On 2012-10-10, Karl Townsend wrote:
Xmas came early this year, a couple a great big variacs showed up in
the mail today. Thank you Santa Pete.

These monsters have a common shaft so two can be turned in unison,
nice feature as i need to hook these up 220. Just want to verify the
hookup: The hot lead on each variac to each leg of the 220, the wiper
for each variac to the load, tie the nuetral on each variac together
and to nothing else (not ground that is). Correct?

I would tie the neutral of each together and to the supply
neutral for safety against imbalance. Otherwise, you have it right.

Note that many powerstats (these are not General Radio Variacs,
based on the photos -- use "variable autotransformer" for a generic
term) as well as genuine Variacs have extra taps, so you can boost the
line to something like 140 V with a 120 V input per autotransformer.
And because these can be wired to increase CW or CCW, they often have a
lower tap as well, so they are (in series) 20V, 100V and another 20V if
you want boost. You probably don't want boost.

Beware that a big knob on these (especially the steering wheel
style which some have) tempts small hands. I remember a case when I was
in El Salvador, and encountered a setup of US audio equipment all
plugged into a 240V variable autotransformer (I think that it was
another Powerstat, FWIW) with power coming in to the center tap
(which exists on the 240 V ones, so they could adjust to make up for the
(at that time at least) rather variable voltage. Anyway -- a kid about
six years old saw it, his eyes lit up, he ran straight to it, and spun
it clockwise -- frying the selenium rectifier in a Magnecorder.

What I would suggest is to set it and then remove the knob -- or
at least loosen the setscrews so it spins freely -- unless you need to
adjust it frequently. I don't remember for sure far enough upthread,
but I think that this was just to make something designed for a
different voltage work, and not a need for frequent adjustment.

Enjoy,
DoN.

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