Editing Commutator (electric) (section)

=== Brush holders ===
[[Image:Commutator - Crocker-Wheeler Carbon Brush Gear (600dpi).png|thumb|400px|Compound carbon brush holder, with individual clamps and tension adjustments for each block of carbon<ref>[[Hawkins Electrical Guide]], Theo. Audel and Co., 2nd ed. 1917, vol. 1, ch. 21: Brushes and the Brush Gear, p. 307, fig. 335</ref>]]
A spring is typically used with the brush, to maintain constant contact with the commutator. As the brush and commutator wear down, the spring steadily pushes the brush downwards towards the commutator. Eventually the brush wears small and thin enough that steady contact is no longer possible or it is no longer securely held in the brush holder, and so the brush must be replaced.

It is common for a flexible power cable to be directly attached to the brush, because current flowing through the support spring would cause heating, which may lead to a loss of metal temper and a loss of the spring tension.

When a commutated motor or generator uses more power than a single brush is capable of conducting, an assembly of several brush holders is mounted in parallel across the surface of the very large commutator. This parallel holder distributes current evenly across all the brushes, and permits a careful operator to remove a bad brush and replace it with a new one, even as the machine continues to spin fully powered and under load.

High power, high current commutated equipment is now uncommon, due to the less complex design of alternating current generators that permits a low current, high voltage spinning field coil to energize high current fixed-position stator coils. This permits the use of very small singular brushes in the [[alternator]] design. In this instance, the rotating contacts are continuous rings, called [[slip ring]]s, and no switching happens.

Modern devices using carbon brushes usually have a maintenance-free design that requires no adjustment throughout the life of the device, using a fixed-position brush holder slot and a combined brush-spring-cable assembly that fits into the slot. The worn brush is pulled out and a new brush inserted.

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