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Message-ID: <55998CC5.9020509@sbcglobal.net>
Date: Sun, 05 Jul 2015 13:00:05 -0700
From: "Girvin R. Herr (gherr375 AT sbcglobal DOT net) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
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To: geda-user AT delorie DOT com
Subject: Re: [geda-user] OFFTOPIC: New toy...
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Reply-To: geda-user AT delorie DOT com

Peter,
Another option I used in the past was to use the scope in differential 
mode, which is to configure one of the two input channels to be inverted 
and use two equal probes.  The only concern then is to not exceed the 
scope's common mode voltage.  The probe grounds are connected to chassis 
ground, one probe is connected to the circuit under test common (i.e. 
neutral) and the other probe is connected to the signal under test.  
That works fine, but it requires 2 identical probes and a scope that 
will allow differential configuration.
HTH.
Girvin Herr


On 07/05/2015 07:16 AM, Peter C.J. Clifton wrote:
> On 2015-07-03 23:16, Evan Foss (evanfoss AT gmail DOT com) [via 
> geda-user AT delorie DOT com] wrote:
>> Ok. It is odd how many people I know use non-isolated probes on things
>> like the 3PH power to the motor.
>
> My background was power electronics at university, so it seems 
> obvious.. (likewise, I'm also sure I've accidentally grounded circuits 
> with an oscilloscope ground probe before now).
>
> A 100:1 non-isolated probe should be good for probing mains, motors, 
> but obviously the ground needs to reference a chassis earth, not any 
> other line (or neutral) conductor.
>
> Peter
>
>