Floating Scopes

[johansen]

My hakko iron...

I lifted the ground and installed a neon lamp and 40k resistor

So it lights up when im soldering on live circuits.

[GnomeZA]

A lot of good info in this thread, but one thing overlooked now in 2023 are newer scopes like the Rigol DHO800/900 series come floated due to having a USB-C type power plug and a power brick from Liteon that is only 2-prong at the wall socket.  Sure, they include a separate grounding wire (with banana connectors at both ends) "for safety," but the fact the scope comes this way is a recipe for unsafe practices, especially here in Japan where 3-prong wall sockets are utterly impossible to find in most homes.  Indeed, here in Japan, the only time you'll see a ground is near a wall socket in a room where there is a toilet (Japanese love their electronic bidet devices), or a refrigerator in the kitchen.  They are almost always screw terminals for connecting bare wires that hang off the appliances or bidets. Any other place, which is the most likely place you'd be using a scope, the wall sockets are 2-prong only.  But even if they were 3-prong, the design of the power adapter is such that the user isn't FORCED to use a grounded wall socket plug.  That Rigol grounding wire is "optional" in that it isn't built into the main power cord.  That is a big issue.

Tektronix offers battery powered scopes which are basically floating devices, but even Tektronix cautions you about them, properly saying not to test voltages above 30Vrms or 42Vpeak.  They also warn against the use of Isolation Transformers as being "Dangerous."

https://www.tek.com/en/documents/technical-brief/floating-oscilloscope-measurements-and-operator-protection

But even if you are using less than 30Vrms (which is basically all I test, personally), grounding the scope provides a way to avoid Common Mode Noise on your measured waveforms.

Lastly, the Rigol DHO800 documentation that came with my scope doesn't even use terms like "floating," and references to Earth Ground are few, which mean that people searching the documentation for important safety info might miss the topic altogether or think they are safe to use their new 12-bit scope in a floated condition.

The thing is, that scope still has the outside part of the BNC all tied together, and the ground clips on all channels will thus be connected in parallel to the outside of the BNC.  So if you use multiple channels, and they are at different potentials in reference to each other (with low impedance), you will be causing a short by connecting your ground clip.

ie. I use one probe and the ground connector is connected to live, and I connect the other probe's ground connector to neutral.
Or I use a single probe and I accidentally have the ground connector connected to something that is not at earth potential and I touch any BNC connector on the scope (ouch time).

I looked into this because it seemed like a win, win over a handheld scope for example.
Use the Rigol and power it from a USB-PD power bank and suddenly you have all the benefits of a handheld scope.

The power bank would remove the common mode noise problem, but the safety aspect has not changed.

Personally I realised I don't have the discipline to avoid ever touching the BNC while probing potentially lethal voltages, so floating is not for me personally.
But I certainly think it is better to make people fully aware of the situation than shout endless warnings without reasons.
Its become like a religion in that way.  Pointless posts about it is dangerous without well articulated reasons or anecdotes about how someone got the shock of their life without explaining in detail why.

[Psi]

You can float your own scope if you want to, but it can be very dangerous unless you fully understand exactly what you're doing.
So it's best to simply tell people to never do it.
Eventually, once they are experienced, they will start to realize how and why it can sometimes be done, and hopefully by then they will have the knowledge to
either
- Do the task a different way that doesn't require floating the scope
Or
- Do it safely.

It's a bad idea to try and explain to a beginner or intermediate skilled person what the risks are and how to do it safely.
To do it safely you really need to understand what you are doing at a fundamental level, not just memorize a list of do's and dont's.

It's like trying to give a newbie a list of do's and dont's to work with a microwave oven transformer.

[tggzzz]

My hakko iron...

I lifted the ground and installed a neon lamp and 40k resistor

So it lights up when im soldering on live circuits.

If you are soldering live circuits, what stops any voltage applied to the tip from causing current to flow through you? What.is the current carrying capacity of a neon bulb?

When soldering sensitive components, what stops any static electricity or induced voltage on the tip topfrom subtlety damaging the components?

In other words, floating a soldering iron is dangerous.

[GnomeZA]

You can float your own scope if you want to, but it can be very dangerous unless you fully understand exactly what you're doing.
So it's best to simply tell people to never do it.

But that is no different from a religious/cult leader telling their believers not to question the religion or cult.
In the world we live in now, with the amount of information and access we have, gatekeeping is pissing in the wind, it does absolutely nothing.
Saying on a public thread that you think the readers may not be as educated as you are <or insert superiority reasons here> is like asking for the Streisand effect to happen.
Some people on that thread WILL be smarter than you (there is always someone smarter or better than you).
By saying that you've solidified in their mind every bad thing they think about you and that they are actually discovering something useful.
I think the best option if you are unable to articulate reasons, is to stay silent, it'll do more to prevent someone from proceeding than gatekeeping.

Sorry bit of a preach but it really is annoying to have to scroll past pointless posts because they distract from the gold nuggets of actual useful information.

