The commutator of a DC machine is usually made of copper bars separated by?

The commutator of a DC machine is typically constructed with copper bars that are separated by mica. Mica serves a crucial role in this assembly because it is an excellent electrical insulator, which prevents electrical short circuits between the conductive copper bars. Additionally, mica can withstand high temperatures and has good mechanical strength, making it a suitable material for the rigorous conditions present in a DC machine's operation. This property of mica helps to ensure reliable performance and longevity of the commutator system, thus contributing to the efficiency and effectiveness of the motor or generator.

Other materials, such as carbon, fiberglass, and steel plates, do not offer the same combination of electrical insulation, thermal resistance, and mechanical properties that mica provides, making it the preferred choice for separating the copper segments in a DC commutator.