In message <4.1.19990216100449.03b16750@192.168.0.1>, dave vanhorn
<dvanhorn@CEDAR.NET> writes
>I'll concede that there are times when floating the whole bench is
>waranted, and as long as EVERYTHING is floated, then you're ok.. but you
>STILL need to float the DUT relative to the bench.  The <ONE> time I had to
>float the scope, was for a very touchy measurement on the hot side of a
>switcher, where there was enough current circulating in the bench ground to
>fuzz the waveform.. I have a cheater plug for that. Still, it's safe, since
>the DUT is on isolation.

I'll explain my situation a little further, all the benches in our
workshop are wired the same way. There are a number of different sockets
(to account for old style plugs - hardly ever seen now), these are for
the DUT and connected via an isolation transformer and a double pole
isolation switch. There is one extra 13A socket mounted seperately, and
not isolated or switched, and this is used for the oscilloscope or a
monitor TV if repairing a VCR or satellite receiver. Aerial sockets for
the benches are isolated ones to avoid any earth connections through
those, thus providing an earth free environment.

>The point is, that as long as the DUT is on an isolation transformer, you
>don't have to remember any special systems, or make any lethal
>assumptions.. You, and visitors who don't know any special rules are also
>safe. Suppose I needed a power cable one evening, borrowed your scope power
>cable, and accidentally replaced it with a different one with an intact
>ground.. BZZZT.. Barbecue Mark.


BTW, my scope doesn't have a plug-in mains lead :-), in fact out of the
seven scopes I have access to (both at work and home), only one of them
has a plug-in lead - that's a Philips one.
--

Nigel.

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