On Sun, 13 Jun 2010 23:16:44 +0100, "Dave Plowman (News)"
wrote:

In article ,
Michael A. Terrell wrote:
If using a proper isolating transformer, there will be no reference to
ground even with a 'live' chassis. The only way to get an electrical shock
is to touch both outputs from the transformer.


Not true. You connect the chassis of the UUT to the test equipment,
so ANY voltage you contact inside the UUT is referenced to ground.

Why is the test equipment grounded?
Perhaps you are a little inexperienced. There was a time when
virtually ALL test equipment came with a two wire (ungrounded) cord.
Then it was decided that having technicians electrocute themselves was
undesirable from both efficiency and moral viewpoints. As a result,
signal generators, oscilloscopes, frequency counters, alignment
generators, etc all were supplied with a 3-wire cord. Thus, when an
oscilloscope was hooked to a live chassis TV the probe ground burst
into flames rather than the technician falling to the floor in cardiac
arrest. Of course, there were those brave (or foolish) souls who cut
off the ground pin on the power cord to save a few dollars. While
others might disagree, I feel that using an isolation transformer is
preferable to losing my life.

PlainBill