Re: "Normally the ground lead of a scope probe is connected to the ground of the scope and this ground is connected to the safety ground of the AC power input.? One can remove this safety ground with adapter on the AC plug and then connect the scope to the AC mains."

[red added by me for emphasis.]

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Of course this ignores any EMI filters from hot to the case...EMI filters have capacitors, older EMI filters have rather high value caps.

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Some genius decided to solve an AC Mains induced audio hum in a temporary edit suite by using a NEMA 15-5R to NEMA 1-15P, 3 to 2 AC adapter. [AKA "Ground Cheaters]

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Sure solved the hum problem and placed a female teaching assistant in the hospital overnight for observation after she received a nasty shock. If an EMT hadn't been present the coed probably would have died because no one but the EMT knew CPR.

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An engineer lost his job and was blackballed, he barely avoided criminal charges. He actually faced a grand jury. Things could have gone very badly for him.

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I'm pretty sure we don't have any "Ground Cheaters" in our home. And I have adapters for damn near everything.

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Feel free to use whatever power connection you like but please be aware there are members in this group who lack the experience to understand how dangerous your scheme is.

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I'd like to warn everyone to be aware the case? could be hot with 120V/240V (we have members from all over the world).?

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I use 120V:120V isolation transformers for such tests or a battery powered scope.

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Just be aware the use of "Ground cheaters" 3 to 2 adapters are flat illegal in Canada and some US cities have banned them.

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While every state in the US has adopted the National Electrical Code, states and local administrations are free to add additional safety rules. [And good luck finding out what the exact rules in your city might be.] I've heard Miami has outlawed 'Ground Cheaters" but wasn't able to wade through their online building codes.

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"These adapters are illegal in some jurisdictions, in particular throughout Canada."

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The state of Ohio has issued seven citations to Cleveland State University (CSU) for unsafe electrical conditions in the lab where associate professor??died last August after plugging in a defective fluorescent light through a two-prong adapter plug that left the lamp ungrounded. Experts say that the conditions that led to Mal's death were indeed unsafe, and some believe those problems are not uncommon at other American universities, suggesting other lab workers may also be at risk., CEO of the?, told?The Scientist?that the problem that killed Mal -- using a two-prong adapter in a three-prong outlet -- is common. "When you inspect labs," he said, "it's not unusual to find anywhere from one to seven that way."

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I am NOT a lawyer and I doubt if someone is injured or dies using your idea that you'd be held liable for either criminal charges or a civil tort, but who knows....lawyers are so damn inventive.

Again, I am not a lawyer, so what do I know about legal liability?

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This is a situation where a moderator or group of moderators need to decide "what unsafe posts do we delete." I might be a moderator/owner but after the last flame fest it won't be me.

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A friend suggested this program as it has normal oscilloscope display, phase (XY) Lissajous, FFT, and a signal generator.

"Visual_Aanalyzer_Freeware"

at

https://www.zeitnitz.eu/scope_en

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The FFT display is labeled "Frequency" for some unknown reason. It has a zoom function that is rather useful.

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At the moment our 240V AC Mains has 3.8% to 4.5% harmonic distortion. It varies randomly. I wonder what effect a few hundred thousand people turning on their coffee makers has.....

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I have a 240V outlet at my radio desk just in case I ever want to get serious about ham radio and add a 5kw RF amp. [yea right after hell freezes over] It's really for a special space heater an electrician friend located for me.

[That warmed my room from 68F to 75F in 30 minutes. I've found I don't tolerate cold as well at 73 as at 16. Bummer.]

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The phase, which indicates short term, "instantaneous," frequency variation, goes wild at ~6:30 about the time the harmonic distortion also goes nuts.

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I have a 10MHz GPS disciplined oscillator with a magic PIC 10MHz to 60Hz (zero jiter) that I feed into the vertical and attenuated 60Hz from the AC mains into the horizontal. The Lissajous "circle" jitters like crazy until ~9:00AM when it "stabilizes" [sort of] then goes nuts around 4:00PM until ~7:00PM.

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Yea I know I have some really odd hobbies that will probably kill me someday,

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And yes it's a bit hypocritical that I routine monitor the AC Mains, but I'm extremely careful, have designed interfaces that are as safe as I can make them and the outputs are "idiot proof."

I repeat, if all you want to do is look at the 50/60Hz Mains waveform, why? There is nothing interesting about a 50/60Hz 'sinewave.'

OK an oscilloscope is probably the wrong tool for this job. Consider a battery powered laptop operating on battery power with a resistive attenuator.

Laptop internal audio line inputs run anywhere from 5K to 50K.

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I'd go with a 10:1 attenutaor, high resistance to high, junction of high [tip or ring] resistance to low resistance to sound card hot in, low side of low resistance to neutral and sound card low [sleeve].

I'd place 6 1N400x diodes, 3 in series wired antiparallel. Anode of one string to cathode of the other string to limit the maximum voltage to ~2.1V.

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I like Dale aluminum shell resistors that can be mounted to metal. Ground the metal for safety.

I use 9k from hot to 1K with goes to neutral. I'd place a 10k pot across the 1k and adjust for 1V with a DVM.

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Record with a program like Audacity, a freeware program. I'm not familiar with freeware FFT software but Audadcity does have FFT, I have no idea how good it is.

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"Yes, Audacity does have an FFT (Fast Fourier Transform) display, which is accessible through the "Spectrogram View" feature, allowing you to visually see the frequency components of an audio file over time by utilizing the FFT algorithm to analyze the data;?you can also access a "Plot Spectrum" function to view a single snapshot of the frequency spectrum of a selection within your audio file, also based on FFT calculations.?

Key points about Audacity's FFT display:

·??????????????????????????? Access:

To view the FFT display, go to the track menu and select "Spectrogram".?

·??????????????????????????? Function:

The spectrogram shows how the energy distribution across different frequencies changes over time.?

·??????????????????????????? Plot Spectrum:

To see a single snapshot of the frequency spectrum, go to "Analyze > Plot Spectrum".?

·??????????????????????????? Underlying Calculation:

Both the spectrogram and plot spectrum use the Fast Fourier Transform (FFT) algorithm to analyze the audio data

FFT will display the spectra with harmonics, the time display will show a normal waveform, which, unless there is more then ~10% harmonic distortion, probably won't be visible.

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Now for UPS 'quasi sine wave' outputs, the time display may well show you some really odd waveforms.

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I don't use Audacity, I use Adobe Audition, which has similar capacities but is not freeware. Way not freeware. Obscenely expensive.

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Please remember the dangers remain the same.

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Record the waveform, then disconnect the AC and play with Audacity.

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My rule of thumb is to stay connected to dangerous voltages only as long as necessary.

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We compared an expensive Rigol DSO FFT with a mediocre laptop for audio FFT, the cheap PC blew the Rigol away.

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Part of any measurement process is picking the best tool(s). That can be difficult with all the sales hype for scopes etc.

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I asked about age because at 14 I knew everything and took way too many chances. At 61 you've lived long enough to know your limits. So the age of someone I don't know becomes an issue when trying to offer technical help.

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I added a phone to a girl friend's (not romantic) bedroom. Hid the wiring, removed the bell, life was good, until the phone rang when I had one wire connection in my mouth while completing the other.

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Let's just say the sudden wetness at my crotch was the least of my concerns. 90V at 28Hz flowing through your mouth to your hands is an extremely interesting experience. I was 14 and my thinking was normal for a 14 year old, I didn't think far enough ahead.

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And yes I realize how dangerous that was and how lucky I was to only have wet pants.

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So age is a valid question when dealing with hazardous voltages.