Ecnerwal wrote:

In article ,
"Pete C." wrote:

Hmm ... another thing to watch out for. At least the General
Radio Variacs used shafts covered by a black plastic (Bakelite, perhaps,
given when they were designed) and there was no attempt to insulate the
center of the rotor plate from the shaft

The ones I've seen (Variacs) were solid phenolic (probably cotton or
linen based) - a pretty good, pretty strong insulator, with no metal in
the shaft at all. An early composite, common in electrical items.

This bank had a metal shaft connecting the sections to the motor drive.
I don't recall any particular insulation for that shaft at the drive
end.