(Howard Knight) writes:
I get the shock when I touch any part of the back of my computer or
wires, and also touch the metal part of the cable that comes in and
connects to my cable modem. Here's the deal:

I live in an older house that is not grounded. The ground prong on
the outlets isn't connected to ground or anything else.

Red flag. This is problem #1. This isn't a ground loop. This is an
absence of ground. The former is an inconvenience, the latter can
kill ya.

Also, I've determined that the coax cable coming in to my cable
modem is grounded.

Typically staked at the junction box by the cable company.

Somthing seems to be making the ground prong on my outlet hot. I've
narrowed down the problem to my power strip. I've unplugged
everything from my outlet and I check the outlet for voltage.
Neutral to hot gives me 110V. Neutral to ground give me nothing
(actually, for some odd reason, there does seem to be a slight
voltage (less than 2V).

The odd reason is that if we believe what you're telling us (i.e. that
your ground on your outlet is completely floating) I'd believe any
voltage you'd tell me between ground and the neutral of the outlet.

Hot to ground also gives me nothing. As one would expect.

As one would expect in Danger World where ground is left completely
floating. :-)

In the Safe World, neutral and ground should be the same potential
with 0V, and hot to ground should measure in the 110-120V range.

Now, if I plug in a power strip and do the same check on one of the
outlets on the power strip, I get: neutral to hot 110V,

Good.

Neutral to ground around 60V

Wee! This is a Big Problem.

and hot to ground around 60V. Is this right?

Oy. No.

You gotta remember here, your ground in your outlets is completely
floating, and someone should tell you this is Very Bad.

I've checked this with two power strips and I get the same results.
What would cause this? Is the polarity on my outlet wrong? Or, am
I just a dummy and am misintepreting what is going on. This
misterious 60V is what give me the shock.

Call an electrician. Today. You've got potentially lethal problems
with your home's electric wiring. You may also have some power
strips in need of replacement.

60V on your third wire ground is Not Good (tm). Since your computer
is a metal enclosed 3-wire appliance, it's presenting allcomers with
60V ready to shock the crap out of em.

Most aren't aware that surge suppressing power strips do nothing
without a real third wire ground, and it appears that they might also
be creating a rather hazardous situation. I suspect that these may be
surge suppressing power strips with some circuitry that is potentially
faulty (burned out MOV's for instance) and is therefore creating a
more hazardous situation than you have at your outlet to begin with
because your outlet is heinously miswired.

Don't take offense, but do call an electrician.

Best Regards,
--
/"\ ASCII Ribbon Campaign | Todd H
\ / | http://www.toddh.net/
X Promoting good netiquette | http://triplethreatband.com/
/ \ http://www.toddh.net/netiquette/ | "4 lines suffice."

First, let me tell you that I'm a retard when it comes to electronic
stuff. Anyway...

I was fiddling around behind my computer and got a nice shock. I'm
trying to figure out this problem and am hoping you folks could
help me out.

I get the shock when I touch any part of the back of my computer or
wires, and also touch the metal part of the cable that comes in and
connects to my cable modem. Here's the deal:

I live in an older house that is not grounded. The ground prong on
the outlets isn't connected to ground or anything else. Also, I've
determined that the coax cable coming in to my cable modem is
grounded. Somthing seems to be making the ground prong on my outlet
hot. I've narrowed down the problem to my power strip. I've
unplugged everything from my outlet and I check the outlet for
voltage. Neutral to hot gives me 110V. Neutral to ground give me
nothing (actually, for some odd reason, there does seem to be a
slight voltage (less than 2V). Hot to ground also gives me nothing.
As one would expect.

Now, if I plug in a power strip and do the same check on one of the
outlets on the power strip, I get: neutral to hot 110V, neutral to
ground around 60V and hot to ground around 60V. Is this right?
I've checked this with two power strips and I get the same results.
What would cause this? Is the polarity on my outlet wrong? Or,
am I just a dummy and am misintepreting what is going on. This
misterious 60V is what give me the shock.

Howard

Todd H. ) wrote:
: ...your outlet is heinously miswired.

Not miswired, just wired 40+ years ago with no ground. Couldn't I
just ground the outlet myself? Run a wire from the ground in the
outlet to a water pipe outside? Would that solve my problems?

Howard

Howard Knight wrote:
Todd H. ) wrote:
: ...your outlet is heinously miswired.

