"Mark D. Zacharias" wrote in
:


wrote in message
oups.com...
WARNING... DANGER.... what is the point of floating the AC ground on
the scope, it is not only dangerous, but totally unneccessary as long
as the equipment that you are troubleshooting is being powered via an
isolation transformer..... that is the whole reason to use an
isolation transformer so that things like a hot chassis television
power supply can be easily hooked up to properly grounded test
equipment without making sparks fly and exposing yourself to
unneccessary hot ground hazards... keep the safety ground (3 prong
plug) connected on your test gear... in a large shop or manufacturing
and testing facility that has accountability to OSHA, disconnecting
the safety ground for any reason is a flagrant and dangerous
violation. electricitym
.
.
.


I agree - isolation is best, but if the 'scope has a 3-wire power
cord, with a properly grounded chassis, and the outlet is properly
grounded, should you not be able to just use the positive probe of the
'scope to look at the primary, and not even connect the test lead
ground wire to anything?


Mark Z.




Not for the primary side of switchers.There is no "ground" for those,the
low side is a "common",and not connected to true earth ground,and it can be
elevated up to -170VDC .Some switchers use a doubler arrangement for 120VAC
operation and reconfigure for 240VAC operation.

Tektronix used to have a great booklet about isolation and why certain
methods like "ground-busting" should not be used.I used to include one with
every scope that I serviced that arrived with no ground pin on the plug.
Maybe they still have it,I do not know.

--
Jim Yanik
jyanik
at
kua.net