A number of years ago I was doing a mechanical appraisal of a carousel
that had the trolley wheel type of communtator.  I don't off the top of
my head recall which machine, but I do recall that the pick-ups were
genuine streetcar trolley wheels.  They ran on three circular metal
rails under the sweeps.  The bearings were brass bushings, and were in
pretty good shape.  At a maximum of five rpm, it would take a
substantial amount of wear to cause any arcing problems.

It's possible that the carousel had been the property of a traction
company sometime in the past.  It's the type of thing that drives
electrical inspectors crazy now.  I've supervised the installation of
carbon brush and slip ring pick-ups on a number of machines over the
years to satisfy the inspectors.  Some of the smaller machines had one
single-phase non-grounded circuit for the lights.

Bruce R. Pier