A circuit connected to a nobreak disconected from main is a floating circuit?

[Airton]

I was watching this video about scope safety and begin to wonder if someone wants to probe a main earth safely:
Would be pratical and cheaper to connect the system that you want to probe in a nobreak disconected from the main (using the batery) instead of buying one of this active probes?

Video:

[Ian.M]

*NEVER* float a scope not inherently designed for floating use!

Engineers have died doing that!

See: https://www.eevblog.com/forum/testgear/ground-of-oscilloscope-always-connected-to-earth/

If on the other hand you propose to float the D.U.T, (device under test), yes, that's possible and usually safe for the scope, but remember that as soon as you connect the scope the isolation transformer's output becomes ground referenced, so the whole primary side of the DUT's PSU becomes a mains live safety hazard zone again.

[Terry Bites]

If you want to see whats going down the earth wire use a current transformer.