oscilloscope without wire ground

[Phil Allison]

"Tom Biasi"

Phil Allison wrote:

** 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.


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.

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



..... Phil

 

[Tom Biasi]

On 7/29/2013 9:58 PM, Daniel Pitts wrote:

On 7/29/13 11:41 AM, Tom Biasi wrote:
On 7/29/2013 12:23 PM, Daniel Pitts wrote:
On 7/28/13 11:49 AM, Tobias Gadelha wrote:
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.

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


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

 

[Tom Biasi]

On 7/30/2013 12:32 AM, Phil Allison wrote:

"Tom Biasi"
Phil Allison wrote:

** 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.


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.
Neutral and ground are not always the same.


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.

Thank you. I try.

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.
Agreed.



.... Phil

 

[Phil Allison]

"Tom Biasi"

Phil Allison wrote:

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


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.

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.

Make your point clear.



.... Phil

 

[Tobias Gadelha]

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

"Tom Biasi"

Phil Allison wrote:



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





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.



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.



Make your point clear.







... Phil

Phil

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

 

[Tobias Gadelha]

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

"Tom Biasi"

Phil Allison wrote:



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





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.



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.



Make your point clear.







... Phil

Phil

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

 

[Michael A. Terrell]

Phil Allison wrote:

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.

His IP address resolves to Brazil.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

 

[Phil Allison]

"Tobias Gadelha"

I'm from Brazil and here N= Neutral ; L1 =220V (-120ş); L2=220V (0ş) and
L3(+120ş) therefore L1 in oscilloscope will be GND and L2 the prove.


** My god, the fool IS mucking about with 3 phase power !


Is it possible with the wire groud conected in the jack.


** Question time:

Have you got a dual trace /channel scope with "invert" function on one
channel ?

Do you have two 10:1 probes ?

If so, others have given you the answer already.

BTW:

3 phase power is VERY DANGEROUS !!!

Beginners should NOT be touching it.



.... Phil

 

[Tom Biasi]

On 7/30/2013 1:01 AM, Phil Allison wrote:

"Tom Biasi"
Phil Allison wrote:

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


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.

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.

Make your point clear.



... Phil




I made my point clear Phil.

You said, "Neutral conductors are always linked to ground at the service
box."

I said," In the USA neutral and ground are "usually" connected at the
service box but not always."

That's clear enough.
No need to go beyond that.

Tom

 

[Phil Allison]

"Tom Biasi"

Phil Allison wrote:
"Tom Biasi"
Phil Allison wrote:

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


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.

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.

Make your point clear.



I made my point clear Phil.

** Clear as mud - pal.

You said, "Neutral conductors are always linked to ground at the service
box."

I said," In the USA neutral and ground are "usually" connected at the
service box but not always."

That's clear enough.

** NO it is NOT !!!!!!!!!

No need to go beyond that.

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

Ever see the movie "Groundhog Day" ??


.... Phil

 

[Ian Field]

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:b5remlFcru3U1@mid.individual.net...

"Tobias Gadelha"

I'm from Brazil and here N= Neutral ; L1 =220V (-120ş); L2=220V (0ş) and
L3(+120ş) therefore L1 in oscilloscope will be GND and L2 the prove.


** My god, the fool IS mucking about with 3 phase power !

Persuade him to set up a live feed webcam while I go get deckchair &
popcorn.

 

[Ian Field]

"Daniel Pitts" <newsgroup.nospam@virtualinfinity.net> wrote in message
news:2BGJt.301813$hK5.205179@fx15.iad...

On 7/29/13 7:23 PM, Phil Allison wrote:
"Daniel Pitts"
Phil Allison wrote:
"Daniel Pitts"
Phil Allison wrote:
"Tobias Gadelha"

You shouldn't be touching your ground to line voltage.

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.

What makes you sure about that?

** About what exactly ?

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.
I was not aware of that convention. Thanks.

IWHT in that case L1 & L2 mean "line 1" & "line 2" - not live.

If "L" refers to live - there's probably a 3rd one lurking somwhere!

 

[Ian Field]

"Fred Abse" <excretatauris@invalid.invalid> wrote in message
newsan.2013.07.28.20.10.00.516740@invalid.invalid...

On Sun, 28 Jul 2013 11:49:54 -0700, Tobias Gadelha wrote:

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.

I used to do it a lot in the 80's when most TVs had bridge-rectifier mains
in, and chassis pulsing at -320V.

In some the 'SMPSU' was as basic as a SCR masquerading as a buck regulator -
they used a bridge-rectifier input (with its live chassis) to get 100Hz
pulses so they could use a smaller inductor.

Can't deny it bit me a few times!

 

[Tobias Gadelha]

Em domingo, 28 de julho de 2013 15h49min54s UTC-3, Tobias Gadelha escreveu:

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.

ok people, resolved. thanks