Brush, Third

A third brush is sometimes provided in a dynamo for regulating purposes. Applied to a series machine it adjoins one of the regular brushes and delivers its current to a resistance, to whose further end the regular circuit is connected. By a sliding connection the resistance is divided between the third brush circuit and the regular circuit, and by varying the position of this contact regulation is obtained. It is to be distinguished from the pilot brush used for determining the characteristic of the commutator, although based on the same general principles. IMG:8956969607833025625_092F70.jpg: Fig. 70. THIRD BRUSH REGULATION. 92   STANDARD ELECTRICAL DICTIONARY.