A. The scale on the copper electrode after it has cooled off is a non-conductor of current, and acts as a blind gasket between the carbon and the copper electrode. Unless this scale is removed, the current cannot pass between the points of carbon and electrode and you cannot, therefore, have a light. When the dynamo fields are compound wound, it is unnecessary to clean scale from copper electrode oftener than once a week, at which time copper electrode should be removed from holder and all scale cleaned off. (With compound wound dynamo fields the cab lamps will continue to burn when head-lamp is extinguished by lifting carbon by hand.)
15. Q. How should the copper electrode be trimmed at the point?
A. The copper electrode should have about one-eighth inch surface on the contact point.
16. Q. How far should the copper electrode project over the holder?
A. About one inch.
17. Q. Should the electrode be raised up to one and one-half inches, what might happen?
A. If the copper electrode was run at a point so near the clutch, the intense heat of the arc might do damage to the top carbon holder and clutch.
18. Q. What regulation should be given to the tension spring No. 93 of the lamp, and why?
A. This tension spring, No. 93, should be regulated when the current is off the lamp and should be adjusted only tight enough to pull the magnet yoke up against the top stop lug on the side of lamp column.
19. Q. If this tension spring was tightened too tightly, what might happen?