I need to make some differential measurements on a device, but both nodes need to be floating from earth.
I found out the hard way that the negative clip of my oscilloscope voltage probes are connected to the mains earth conductor, but I don't have access to a differential probe.
I was wondering if there is an easy solution to this, and I figured this: inside the scope I have seen that the mains are only connected to a power, old style transformer, while the earth lead is screwed to the metal chassis. Since of course the transformer output is isolated from its input, I think that if I just remove the earth screw from the chassis and isolate the cable I can now connect my device to the scope, avoiding the pesky ground current that destroyed my first board.
The negative terminal I would hook to the probe clip is about 60V over earth, the maximum current it can source is just above 30mA. The input transformer can surely withstand a 60V offset, right?
I think that this is safe because the shell of my scope is all made of plastic, the only metallic parts are the BNC connectors and a couple of blade connectors that I use to calibrate my probes, but they should all be safe.
Is it ok to remove the earth connector from my scope to make such a measurement? I have seen this suggestion all over the web, so I think it must be safe, but I want to ask a board of professionals just to be extra sure.