Open HV Probe 40kV

[james_s]

I think some perspective is needed when evaluating this sort of thing. Would I use a home made 3D printed HV probe to measure the primary of a distribution pole pig or a 50kVa 150kVp xray transformer? Heck no, but for the sort of hobby HV stuff most of us are likely to encounter? Sure, why not? I played with CRT flyback transformers and neon sign transformers for many years using various scraps of plastic and strings of 1/4W resistors before I got a proper Fluke HV probe. It is seriously over-engineered for typical hobby stuff but it came in handy when I wanted to measure the output of MOTs and later the 4160V output of a pole pig we were using to power a HV series streetlighting regulator used for testing some products I was involved in. These sort of not only high voltage but high energy things is where it's worth splurging on the real deal.

[trobbins]

Yet if someones scope is inadvertently floated due to a poor or NO mains earth there would be no protective gain.

I am a fan of redundant protective earth connections.  Extra effort, but making any such measurement requires a set of precautions when setting up.