On 2012-10-10, Jon Danniken wrote:
On 10/09/2012 07:24 PM, Pete C. wrote:

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.

I've seen some at least with the metal core.

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.

I have a triple-ganged variac stack that also uses a metal shaft. The
plate on each variac that holds the wiper is phenolic, providing
isolation from the voltage on the wiper.

Is that genuine Variac (General Radio) or a Superior Electric
Powerstat, or some other brand? It may be that some models have the
insulated shaft and others the insulated hubs within each brand.

Enjoy,
DoN.

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