Fw: Re: Floating scopes, isolation xformers.


arthurok <arthurok@...>
 

----- Original Message -----
From: "arthurok" <arthurok@ameritech.net>
To: "Chuck Harris" <cfharris@erols.com>
Sent: Thursday, March 23, 2006 11:39 PM
Subject: Re: [TekScopes] Re: Floating scopes, isolation xformers.


i never said it was a good idea
if you read the posts other people have done it to in a pinch
if the potential between earth and the scope case is
under lets say 30 volts rms or 48 volts peak
you arent taking much of a safety risk
i think thats the application ibm used the isolated
switch for on the 454 to make measurements where there was a
small voltage differential between test point ground and
scope line cord ground
lets say you had 6 volts rms between the test lead ground
and scopes earth ground under those conditions
you would get alot of current flowing through the probes
wire shield and maybe smoke it
you should always use an isolation transformer when working with a hot chassis device
unless i have to hook up a scope or a signal generator i dont
my meters are floating.
i wouldnt float the scope at a very high voltage because it might cause internal breakdown
ive never floated it higher then the 120 vac line and that was done with great care my scope is grounded right now
FLOATING THE SCOPE CASE ESPECIALLY AT A VOLTAGE THAT COULD BE LETHAL IS A BAD IDEA
I SEE THAT OTHERS HAVE DONE IT WITH GREAT CARE WHEN AN ISOLATION DEVICE WAS NOT AVAILIBLE. AS FAR AS IM CONCERNED HOT CHASSIS DEVICES ARE CRAP AND UL MAKES IT DIFFACULT TO GET ACCEPTANCE ON THEM
MOST MODERN TVS ARE FULLY ISOLATED NOW
EVEN THE CHEAP ONES .
y
----- Original Message -----
From: "Chuck Harris" <cfharris@erols.com>
To: "arthurok" <arthurok@ameritech.net>
Sent: Thursday, March 23, 2006 10:50 PM
Subject: Re: [TekScopes] Re: Floating scopes, isolation xformers.


No, it doesn't... Well, not so that it will help you much. The
scope probes connect directly to the metal on the scope's case, and
the scope's case connects to the big round pin on the power cord.

If you disable the round pin (bond wire), you will have your
scope "floating", but all the metal in its body, and the ground
clip on the scope probes will still be connected together. If
you happen not to be isolated yourself, bzzap! You'll be just
another bug in the old bug zapper.

It's your life, but please, stop trying to convince anyone that it
is a good idea.

-Chuck Harris

arthurok wrote:
the scope has an isolation transformer built into it
if you exceed the primary to secondary breakdown voltage of it you will damage it and the scope will nolonger be floating
----- Original Message -----
From: "msauve2" <mikes@flatsurface.com>
To: <TekScopes@yahoogroups.com>
Sent: Thursday, March 23, 2006 5:20 AM
Subject: [TekScopes] Re: Floating scopes, isolation xformers.

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