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Variac should have been spelled with a "c", not Varik. My mistake

Steve

That must be why they are used to power electric shaver outlets in bathrooms ;-)

Just joking, we are in agreement, only that you went a bit over the top maybe.

Isolation transformers can be used safely, allowing one to make measurements almost impossible any other way.
It just requires people to know what they are doing, otherwise evolution will happen.

ST

I have a nice isolation-variac unit I built, but hardly ever use. With differential inputs and diff probes there really isn't much need for it. I suppose if you work on those old hot chassis TVs maybe.

Where I used to work they had battery operated LeCroy scopes which they used when they wanted to be floating, but that was more to break ground loops for reducing measurement noise than to have the ground of the scope at some high potential.

You must always take care when working with high voltages... it's not the place to be throwing leads around without thought.

There's nothing inherently wrong or dangerous about floating a measurement instrument... every portable DMM is that way... it is when you have common grounds, exposed metal chassis parts, high voltages or energy that things start requiring thought. Go into what you're doing with a plan!

Peter