Thanks JW. Perhaps the clearest explanation of correct ‘scope/mains practice I’ve heard.

Clear and precise explanation, going into detail that is easy to understand.
Thanks for your effort to share your knowledge with the rest of us John.

Very clear and thorough explanation. I 'sort of' understood this before, but now I 'really get it.' Thanks.

Find this man ace, wish I had thought of been an Electrition,, love your work immensely 😀

My second lesson in two days on using a scope on mains - Play With Junk also talked about the dangers when he was probing a linear power supply. But your video gave far more detail on the different scenarios.

Hi John, Just watched this video. You can use the two channels of the scope and then there is a setting to display the difference between the two channels. Then you don't go anywhere near the external connection. No need to connect to the outside connection of the BNC connector. Just plug one channel to one side of the supply and the other channel to the other side.

Love your videos with clear reasoning and good solutions.

If you are new to isolation transformers, research the subject thoroughly. Before you buy one, understand that not all isolation transformers are intended to be used in a test bench application. Some will pass the mains earth to the secondary coil by bonding the neutral lead to the primary earthing. This type is not suitable, and will require modification before use. Also, a cheap variac autotransformer alone will not work. It will not provide Galvanic isolation. Therefore, it still will require the use of a properly mains earth isolated isolation transformer.

Saw your other video, was wondering myself about the details, so thanks for making this video!

I built a circuit that used high value resistors for a voltage divider, then an isolation amplifier to keep the high voltage away from the oscilloscope. I find it especially useful for measuring non-sinusoidal waveforms like modified sine wave inverters.

Thanks John

Thank you for the great explaination. Some great points. 👍

Hi John. Love watching your videos and you indeed one very clever bloke! 👍🏻. I’m looking for a handheld oscilloscope to be able to see the waveforms for 230v AC and also DC voltages up to 48V. This would be for testing the outputs on portable generators & DC to AC inverters. These will be installed on boats as some of these generators and inverters don’t produce and very nice sine-wave and cause issues for the boat owner. It would be really nice to be able connect a scope up to these and see if they are actually producing a nice waveform so I can 100% prove that it is their inverter or generator. Some of these inverters do actually say they are modified sine wave but some don’t. I’d like to know which handheld meter can do this safely and would I still require a voltage divider. Many thanks. 👍🏻

Thank you JW first time I've understood the whole issue

Fabulous video; beautifully, clearly explained. thank you very much. The "fairly fatal" amused me! :D

Very accurately explained! There are so many ways you can destroy an osciloscope or the equipment you are probing. This video  should be watched by anyone thinking about buying and using an oscilloscope. It should be watched BEFORE using it. Unfortunately for my cheap China USB scope, I watched your video afterwards.

My favorite 'other' option I've seen used is to simply add a loop or two of loose insulated wire to any magnetics already present in the circuit. While the turns ratios and actual voltage levels of the circuit will still be unknown as far as the scope readings, this does create a small scaled, isolated voltage that will allow you to see the AC waveform.

As always, thorough simple arguments and solutions.

Very good.  I did not know about this at all!  And now... I need to go shopping for an isolation transformer!