Not miswired, just wired 40+ years ago with no ground. Couldn't I
just ground the outlet myself? Run a wire from the ground in the
outlet to a water pipe outside? Would that solve my problems?

Howard

There are electrical codes with which you should comply.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

Howard Knight wrote:
Todd H. ) wrote:
: ...your outlet is heinously miswired.

Not miswired, just wired 40+ years ago with no ground. Couldn't I
just ground the outlet myself? Run a wire from the ground in the
outlet to a water pipe outside? Would that solve my problems?

Howard,
First, I think you should replace that outlet strip. They have MOV's
between the hot and ground and neutral and ground. When an MOV gets a
big surge, they start leaking current that they would have blocked
before the damage. Because your ground is floating, the leakage of the
two sets of MOV's has made a voltage divider between hot and neutral
with the ground at the midpoint. Grounding the outlet feeding your
computer is a good idea, but it may trip breakers or blow fuses if the
outlet strip is really hammered.

You might think about getting your house wiring brought up to modern
configuration, proper grounding and GFI outlets add a lot to the
electrical safety of a house. It would probably add to the resale value
as well. If you are in a rental house, good luck.

Bob

On Fri, 10 Jun 2005 21:39:09 +0000, Howard Knight wrote:

First, let me tell you that I'm a retard when it comes to electronic
stuff. Anyway...

I was fiddling around behind my computer and got a nice shock. I'm
trying to figure out this problem and am hoping you folks could
help me out.

I get the shock when I touch any part of the back of my computer or
wires, and also touch the metal part of the cable that comes in and
connects to my cable modem. Here's the deal:

I live in an older house that is not grounded. The ground prong on
the outlets isn't connected to ground or anything else.

Then get that fixed by a qualified professional before you burn
your house down or kill one of your children.

Sorry,
Rich

On Fri, 10 Jun 2005 23:31:57 +0000, Howard Knight wrote:

Todd H. ) wrote:
: ...your outlet is heinously miswired.

Not miswired, just wired 40+ years ago with no ground. Couldn't I
just ground the outlet myself? Run a wire from the ground in the
outlet to a water pipe outside? Would that solve my problems?

Use #10 AWG solid bare copper, and if you can't afford to have it
done by a qualified professional, at least have it inspected by
a qualified professional.

Don't murder your children.

Good Luck!
Rich

On Fri, 10 Jun 2005 21:39:09 -0000,
(Howard Knight) wrote:

First, let me tell you that I'm a retard when it comes to electronic
stuff. Anyway...

I was fiddling around behind my computer and got a nice shock. I'm
trying to figure out this problem and am hoping you folks could
help me out.

I get the shock when I touch any part of the back of my computer or
wires, and also touch the metal part of the cable that comes in and
connects to my cable modem. Here's the deal:

I live in an older house that is not grounded. The ground prong on
the outlets isn't connected to ground or anything else. Also, I've
determined that the coax cable coming in to my cable modem is
grounded. Somthing seems to be making the ground prong on my outlet
hot. I've narrowed down the problem to my power strip. I've
unplugged everything from my outlet and I check the outlet for
voltage. Neutral to hot gives me 110V. Neutral to ground give me
nothing (actually, for some odd reason, there does seem to be a
slight voltage (less than 2V). Hot to ground also gives me nothing.
As one would expect.

Now, if I plug in a power strip and do the same check on one of the
outlets on the power strip, I get: neutral to hot 110V, neutral to
ground around 60V and hot to ground around 60V. Is this right?
I've checked this with two power strips and I get the same results.
What would cause this? Is the polarity on my outlet wrong? Or,
am I just a dummy and am misintepreting what is going on. This
misterious 60V is what give me the shock.

Howard

The doom and gloomers sure do come out of the woodwork.
There is probably nothing at all wrong with your power strips. If they
have surge protective devices in them what you are reading may be
normal. Some power strips have capacitors from hot to ground and
neutral to ground in addition to mov's. Mov's by themselves have some
capacitance and can act like a voltage divider as one poster
mentioned. The fact that you measure 60 volts would indicate that both
devices are acting in the same manor and dividing the voltage equally,
so they are probably ok. However because of the nature of the devices
it puts some voltage on your items that are tied to the ground of the
power strip.

You should run a ground wire from the ground pin on the outlet back to
the power service panel (breaker/fuse panel). The service panel should
have a ground wire going to a ground rod already.

Running your outlet ground wire to a ground of its own would be better
than nothing but the correct way to do it is to run it right to your
service panel.

