shorted turns (page 83). T_ F
26. Why is it important to draw a schematic of a complicated circuit before testing it (page 84)?
27. Name four problems that occur in the shunt field (page 85).
28. An ohmmeter will show a lower resistance reading when the test is close to a grounded coil (page 88). T_ F
29. Why is an equipment ground not recommended for DC machines (page 88)?
30. A coil with shorted turns will show a
reading than the rest of the coils (page 89).
a. higher resistance
b. lower resistance
31. Dividing the test voltage by the number of coils being tested will give the approximate voltage found across each coil—if none are shorted (page 89). T_ F
32. difference is allowable when comparison testing coils with an ohmmeter (page 89).
18. A or — Of 
difference is allowable when comparison testing coils with a voltmeter (page 89).
a. 2%
b. 5%
c.