Complete noob question from not a noob. - Measuring Mains AC with Oscilloscope

[tautech]

i know this is been answered, and i am a noob. but i read in my books...NO you should never measure mains AC with a scope, unless you use something called a wal wart...or risk buring your scope out..

Quite incorrect.

No problem for "experienced" operators, but never recommended for oscillo-noobs.
The fact remains; why put a scope to mains "just" to see a sinewave, it's not worth the risk.

[vk6zgo]

This is the end of a power cord of a DVD that doesn´t have the 3rd pin (ground). I didn´t used the ground aligator to the neutral just because will be redudant. It is already connected to the mains power panel neutral BAR. But, of course, i previously detected with my multimeter continuity scale, wich wire is fase and wich wire is neutral!

Bear in mind that neutral is very rarely at ground potential, and that large currents can flow if it is connected to earth.

You must read learn and inwardly digest the "praxis" references in https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/ Failure to do so is likely to result in loud noises followed by deathly quiet and foul smells.

I believe ftonello was pointing out that in order to get a quick look at the Active line,it is not necessary to connect the "ground clip" to anything.

At 50/60 Hz,the chassis earth of the Oscilloscope provides an adequate return path via the phase/PE connection at the "meter box".
This will cause a miniscule current to flow in the PE line,which is insufficient to upset the Authorities,or your RCD.

The very long return path will cause errors in displaying higher frequency transients,"crud",etc, on the Mains,and,of course,it won't work with 'scopes which are not Mains powered.

[ftonello]

This is the end of a power cord of a DVD that doesn´t have the 3rd pin (ground). I didn´t used the ground aligator to the neutral just because will be redudant. It is already connected to the mains power panel neutral BAR. But, of course, i previously detected with my multimeter continuity scale, wich wire is fase and wich wire is neutral!

Bear in mind that neutral is very rarely at ground potential, and that large currents can flow if it is connected to earth.

You must read learn and inwardly digest the "praxis" references in https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/ Failure to do so is likely to result in loud noises followed by deathly quiet and foul smells.

I believe ftonello was pointing out that in order to get a quick look at the Active line,it is not necessary to connect the "ground clip" to anything.

At 50/60 Hz,the chassis earth of the Oscilloscope provides an adequate return path via the phase/PE connection at the "meter box".
This will cause a miniscule current to flow in the PE line,which is insufficient to upset the Authorities,or your RCD.

The very long return path will cause errors in displaying higher frequency transients,"crud",etc, on the Mains,and,of course,it won't work with 'scopes which are not Mains powered.

Yes you´re right vk6zgo...and as tggzzz said, i know about the risks and the noise...(very good read material by the way) and this practice is not recomended for a long time nor doing by begginers... just showing that you´ll not blow your scope...


And what about DAVE or someone, reproduce with schemmatics what this guy did on a 3-phase measuring with scope in this video?

[Porch]

I picked up a PINTEK DP-25 for about $200 on ebay.  If you want to measure AC mains/high voltage, this is the way to do it.

Now to figure out just what this Honda generator is trying to do. 

[tggzzz]

Yes you´re right vk6zgo...and as tggzzz said, i know about the risks and the noise...(very good read material by the way) and this practice is not recomended for a long time nor doing by begginers... just showing that you´ll not blow your scope...

Accepted, and thanks.

I'm always aware that a less experienced person may read the Nth post in a thread and not appreciate all the context and/or not understand the limits.