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We all know what happens when we ground a regular oscilloscope probe at the wrong place: a short. There are two main points to consider:

1) All channels share the same ground plane, so we can't take 2 or more simultaneous measurements referenced to different "grounds".

2) The scope's ground plane is directly connected to the center pin on oscilloscope's AC power cord, which is probably connected to the ground of the equipment we are probing, preventing us from using any other reference than the "official" ground itself, otherwise we will have shorts and possibly fireworks, in more severe cases.

There's nothing to be done about point 1, but about point 2, why not simply disconnect the center ground pin on scope's AC cord and leave it floating? I personally do that with my older scope. When using channel 1 only, I can freely move my ground hook everywhere in my circuit, and I never had any problems, apart from some 60Hz noise, but this is expected, I guess, since the whole scope is floating and subject of all kinds of noise.

So, apart from the increased noise, is that harmful to leave the scope ground floating? What else am I loosing doing things that way? In which situations my practice will bring me serious trouble? Does that damage the scope in the long term?


marked as duplicate by pipe, Community Aug 2 '16 at 13:16

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    \$\begingroup\$ Possible duplicates (and a variety of answers) here and here. \$\endgroup\$ – Cheibriados Aug 2 '16 at 13:05

That's called "floating the scope". The problem is the scope chassis is now floating. If you connect the ground lead to...say...that 220VAC line on your DUT, now your scope chassis is at 220VAC. You can easily become the path to ground by touching the scope chassis and something else at the same time.

As long as you are very aware of what you're doing, floating the scope can be done. However, the potential for a mishap is quite high, especially if other engineers come along and don't realize the scope is floating.


Connecting to the utility mains without a floating scope. And attempting to measure voltages at line potential.

Remember how the fried ground clip looked after all the sparks were gone?

Now, with a floating ground o'scope : I wouldn't like to see you looking like the fried ground clip after you touched the o'scope chassis (case).

There would be the utility incoming line potential between your o'scope chassis and earth (you).


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