Is Switch-Mode Power Supply Connected to Power Strip Connected to Earth Ground?

[Roseblade23]

Hello everyone!

I'm new to electronics, and just purchased an oscilloscope. To ensure that I don't blow anything up, I'm researching as much as I can before using it.

I'm using this switch-mode power supply to power a breadboard DC circuit (Ben Eater's 8-Bit CPU), which I usually keep plugged into a power strip:

https://www.jameco.com/z/EPAS-101W-05-CUI-5V-2A-10W-AC-DC-Switching-Wall-Adapter_2188537.html

I've watched Dave's video "#279 How NOT To Blow Up Your Oscilloscope!" a couple times, and it sounds like I'm still connected to Earth Ground by doing this (plugging the SMPS into a power strip)? The power strip has the standard 3 pins. Which would be bad? Or, because the SMPS only has two prongs, I'm protected from connecting to ground through it?

I got a little confused, when at 8:05 he said we're okay as long as the SMPS has no Earth connection at all.
https://youtu.be/xaELqAo4kkQ?t=433

Thanks for any help!

[perdrix]

OK It's really not too hard.  If the Device Under Test (DUT) which in this case is an SMPS, has no earth connection, then it is safe to connect a 'scope probe attached to an earthed 'scope across any two points in the circuit as the one attached to the probe ground will "float" to the 'scope's earth potential.

Notes:
 
 1) This doesn't mean it's safe to prod your fingers in there - even if only one - you could at best get a nasty burn if your finger touched two points of different voltage, and at worst if you had two fingers in there you could kill yourself.

 2) Don't connect two probe earth leads to points in the DUT with differing potential.

David

[Roseblade23]

Hey there,

I understood about a device not having an earth connection being safe, but my concern was that I wasn't sure if my SMPS had an earth connection or not, since it was plugged into a power strip that did have an earth connection.

In doing more research and asking on Reddit as well, I've learned that if the power supply has the double square symbol on its label, it means it's a Class II double insulated supply using flyback technology, and is mains earth isolated. Also, the SMPS having two prongs with no ground pin is not sufficient to determine that it is isolated (although the vast majority of the time it is) -- in North America the neutral conductor of the wall outlet is connected to mains earth at the breaker panel. So you would still be connected to earth ground if this symbol wasn't on the device.

Thanks!

[JustMeHere]

Do a continuity test from the AC inputs to the DC outputs.  If you get no buzz then it is isolated.  Most are isolated.   (Unplug everything first.  And make sure the supply has discharged it's caps first.)