Regards
Gary K4FMX

On Fri, 10 Jun 2005 21:21:55 -0400 Gary Schafer
wrote:

The doom and gloomers sure do come out of the woodwork.

Yep, I completely agree. It's rather clear that no one before Gary had
much of a clue as to what was really going on here.

What you are seeing is the completely normal result of having a home
system with no ground, a power strip with surge protection, and a
voltmeter with a high imput impedance.

You can leave things just the way they are, but the best thing would
be to update the house wiring and give yourself some good grounds. In
the meantime, your surge protector only gives your computer limited
protection.

A proper ground is applied at the service entrance (where the AC power
enters the house) and follows the wiring out to each outlet from
there. An alternate ground can still protect you from electrical shock
if it is well done, but it may cause other problems and may not allow
your surge limiters to protect your equipment as well.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

Rather scary that so many know so much as to reply ...
without first learning electrical basics.

The wall receptacle safety ground must have a dedicated wire
connection to breaker box safety ground. Not to earth; to
safety ground. And definitely not a connection to pipes.

Wire connection to pipes must be to remove electricity from
that pipe. Never make a connection intended to dump
electricity into pipes. A worst case scenario, a pipe
connection might only electrify a wet human in a shower or
bath. Wet is the worst time to touch electricity.

Connection to earth ground also does nothing useful. The
important connection to earth must be from breaker box only.
A receptacle safety ground must connect to breaker box so that
a wiring fault does trip the circuit breaker. No way around
that grounding (bonding) requirement.

The wall receptacle, power strip, or computer need not be
miswired to obtain leakage voltage. Without a safety ground,
then leakage currents might cause the chassis to 'feel'
electrically hot. Not a danger to a dry human. However
leakage can cause damage to interconnected computer components
and cause other irritating problems.

Easiest solution is to have an electrician route a properly
earthed wire to that receptacle. Electricians have fancy toys
that make 'impossible to route' wires simple.

If a receptacle is not safety grounded, then the circuit
should be GFCIed. GFCI is a minimum necessary correction.

Better power strip is typically about $3+, no nonsense surge
protector or filter components inside, AND the power strip
must include a 15 amp circuit breaker. The breaker being
important for human safety - for reasons not discussed here.

Howard Knight wrote:
Todd H. ) wrote:
: ...your outlet is heinously miswired.

Not miswired, just wired 40+ years ago with no ground. Couldn't I
just ground the outlet myself? Run a wire from the ground in the
outlet to a water pipe outside? Would that solve my problems?

Howard

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
? "Todd H." ?????? ??? ??????
...
(Howard Knight) writes:
I get the shock when I touch any part of the back of my computer or
wires, and also touch the metal part of the cable that comes in and
connects to my cable modem. Here's the deal:

I live in an older house that is not grounded. The ground prong on
the outlets isn't connected to ground or anything else.

Red flag. This is problem #1. This isn't a ground loop. This is an
absence of ground. The former is an inconvenience, the latter can
kill ya.

Is this legal in USA?Here, there are people who put shucko-plugs in old
fashioned three-prong receptacles, with the result, abcence of ground (the
appliance works, but is not grounded).Modern computers that work in the GHz
range need very good grounding, because their case becomes hot otherwise
from induced high-frequency currents.
Also, I've determined that the coax cable coming in to my cable
modem is grounded.

Typically staked at the junction box by the cable company.

Somthing seems to be making the ground prong on my outlet hot. I've
narrowed down the problem to my power strip. I've unplugged
everything from my outlet and I check the outlet for voltage.
Neutral to hot gives me 110V. Neutral to ground give me nothing
(actually, for some odd reason, there does seem to be a slight
voltage (less than 2V).

The odd reason is that if we believe what you're telling us (i.e. that
your ground on your outlet is completely floating) I'd believe any
voltage you'd tell me between ground and the neutral of the outlet.

In my house:hot to neutral and hot to ground 225 volts (3:10 pm)and, of
course, neutral to ground 0 volts.I have checked every inch of the
installation myself, because I think that electricity is quite a good
friend,but canbecome dangerous sometimes.
Hot to ground also gives me nothing. As one would expect.

As one would expect in Danger World where ground is left completely
floating. :-)

In the Safe World, neutral and ground should be the same potential
with 0V, and hot to ground should measure in the 110-120V range.