And someone will obviously take issue with what I said here so let me ask to that person this:
When last did you accept someone shutting down something you asked with dogma, then walked away from that thinking, now that was some good feedback and so valuable.
Never to think about it again.

[JDW]

Pointless posts about it is dangerous without well articulated reasons or anecdotes about how someone got the shock of their life without explaining in detail why.

Very well... Give us your "well articulated reasons" and "explain in detail why" your position on this topic is vastly superior to all others here.  You have thrashed most people here who are trying to help others by cautioning them, so it's time for you to defend your position about NOT cautioning them.  Otherwise, your dialog on the matter too becomes the very "pointless posts" you preached against.

More specifically, all you've really said is this:

Personally I realised I don't have the discipline to avoid ever touching the BNC while probing potentially lethal voltages, so floating is not for me personally.
But I certainly think it is better to make people fully aware of the situation than shout endless warnings without reasons.

Those two sentences aren't "well articulated reasons" or "explaining in detail" to justify your stance or show us why you have the moral or engineering high ground.

Right now, I see most people here basically telling little kids NOT to play in a busy street or they might get hurt, while you are basically trashing their parents and telling the kids, "it's okay to play in the street, so long as you play it safe."  Yes, it really is basically that.

[tggzzz]

Right now, I see most people here basically telling little kids NOT to play in a busy street or they might get hurt, while you are basically trashing their parents and telling the kids, "it's okay to play in the street, so long as you play it safe."  Yes, it really is basically that.

It is pleasing to see people picking up on the analogy of playing in the road or walking into the road without looking. It is a helpful analogy, since it points out the weakness of the stated position.

In addition to your points I will note that gnomeza is simply wrong to claim "without well articulated reasons or anecdotes". Maybe he can't understand the reasons and specific anecdote mentioned in
https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

It seems he isn't as well-read or clued up as he would like to think.

What's the betting this is sufficiently easy?... Here's the reference to the experienced engineer in Sylvania lighting laboratory: https://groups.io/g/TekScopes/message/10754

[coppercone2]

amazing how much people don't want to buy floating probes LOL

[tggzzz]

Ah, it is good to see that photo I posted long ago being remembered

It does skewer some (other) people's points quite effectively and amusingly.

[madires]

In case that power brick comes with an EMI supression cap between primary and secondary I wouldn't call the DSO floating.

That kind of statement seems to suggest this: "Go ahead and remove the ground from your scopes and then test high voltage because as long as you have an EMI suppression cap between the primary and secondary, it's not floating and therefore A-OK."

Nope! You're reversing cause and effect while adding a thrid thing, which might be even dangerous based on the specific measurement setup.

[Psi]

You can float your own scope if you want to, but it can be very dangerous unless you fully understand exactly what you're doing.
So it's best to simply tell people to never do it.

But that is no different from a religious/cult leader telling their believers not to question the religion or cult.
In the world we live in now, with the amount of information and access we have, gatekeeping is pissing in the wind, it does absolutely nothing.
Saying on a public thread that you think the readers may not be as educated as you are <or insert superiority reasons here> is like asking for the Streisand effect to happen.
Some people on that thread WILL be smarter than you (there is always someone smarter or better than you).
By saying that you've solidified in their mind every bad thing they think about you and that they are actually discovering something useful.
I think the best option if you are unable to articulate reasons, is to stay silent, it'll do more to prevent someone from proceeding than gatekeeping.

Sorry bit of a preach but it really is annoying to have to scroll past pointless posts because they distract from the gold nuggets of actual useful information.

And someone will obviously take issue with what I said here so let me ask to that person this:
When last did you accept someone shutting down something you asked with dogma, then walked away from that thinking, now that was some good feedback and so valuable.
Never to think about it again.

You raise valid points. But it's also valid to choose not to explain dangerous and unnecessary things publicly, and to instead just say "don't do this".
At the end of the day everyone has to live with themselves and the effect they have on the world.
With the wide reach of the internet sometimes posting something will almost definitely lead to someone somewhere trying it and being inured.
The hard part is knowing where the line is.
eg, Does helping 9999 people make up for the fact that 1 person died or was injured while following something you posted online?

[JDW]

In case that power brick comes with an EMI supression cap between primary and secondary I wouldn't call the DSO floating.

That kind of statement seems to suggest this: "Go ahead and remove the ground from your scopes and then test high voltage because as long as you have an EMI suppression cap between the primary and secondary, it's not floating and therefore A-OK."

Nope! You're reversing cause and effect while adding a thrid thing, which might be even dangerous based on the specific measurement setup.

I honestly don't understand what you're talking about.  Let's keep it simple, shall we?  I've said nothing other than things which advocate safety as per the use of a grounded and non-floating scope, for the sake of (1) preventing inadvertent electric shock, and (2) for helping to avoid common mode noise issues on measured waveforms.  It's really that simple.