[Eliot Ness]

........wondered about the statement on the end "One side common to line and load".  Really what are they saying?......

A common variac does not provide isolation as this general diagram shows (neutral is common to the both line and load):

[Image: http://www.afcaforum.com/attachment.php?id=53827]

Unless you buy something like a PR57 or BK 1655 that has a built in isolation transformer you'll need to use an isolation transformer in-line with a variac for true (and safe) isolation.

I guess it bears repeating for others that when you buy an isolation transformer don't automatically assume it is isolated.  Ohm it out with a meter (while unplugged of course) to make sure everything is isolated.   Some recent medical grade isolation transformers are actually a leakage reduction transformer.

Like morzh I bought a Dale IT400 and while checking it out discovered like he did that it had a jumper that had to be removed to make it an isolation transformer.  Morzh documents his experience here:

http://www.philcoradio.com/phorum/showth...p?tid=4698