Notice however that neutral even having a potential of 0 volts is run by
large enough currents to cause problems in bad installations (neutral bars
in distribution panels and neutrals in electric ranges e.g. tend to burn to
be charcoaled completely).
Now, if I plug in a power strip and do the same check on one of the
outlets on the power strip, I get: neutral to hot 110V,

Good.

Neutral to ground around 60V

Wee! This is a Big Problem.

and hot to ground around 60V. Is this right?

Oy. No.

You gotta remember here, your ground in your outlets is completely
floating, and someone should tell you this is Very Bad.

I've checked this with two power strips and I get the same results.
What would cause this? Is the polarity on my outlet wrong? Or, am
I just a dummy and am misintepreting what is going on. This
misterious 60V is what give me the shock.

Call an electrician. Today. You've got potentially lethal problems
with your home's electric wiring. You may also have some power
strips in need of replacement.

60V on your third wire ground is Not Good (tm). Since your computer
is a metal enclosed 3-wire appliance, it's presenting allcomers with
60V ready to shock the crap out of em.

Most aren't aware that surge suppressing power strips do nothing
without a real third wire ground, and it appears that they might also
be creating a rather hazardous situation. I suspect that these may be
surge suppressing power strips with some circuitry that is potentially
faulty (burned out MOV's for instance) and is therefore creating a
more hazardous situation than you have at your outlet to begin with
because your outlet is heinously miswired.

Don't take offense, but do call an electrician.

Best Regards,
--
/"\ ASCII Ribbon Campaign | Todd H
\ / | http://www.toddh.net/
X Promoting good netiquette | http://triplethreatband.com/
/ \ http://www.toddh.net/netiquette/ | "4 lines suffice."

Dimitrios Tzortzakakis wrote:

Is this legal in USA?Here, there are people who put shucko-plugs in old
fashioned three-prong receptacles, with the result, abcence of ground (the
appliance works, but is not grounded).Modern computers that work in the GHz
range need very good grounding, because their case becomes hot otherwise
from induced high-frequency currents.


Bull****. The potential at the case is power leaked in the psu, not
_any_ other parts in the computer. The psu has a filter on the input,
which leaks tiny currents to ground/chassis. This has nothing to do with
the cpu or any other thing. It has nothing to do with induction afaik.


--
MVH,
Vidar

www.bitsex.net

"Howard Knight" wrote in message
...
I live in an older house that is not grounded. The ground prong on
the outlets isn't connected to ground or anything else.

if you want to carry on living i sugest you get this problem rectified
imediatly. if you were living in the UK the wiring would be condemed by the
power company as soon as they were aware of it.

Colin.

Jim Adney wrote:
On Fri, 10 Jun 2005 21:21:55 -0400 Gary Schafer
wrote:


The doom and gloomers sure do come out of the woodwork.


Yep, I completely agree. It's rather clear that no one before Gary had
much of a clue as to what was really going on here.

What you are seeing is the completely normal result of having a home
system with no ground, a power strip with surge protection, and a
voltmeter with a high imput impedance.

But ... that combination can be deadly. If you don't believe me,
google "guitar amp death caps."


You can leave things just the way they are, but the best thing would
be to update the house wiring and give yourself some good grounds. In
the meantime, your surge protector only gives your computer limited
protection.

A proper ground is applied at the service entrance (where the AC power
enters the house) and follows the wiring out to each outlet from
there. An alternate ground can still protect you from electrical shock
if it is well done, but it may cause other problems and may not allow
your surge limiters to protect your equipment as well.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------


--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

w_tom wrote:

Rather scary that so many know so much as to reply ...
without first learning electrical basics.

Oh, gawd. He's invaded yet another group.

On Fri, 10 Jun 2005 23:51:39 -0500, Jim Adney
wrote:

It's rather clear that no one before Gary had
much of a clue as to what was really going on here...

You can leave things just the way they are....

Speaking of clues: if the OP leaves things "just the way they are," he
will have an ever-present and very real 60V potential between his
computer case and the cable shield. That's 60Vrms at 60Hz between
bare, exposed metal conductors possibly just inches apart. Dunno
about you, but I wouldn't want that.

On Sat, 11 Jun 2005 12:31:18 -0700, Al Brenan
wrote:


It's rather clear that no one before Gary had
much of a clue as to what was really going on here...
You can leave things just the way they are....

