Depending on the commutator design, this may include the brushes shorting together adjacent sections and hence coil ends momentarily while crossing the gaps.
By means of a commutator the mercury vapour and helium tube is placed in circuit for two-thirds of a revolution and the neon tube for the remaining third.
Brushes eventually wear out and require replacement, and the commutator itself is subject to wear and maintenance (on larger motors) or replacement (on small motors).
