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Variac safety

At 7:06 AM -0800 1/10/99, William Beaty wrote:
Maybe you'll want to add a 1:1 transformer to provide isolation from
ground. Depending on the internal circuit of the variac (and possible
miswiring of the electrical outlet,) there might still be 120VAC on your
electrodes relative to ground. If the variac's "common" is not referenced
to the neutral line of the AC outlet, and a student leans against a
grounded metal lab bench, ZAP!

I would strongly advise AGAINST using any 'Variac' that is not equiped with
a three-wire (grounded) cord. An unpolarized cord has a 50-50 chance of
having the output 'floating' at 120VAC and should be considered to be
deadly!

A school was disposing of some of these 'old' outdated variacs, but I
'salvaged them and added three wire cords, taking care to get the Neatral
and Hot lines connected properly.

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