Speaking of clues: if the OP leaves things "just the way they are,"
he will have an ever-present and very real 60V potential between his
computer case and the cable shield. That's 60Vrms at 60Hz between
bare, exposed metal conductors possibly just inches apart. Dunno
about you, but I wouldn't want that.


http://users.tkk.fi/~then/mytexts/ungrounded_pc.html

On Fri, 10 Jun 2005 23:31:57 -0000,
(Howard Knight) wrote:

Todd H. ) wrote:
: ...your outlet is heinously miswired.

Not miswired, just wired 40+ years ago with no ground. Couldn't I
just ground the outlet myself? Run a wire from the ground in the
outlet to a water pipe outside? Would that solve my problems?

Howard
If you have a un-grounded U-Ground outlet installed in a 2 wire
UN-GROUNDED box, this is a violation of most US electrical codes.
You need to replace 2 prong outlets wit 2 prong outlets UNLESS there
is a ground wire attached to the 1)box, 2)the green terminal on the
outlet.

Many bathroom outlet and light fixture boxes were required to have a
separate (bare) ground wire connected to the cold water piping. This
is fine until the addition of Di-electric union or plastic piping from
the water supply. If your electric service does not have a ground rod
driven into the earth, have this added to the required cold water
ground bond wire at the service entrance.

, _
, | \ MKA: Steve Urbach
, | )erek No JUNK in my email please
, ____|_/ragonsclaw
, / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org

On Sat, 11 Jun 2005 02:43:59 -0400, w_tom wrote:

The wall receptacle safety ground must have a dedicated wire
connection to breaker box safety ground. Not to earth; to
safety ground. And definitely not a connection to pipes.
MODERN rules. Old rules DID require COLD WATER PIPES, but *never* GAS
pipes.

, _
, | \ MKA: Steve Urbach
, | )erek No JUNK in my email please
, ____|_/ragonsclaw
, / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org

Vidar Løkken wrote:

Bull****. The potential at the case is power leaked in the psu, not
_any_ other parts in the computer. The psu has a filter on the input,
which leaks tiny currents to ground/chassis. This has nothing to do with
the cpu or any other thing. It has nothing to do with induction afaik.




Just for fun I measured those values on a atx psu connected to a 100W
load, trough a insulation xfmr. I measured 60-65V, and 70µA. This
current is so tiny you won't normally feel it, so no danger to human
beings. However, if some equipment is earthed, and some not, it might
destroy electronics.
Also note that this was in a 220V IT circuit, which means that earth is
nominally floating.

--
MVH,
Vidar

www.bitsex.net

Jim Adney writes:
On Fri, 10 Jun 2005 21:21:55 -0400 Gary Schafer
wrote:

The doom and gloomers sure do come out of the woodwork.

Yep, I completely agree. It's rather clear that no one before Gary had
much of a clue as to what was really going on here.

What you are seeing is the completely normal result of having a home
system with no ground, a power strip with surge protection, and a
voltmeter with a high imput impedance.

You can leave things just the way they are,

.....if of course one enjoys the safety and thrill of getting shocked
by your computer case. :-) The situation may be relatively common, but
it's far from normal or safe.

The only responsible solution to the OP's quandry is an electrician,
plain and simple.

Then again, what would I know about electricity?

Best Regards,
--
/"\ ASCII Ribbon Campaign | Todd H
\ / | http://www.toddh.net/
X Promoting good netiquette | http://triplethreatband.com/
/ \ http://www.toddh.net/netiquette/ | "4 lines suffice."

Vidar Løkken wrote:
Vidar Løkken wrote:

Bull****. The potential at the case is power leaked in the psu, not
_any_ other parts in the computer. The psu has a filter on the input,
which leaks tiny currents to ground/chassis. This has nothing to do
with the cpu or any other thing. It has nothing to do with induction
afaik.




Just for fun I measured those values on a atx psu connected to a 100W
load, trough a insulation xfmr. I measured 60-65V, and 70µA. This
current is so tiny you won't normally feel it, so no danger to human
beings.

You might be shocked (pun intended) to learn that capacitors (and other
components) sometimes fail.

However, if some equipment is earthed, and some not, it might
destroy electronics.
Also note that this was in a 220V IT circuit, which means that earth is
nominally floating.



--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

On Sat, 11 Jun 2005 12:31:18 -0700 Al Brenan
wrote:

On Fri, 10 Jun 2005 23:51:39 -0500, Jim Adney
wrote:

It's rather clear that no one before Gary had
much of a clue as to what was really going on here...

