Is it advisable to make a differential measurement by using N2142A 10:1 75M Hz passive probe after removing the Earth of the Oscilloscope ( Powering the oscilloscope with a 2 wire cable, Ph, Ne without Earth) ?
If you do that, the chassis of the scope will be at the potential of one side of your differential signal. That includes the BNC outer conductors, digital interface outer conductors and exposed screws and metal. Even if the voltage level you are probing is not hazardous, floating the earth ground will disable one of the redundant safety features of the product protecting the user from line voltages.
This is the kind of thing that make safety engineers really animated.
Might I suggest using two probes and two channels to probe the differential signal with math to display the difference (ch1-ch2).
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