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James Sweet

h wrote:
Actually, it is not a transformer.

It is ONE coil of wire connected across the AC supply with a variable
tap. Output is tied between tap and (Hopefully) neutral of the AC
input.

I think you should read up on autotransformers. Variac is a trade name
for a variable autotransformer, and they are in fact transformers. The
output of most of them can be adjusted *above* the incoming line
voltage, standard is about 10%. The one I have sitting here accepts 120V
input and outputs 0-140V so it is clearly a transformer.

For a bit more detailed info on the subject here's an article.

http://en.wikipedia.org/wiki/Variac