You can leave things just the way they are....

Speaking of clues: if the OP leaves things "just the way they are," he
will have an ever-present and very real 60V potential between his
computer case and the cable shield. That's 60Vrms at 60Hz between
bare, exposed metal conductors possibly just inches apart. Dunno
about you, but I wouldn't want that.

Sure, it's 60V as seen on a 10 MOhm meter, but the source impedance is
on the order of a MegOhm. That's never going to provide enough current
to be dangerous. Of course that assumes that all his components remain
in good condition. If something actually fails, then you're right and
he is without a safety ground.

He could experiment with this by touching both "grounds" at the same
time and measuring the voltage on his PC chassis at the same time.
He'll discover that he has grounded the PC and that there is no longer
a voltage there.

He's already explained that he gets a shock whenever he touches both
parts. I believe him. The fact that he's done this several times with
no extreme effects implies that it's a perceptable amount of current,
but not a dangerous one. This is what one would expect from a power
strip with surge protection that lacked a ground.

He could probably improve his situation by just grounding his PC to
the cable shield. This carries the possiblity of passing a shock on to
someone working on the cable system, however, so that's why I really
don't recommend it.

And I agree, we would ALL be better off with all grounded outlets, but
there are many old houses around which just don't have them.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

If that happens, then why does not my GFCI breaker trip?

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
? "Vidar Løkken" ?????? ??? ??????
...
Dimitrios Tzortzakakis wrote:

Is this legal in USA?Here, there are people who put shucko-plugs in old
fashioned three-prong receptacles, with the result, abcence of ground
(the
appliance works, but is not grounded).Modern computers that work in the
GHz
range need very good grounding, because their case becomes hot otherwise
from induced high-frequency currents.


Bull****. The potential at the case is power leaked in the psu, not
_any_ other parts in the computer. The psu has a filter on the input,
which leaks tiny currents to ground/chassis. This has nothing to do with
the cpu or any other thing. It has nothing to do with induction afaik.


--
MVH,
Vidar

www.bitsex.net

Then why is a computer in a fully enclosure metal case?Provided, that a
computer works with voltages not higher than 12 volt, and the PSU is already
shielded, why not put it in a plastic case?

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
? "Vidar Løkken" ?????? ??? ??????
...
Vidar Løkken wrote:

Bull****. The potential at the case is power leaked in the psu, not
_any_ other parts in the computer. The psu has a filter on the input,
which leaks tiny currents to ground/chassis. This has nothing to do with
the cpu or any other thing. It has nothing to do with induction afaik.




Just for fun I measured those values on a atx psu connected to a 100W
load, trough a insulation xfmr. I measured 60-65V, and 70µA. This
current is so tiny you won't normally feel it, so no danger to human
beings. However, if some equipment is earthed, and some not, it might
destroy electronics.
Also note that this was in a 220V IT circuit, which means that earth is
nominally floating.

--
MVH,
Vidar

www.bitsex.net

Vidar Løkken wrote:
Vidar Løkken wrote:

Bull****. The potential at the case is power leaked in
the psu, not
_any_ other parts in the computer. The psu has a filter
on the input,
which leaks tiny currents to ground/chassis. This has
nothing to do
with the cpu or any other thing. It has nothing to do
with induction
afaik.




Just for fun I measured those values on a atx psu
connected to a 100W
load, trough a insulation xfmr. I measured 60-65V, and
70µA. This
current is so tiny you won't normally feel it, so no
danger to human
beings. However, if some equipment is earthed, and some
not, it might
destroy electronics.

According to several references, GFCI designed for personnel
protection will trip when leakage current exceeds 5
milliamps.

Dimitrios Tzortzakakis wrote:

Then why is a computer in a fully enclosure metal case?

Because its pretty hard to make a computer double insulated.

Provided, that
a computer works with voltages not higher than 12 volt,
and the PSU
is already shielded, why not put it in a plastic case?

See laptops - computers that have voltages 20 volts
entering their cases and have plastic cases.

Dimitrios Tzortzakakis wrote:
Then why is a computer in a fully enclosure metal case?Provided, that a
computer works with voltages not higher than 12 volt, and the PSU is already
shielded, why not put it in a plastic case?

