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oscilloscope without wire ground

Discussion in 'Electronic Basics' started by Tobias Gadelha, Jul 28, 2013.

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  1. Is there any risk to use oscilloscope without wire ground? Because with wire ground there is a short circuit when I use GND on the line.
     
  2. Tom Biasi

    Tom Biasi Guest

    You shouldn't be touching your ground to line voltage.
     
  3. Em domingo, 28 de julho de 2013 16h16min59s UTC-3, Tom Biasi escreveu:
    but I need measure line (L1) with reference in line(L2).
     
  4. Trick 1:
    Use a dual channel scope with two probes and display the difference.
    This is the regular way to do it.

    Trick 2:
    I have also done the GROUND removal trick,
    but I am an expert in electrocution.
    On my scope I mounted an extra connector to disconnect
    the green/yello wire momentarily.

    better you do Trick one I described above.

    w.
     
  5. Phil Allison

    Phil Allison Guest

    "Tobias Gadelha"

    ** L1 or L2 will be at the almost same potential as ground - so you have no
    real problem.


    ..... Phil
     
  6. Daniel Pitts

    Daniel Pitts Guest

    What makes you sure about that?
     
  7. Daniel Pitts

    Daniel Pitts Guest

    I'm just learning this stuff myself, but I have a question about your
    question... Are you talking about the ground in the plug, or the ground
    for the probe? It would surprise me greatly if they were connected. I
    would *think* that you could connect the probe's GND to a line with any
    potential.
    I would expect only the relative potential to where the other part of
    the oscilloscope is connected need to be within range for the scope, but
    not with reference to the earth.

    I could very will be extremely wrong about all this, but and would love
    to be corrected before I end up passing high voltage through my body ;-)

    Thanks,
    Daniel.
     
  8. Tom Biasi

    Tom Biasi Guest

    Look here: http://www.allaboutcircuits.com/worksheets/scope1.html
    See number 11.
     
  9. Fred Abse

    Fred Abse Guest

    Use a differential probe, or A-B, if your 'scope has the facility.

    NEVER disconnect the supply ground from your instrument. It could be all
    that stands between you and a day out with the undertaker.
     
  10. Phil Allison

    Phil Allison Guest

    "Daniel Pitts"
    ** About what exactly ?

    Make your point or piss off.
     
  11. Daniel Pitts

    Daniel Pitts Guest

    How are you sure that "L1 or L2 will be at the almost same potential as
    ground" is true? I don't understand how you came to that conclusion so I
    was curious how you did.
    My only point was that I wasn't sure, and wondered what your reasoning
    is. No need to get rude.

    My point should have been relatively clear, but I can see it was
    ambiguous with the "so you have no real problem". So, now that I've
    clarified, I'd like a real answer. Unless you've realized you were
    wrong, then a simple note to that effect would also be polite.

    Thanks,
    Daniel.
     
  12. Daniel Pitts

    Daniel Pitts Guest

    I see... That makes sense, but is still surprising to me. So it seems
    likely depending on the OPs application, coupling transformers may be a
    safer way to handle this situation. Thanks for the lesson ;-)
     
  13. Phil Allison

    Phil Allison Guest

    "Daniel Pitts"
    ** The codes L1 and L2 are very often seen on schematics refering to the
    active and neutral conductors.

    ( Nothing suggested the OP was dealing with 3 phase power and I hope to
    hell he is not)

    Neutral conductors are always linked to ground at the service box.

    So, the voltage seen from active to ground is almost the same as that from
    to active to neutral - the only difference being due to current in the
    particular neutral wire due to some load.

    Get your DMM out and check it sometime.



    .... Phil
     
  14. Tom Biasi

    Tom Biasi Guest

    In the USA neutral and ground are "usually" connected at the service box
    but not always. L1 and L2 are usually hot wires wrt ground.
    Confusion with terminology is dangerous. This is a basic group.

    Tom
     
  15. Daniel Pitts

    Daniel Pitts Guest

    I was not aware of that convention. Thanks.
     
  16. Phil Allison

    Phil Allison Guest

    "Tom Biasi"
    ** It must be connected to ground somewhere - or else it is simply NOT a
    neutral.


    ** Only IF you are speaking about two phase AC supply wiring in the USA.

    AFAIK - something only used for large appliances like stoves and water
    heaters.

    Not electronics.

    ** You are a very basic person.

    FYI.

    Maybe the OP was posting from the USA and WAS referring to two phase,
    240V power.

    But he made no mention of either.

    Google Groups posters are always PITA about crucial details like this.



    ..... Phil
     
  17. Tom Biasi

    Tom Biasi Guest

    Daniel,
    Scopes have the outer shield connector attached to the BNC conector. The
    outer connector of the BNC is common with the chassis of the scope. So
    the alligator clip on the scope is the same as chassis ground on the scope.
    In the USA one of the line wires is hot and the other is neutral. In
    most cases the neutral and ground are the same, but not always. In some
    220 volt countries both L1 and L2 are hot to ground.
    It would serve you to consider the clip on the scope a chassis and earth
    ground. Anywhere you touch it is like touching ground there.

    Tom
     
  18. Tom Biasi

    Tom Biasi Guest

    Neutral and ground are not always the same.
    Thank you. I try.
     
  19. Phil Allison

    Phil Allison Guest

    "Tom Biasi"

    ** Of course they are not the SAME !!!!!!!

    Neutrals ARE current carrying conductors.

    Safety grounds are NOT, until a fault condition arises.

    Make your point clear.



    .... Phil
     
  20. Em terça-feira, 30 de julho de 2013 02h01min58s UTC-3, Phil Allison escreveu:
    Phil

    I'm from Brazil and here N= Neutral ; L1 =220V (-120º); L2=220V (0º) and L3(+120º) therefore L1 in oscilloscope will be GND and L2 the prove.
    Is it possible with the wire groud conected in the jack.
     
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