# oscilloscope without wire ground

T

Jan 1, 1970
0
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.

T

#### Tom Biasi

Jan 1, 1970
0
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.
You shouldn't be touching your ground to line voltage.

T

Jan 1, 1970
0
Em domingo, 28 de julho de 2013 16h16min59s UTC-3, Tom Biasi escreveu:
You shouldn't be touching your ground to line voltage.

but I need measure line (L1) with reference in line(L2).

H

#### Helmut Wabnig

Jan 1, 1970
0
Em domingo, 28 de julho de 2013 16h16min59s UTC-3, Tom Biasi escreveu:

but I need measure line (L1) with reference in line(L2).

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.

P

#### Phil Allison

Jan 1, 1970
0
but I need measure line (L1) with reference in line(L2).

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

..... Phil

D

#### Daniel Pitts

Jan 1, 1970
0

** L1 or L2 will be at the almost same potential as ground - so you have no
real problem.
What makes you sure about that?

D

#### Daniel Pitts

Jan 1, 1970
0
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.

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.

T

#### Tom Biasi

Jan 1, 1970
0
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.

See number 11.

F

#### Fred Abse

Jan 1, 1970
0
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.

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.

P

#### Phil Allison

Jan 1, 1970
0
"Daniel Pitts"
Phil said:

What makes you sure about that?

Make your point or piss off.

D

#### Daniel Pitts

Jan 1, 1970
0
"Daniel Pitts"

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.
Make your point or piss off.
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.

P

#### Phil Allison

Jan 1, 1970
0
"Daniel Pitts"
Phil said:
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.

** 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

T

#### Tom Biasi

Jan 1, 1970
0
"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
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

D

#### Daniel Pitts

Jan 1, 1970
0
"Daniel Pitts"

** The codes L1 and L2 are very often seen on schematics refering to the
active and neutral conductors.
I was not aware of that convention. Thanks.

P

#### Phil Allison

Jan 1, 1970
0
"Tom Biasi"
In the USA neutral and ground are "usually" connected at the service box
but not always.

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

L1 and L2 are usually hot wires wrt ground.

** 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.

Confusion with terminology is dangerous.
This is a basic group.

** 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.

..... Phil

T

#### Tom Biasi

Jan 1, 1970
0
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 ;-)

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

T

#### Tom Biasi

Jan 1, 1970
0
"Tom Biasi"

** It must be connected to ground somewhere - or else it is simply NOT a
neutral.
Neutral and ground are not always the same.
** 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.

Thank you. I try.

P

#### Phil Allison

Jan 1, 1970
0
"Tom Biasi"
Neutral and ground are not always the same.

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

Neutrals ARE current carrying conductors.

Safety grounds are NOT, until a fault condition arises.

.... Phil

T

Jan 1, 1970
0
Em terça-feira, 30 de julho de 2013 02h01min58s UTC-3, Phil Allison escreveu:
"Tom Biasi"

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

Neutrals ARE current carrying conductors.

Safety grounds are NOT, until a fault condition arises.

... Phil

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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