Because of RF emissions.
It can/will make inteference with other electronic equipment, but it is
not the RF that induces the voltage.
Besides, notebooks is plastic cabinets... And so is the plexiglass
cabinets that is commonplace those days. But you require a common
ground, and so metal is practical, in favour of running a ground cable
to every device.
Also metal is more durable than plastics.
But yes, a computer emits _huge_ mengths of RF, enough to disturb a
radio, but not enough to induce 60V in the chassis. Maybe a few µV.


--
MVH,
Vidar

www.bitsex.net

Arny Krueger wrote:
Dimitrios Tzortzakakis wrote:


Then why is a computer in a fully enclosure metal case?


Because its pretty hard to make a computer double insulated.

No, not really. The 12V is 12V from ground. Not some 1xx volts from
ground, so it'd not have to be double insulated. The PSU would have to
be, and that would be pretty easy.

Provided, that
a computer works with voltages not higher than 12 volt,

and the PSU

is already shielded, why not put it in a plastic case?


See laptops - computers that have voltages 20 volts
entering their cases and have plastic cases.

And doubly so because the PSU leakage is capacitors connected to
gnd/midpoint _on purpose_.

Yes bad habit, replying to post and posts child.

--
MVH,
Vidar

www.bitsex.net

On Mon, 13 Jun 2005 14:57:40 +0300, "Dimitrios Tzortzakakis"
wrote:

Then why is a computer in a fully enclosure metal case?Provided, that a
computer works with voltages not higher than 12 volt, and the PSU is already
shielded, why not put it in a plastic case?
To provied FCC (and other regulatory) EMI shielding. Many of those
plastilc looking cases are either coated or contain carbon or other
conductive material. See FCC rules, Part 15

, _
, | \ MKA: Steve Urbach
, | )erek No JUNK in my email please
, ____|_/ragonsclaw
, / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org

Arny Krueger wrote:

According to several references, GFCI designed for personnel
protection will trip when leakage current exceeds 5
milliamps.


Yep, which is _far_ from 70µA. But in Norway, the norm is 30mA. However,
Norway has a IT-net, not a TN-net. (Or was it TT? Never remember the
difference :P)


--
MVH,
Vidar

www.bitsex.net

On Mon, 13 Jun 2005 14:54:01 +0300, "Dimitrios Tzortzakakis"
wrote:

If that happens, then why does not my GFCI breaker trip?

--
1) the leakage current is below the GFIC trip threshold (this is
likely, as the threshold would be set to prevent 'nuisance trips)
2) the GFIC breaker is defective or improperly installed.
3) You are not plugged into the circuit protected by the GFIC breaker
, _
, | \ MKA: Steve Urbach
, | )erek No JUNK in my email please
, ____|_/ragonsclaw
, / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org

Vidar Løkken wrote:
Arny Krueger wrote:

According to several references, GFCI designed for
personnel
protection will trip when leakage current exceeds 5
milliamps.


Yep, which is _far_ from 70µA. But in Norway, the norm is
30mA.

In the US - we consider 30 ma to be the limit for protecting
equipment. The threshold for protecting personel is 5 ma.

Arny Krueger wrote:

Yep, which is _far_ from 70µA. But in Norway, the norm is

30mA.

In the US - we consider 30 ma to be the limit for protecting
equipment. The threshold for protecting personel is 5 ma.



Yep, which relates back to that in a IT-net you have insulation between
the midpoint in xmfr and gnd, that also limits the current, while in the
US you have a TN net where gnd is connected straight to the mid-point.
Don't ask me to explain the differences, I only know that the norwegian
system is considdered safer, and there's two countries that is using it.
Norway and Peru or something like that.
So we have 2 wires, with a potential to each other of 220V, both being
"hot" relative to gnd.

Perphaps someone else in here can explain the difference between a IT
and a TN/TT net?

--
MVH,
Vidar

www.bitsex.net

Vidar Løkken wrote:
Arny Krueger wrote:

Yep, which is _far_ from 70µA. But in Norway, the norm
is

30mA.

In the US - we consider 30 ma to be the limit for
protecting
equipment. The threshold for protecting personel is 5 ma.



Yep, which relates back to that in a IT-net you have
insulation
between the midpoint in xmfr and gnd, that also limits the
current,
while in the US you have a TN net where gnd is connected
straight to
the mid-point.

See reference, below.

Don't ask me to explain the differences, I only know
that the norwegian system is considdered safer, and
there's two
countries that is using it. Norway and Peru or something
like that.
So we have 2 wires, with a potential to each other of
220V, both being
"hot" relative to gnd.

