In article , Gary Coffman says...

A *floating* dual trace scope. Current can be measured with
a sampling resistor.

Or one that has isolated differential preamps, like one of mine does.
Ordinary scopes use unbalanced inputs, with one side tied to chassis.
Trying to measure phase voltages and currents with one made that
way will give you a *hot* chassis, which is a serious shock hazard.

The plug-ins for the 7000 series tek scops *look* like they're
isolated ground. They have the bnc shell isolated from the
front panel with a teflon insulator. But this is to minimize
internal ground loops. The low side is indeed tied to power
common. But the appearance has fooled many a grad student....

Jim

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