The ground clip for an oscilloscope lead is normally connected within the instrument to the power supply earth, and there are surprising circumstances where this could matter. The situation is very well explained in "EEVblog #279 – How NOT To Blow Up Your Oscilloscope!"
Leads with galvanic isolation are very expensive, so, is there a good home-brew design or kit available? I realise that protection against high voltages might put this outside the home-brew area, but one for lower voltages would protect against dangers, such as that, described by Dave Jones in the EEVblog, of destroying the on board regulation of an Arduino via the ground connection of a USB lead.
Answer
Another choice is if your have a multi input 'scope, take two leads, connect their grounds leads together (and tape if needed to prevent shorting) and then use one as "signal" and the other as "ground" and use the A + (inv. B) functions of your scope to measure the signal and to remove the ground signal. It means you use more leads and can interfere with some scope functions. BUt it's another choice for you ...
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