Perphaps someone else in here can explain the difference
between a IT
and a TN/TT net?

http://www.mikeholt.com/documents/mo...gworldwide.pdf

pp 7-8

Arny Krueger wrote:

http://www.mikeholt.com/documents/mo...gworldwide.pdf


Thanks a lot That was a quite informative pdf, actually I should've
remembered my electrical installations book was 2 meter from me...
Thought I'd sold that book after last year, but anyway, that PDF
described it better than the book!

pp 7-8

I had a peek at the rest...


--
MVH,
Vidar

www.bitsex.net

On Sun, 12 Jun 2005 21:33:53 -0500, Jim Adney
wrote:

Sure, it's 60V as seen on a 10 MOhm meter, but the source impedance is
on the order of a MegOhm. That's never going to provide enough current
to be dangerous. Of course that assumes that all his components remain
in good condition. If something actually fails, then you're right and
he is without a safety ground.

Right on both points. It's that pesky second point that bothers me.
In addition, that small but probably continuous current could be
damaging to sensitive components; remember we're dealing with a
computer and a cable modem here, lots of low voltage, low current,
high speed "stuff" that could be damaged by strong transients.

An interesting but flawed solution is to connect the power strip
"ground" to the shield of the modem. That would give the strip a
return reference, but one fraught with difficulty on a number of
levels - power currents injected into an RF shield being the most
conspicuous. I don't like it. I'd get an electrician.

--
Al Brennan

"If you only knew the magnificence of the 3, 6 and 9,
then you would have a key to the universe." Nicola Tesla

--
Tzortzakakis Dimitrios
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
? "Steve Urbach" ?????? ??? ??????
...
On Mon, 13 Jun 2005 14:54:01 +0300, "Dimitrios Tzortzakakis"
wrote:

If that happens, then why does not my GFCI breaker trip?

--
1) the leakage current is below the GFIC trip threshold (this is
likely, as the threshold would be set to prevent 'nuisance trips)
The threshold in europe is always 30 mA.
2) the GFIC breaker is defective or improperly installed.
It's a new Siemens GFCI breaker I installed myself, and I hope I can install
one correctly.
3) You are not plugged into the circuit protected by the GFIC breaker
, _
The breaker protects my whole house.
, | \ MKA: Steve Urbach
, | )erek No JUNK in my email please
, ____|_/ragonsclaw
, / / / Running United Devices "Cure For Cancer" Project 24/7
Have you helped? http://www.grid.org

On Tue, 14 Jun 2005 14:55:33 +0300, "Dimitrios Tzortzakakis"
wrote:

The breaker protects my whole house.
Ah!
the difference between international systems.
The US residential mainly requires only certain Branch circuits to be
GFIC (and now ARC fault) protected. Newer 'Industrial' systems have
the "whole" service panel version.

, _
, | \ MKA: Steve Urbach
, | )erek No JUNK in my email please
, ____|_/ragonsclaw
, / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org

Get an outlet tester. They plug into the outlet and let you know if it is
wired correctly.

I believe you will find that you have an outlet with the neutral and hot
reversed.

How is your internet connection? In my experience this can cause wicked
packet loss.


"Howard Knight" wrote in message
...
First, let me tell you that I'm a retard when it comes to electronic
stuff. Anyway...

I was fiddling around behind my computer and got a nice shock. I'm
trying to figure out this problem and am hoping you folks could
help me out.

I get the shock when I touch any part of the back of my computer or
wires, and also touch the metal part of the cable that comes in and
connects to my cable modem. Here's the deal:

I live in an older house that is not grounded. The ground prong on
the outlets isn't connected to ground or anything else. Also, I've
determined that the coax cable coming in to my cable modem is
grounded. Somthing seems to be making the ground prong on my outlet
hot. I've narrowed down the problem to my power strip. I've
unplugged everything from my outlet and I check the outlet for
voltage. Neutral to hot gives me 110V. Neutral to ground give me
nothing (actually, for some odd reason, there does seem to be a
slight voltage (less than 2V). Hot to ground also gives me nothing.
As one would expect.

Now, if I plug in a power strip and do the same check on one of the
outlets on the power strip, I get: neutral to hot 110V, neutral to
ground around 60V and hot to ground around 60V. Is this right?
I've checked this with two power strips and I get the same results.
What would cause this? Is the polarity on my outlet wrong? Or,
am I just a dummy and am misintepreting what is going on. This
misterious 60V is what give me the shock.

Howard