Question

Spacing between the brushes for a 4-pole machine in terms of commutator segments for 12 conductor segments is _____

(a) 48

(b) 3

(c) 2

(d) 6

This question was posed to me during a job interview.

This intriguing question originated from Brushes and Commutator Assembly topic in portion DC Machines of DC Machines

Answer 1

Right option is (b) 3

To explain I would say: The spacing between adjacent brushes in terms of the commutator segment is ratio of number of commutator segments with poles for a given DC machine.

C/P= 12/4= 3.

It may also be noted that C/P need not necessarily be an integer.