Electronics > Beginners
My first scope is arriving but my home (old) doesn't have mains grounding
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ogden:

--- Quote from: Fergo on August 08, 2019, 08:50:35 pm ---I will mostly use the scope to probe low voltage such as uC/TTL/Arduino signals and maybe some 12V signals. From what I saw, I should be fine if the DUT is DC or battery powered, but I will mostly use the DUT connected to my computer with USB (as I do a lot of serial stuff), which can provide some risks as the USB negative is theoretically tied to earth (theoretically because my computer is not grounded either, as the sockets don't have the ground pin).

--- End quote ---

In such "low voltage works" case get grounded multi-outlet adapter (splitter) where you plug all your equipment including scope and computer. Obviously you have to avoid any works related to mains voltages.

Fergo:
Thanks for all the suggestions everyone. They've been very insightful (well, with the exception to that plastic bag ground perhaps  ;D).

I am aware that my situation is far from ideal. As a hobbyist, I wanna avoid doing stupid things as I don't have much electrical knowledge, despite messing with electronics for quite some time now (don't even know if that makes any sense...). Anyway, as I mentioned, things should get much better next year, when renovations are planned to start.


--- Quote ---A *LOT* of the problems can be mitigated by equipotential bonding.   Basically you create an equipotential zone where all 'grounds' connect together even that's floating with respect to true ground + the use of a GFCI (RCD in 'europespeak') to trip the mains supply if there is significant leakage current from it.
--- End quote ---

You mean to use something like this 2 prong RCD to plug the equipotential power strip to my mains?
https://www.amazon.com/OAONAN-Replacement-Interrupter-Protection-Conditioner/dp/B073PRH8H3/ref=sr_1_3?keywords=OAONAN+GFCI+Replacement+Plug+Assembly+2-Prongs&qid=1565318806&s=gateway&sr=8-3

I was also giving my situation a little bit more thought and two ideas popped up:

1) I have a 120V UPS 2000VA that is not being used for anything atm. What if I disconnect it from the mains so it becomes active and use it to power the scope and eventually everything that I'd be testing, including the PC and it's USB interface?

2) If I decide to go with the option of using the scope plugged into the mains and have to do some probing on an Arduino connected to a PC via USB: using my notebook while on battery power instead of my desktop computer should be fine, right? Since the device being tested - including it's power source (the notebook) - are isolated.

Again, thank you all for the replies.

KR,
Fergo.


MosherIV:
Hi.

Since your electrical system does not provide Earthing :
None of your equipment will be earthed/grounded no matter what gadget you use/try (only creating an Earth/Ground will work).
You should be able to use the oscilloscope without the fear of accidentally grounding a circuit that is not grounded and damaging YOU or the scope or the circuit.
Any equipment with a metal case is a potential hazard (if a fault causes live mains to touch the case). Fully plastic enclosed equipment is safe(ish).

Just think carefully what you are going to do to the circuit you are measuring with the scope before you start (it is a good habit to form).
Try not to perform measurments on mains electricity while you have no ground.

Stay safe and happy   :-DMM
Electro Detective:
Without knowing how the local utility company implement their Earthing system, sinking a wire into soil, concrete or plumbing fixtures may or may not achieve much,
and or score floating voltage drama.  ???
Maybe the dude next door is playing with electricity too after watching some backyardesque Youtubes   :scared:
perhaps going for it with coat hangers and leaky dumpster grade arc welder that escaped its overdue rendezvous with the metal scrap yard 

AFAIK+EMMV: in a proper Earth/ground system, a UPS in battery backup mode will 'usually' supply 60 volts on both live pins to give 120 volts,
and NO EARTH/ground, unless it sources it from the UPS chassis and or output third pin out of the wall socket.

i.e. even with a UPS in backup mode via battery, you still have a non-Earth referenced floating live electrical system that can still bite you, hopefully via 'inverter to output transformer'
but not with the full force of a power station feeding a street transformer
(but chances are still good for an unplanned demise from the Earth, and consequent burial in it..)

How about a 120v isolation transformer with two 60v secondaries with a center tap between the two acting as the third pin ground-earth reference,
for a 'better than nothing, hey might even work..' portable 'ghetto Earth'?  :-//

NOTE: I will delete the above tip if it's not the 'balanced transformer' set up I was thinking of.

Otherwise, lose the shorts and flip flops,
and enter Float City with gloves, glasses, long sleeves, rubber soles

..and someone nearby with a fully charged phone   ;D

Mechatrommer:

--- Quote from: Electro Detective on August 09, 2019, 10:46:58 am ---Without knowing how the local utility company implement their Earthing system, sinking a wire into soil, concrete or plumbing fixtures may or may not achieve much,
and or score floating voltage drama.  ???

--- End quote ---
electric shock happens when there is current path from contact back to the source. in the case of inside the building, it means the building is acting as conductor to ground and back to wherever the current came from. if no return path, this is just open circuit and contact will float along with the electric potential that is being contacted. another food for thought...
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