Earthing in TV

S

siliconmike

Guest
I just bought a new TV and found

1. it had no earthing pin in its power cable (only Phase and Neutral
were there)

2. its audio GND (accessible from RCA connector) showed me presence of
voltage when I touched a screw-driver-cum-mains-tester to it.

3. I tried to touch the audio GND, but did not get a shock.


First, why was the TV GND floating (meaning, not earthed) ?

Can I safely connect my PC audio output to TV audio input ?

What if I manually earthed the TV GND ?

Thanks
Mike
 
Art wrote:
Designed with isolation between the chassis reference and any
externally
accessable connectors. Voltage you are measuring ar the avio
reference is
probably a result of static charge induced when the set in energized.
Click to expand...
One thing that comes to mind is that the TV power connector might not
have an earthing pin to protect it from lightning striking the antenna.
Since the whole TV electronics is floating, lightning voltages (which
are relative to earth) might prove to be less damaging.

Any responses to my other questions below..?



"siliconmike" <siliconmike@yahoo.com> wrote in message
news:1116664802.092333.281110@g14g2000cwa.googlegroups.com...
I just bought a new TV and found

1. it had no earthing pin in its power cable (only Phase and
Neutral
were there)

2. its audio GND (accessible from RCA connector) showed me presence
of
voltage when I touched a screw-driver-cum-mains-tester to it.

3. I tried to touch the audio GND, but did not get a shock.


First, why was the TV GND floating (meaning, not earthed) ?

Can I safely connect my PC audio output to TV audio input ?

What if I manually earthed the TV GND ?

Thanks
Mike
Click to expand...
 
First, why was the TV GND floating (meaning, not earthed) ?

Because it's chassis ground, or signal common, neither of which is
Earth
ground. (obviously, because the set is fully isolated and has no
Earth
pin).
Click to expand...
Sure, I know that, but what reasons did they have in not introducing
the Earth pin to short the signal common to the Earth..?
 
w_tom wrote:
First some definitions and concepts. Then some simple
experiments.

Your are confusing earth ground with something called safety
ground. Your TV has no safety ground connection because a
third ground inside the TV is isolated - a floating ground. A
voltage difference between a floating ground and safety ground
is undefined. It may or may not harm you if you touch both
simultaneously.

In the meantime, anything conductive outside of that TV must
be galvanically isolated from floating ground. Isolated does
not mean no electrical conductivity. Isolated means minimal
electrical connection.

Two tests for sufficient human safety. First, plug the TV
into a working (and pre-tested) GFCI outlet. Connect a jumper
cable from that audio ground to the safety ground (ie a screw
holding the wall receptacle cover plate). This test should
not trip the GFCI. Some current will pass from that audio
ground into wall receptacle. Current must be so low as to not
trip GFCI.

Second, measure that leakage current using the meter set for
AC current. Measure well less than 150 microamps (0.15
milliamps) from audio ground to wall receptacle 'safety
ground'. Some leakage current should be measured. Current so
low as to not threaten human life and not trip the GFCI.
Galvanic isolation does not mean zero current. It means
minimal leakage current.

BTW, the safety ground on wall receptacle does nothing for
lightning protection. Wall receptacle does not provide an
earthing ground for so many reasons. The safety ground wire is
too long (well over 10 feet), has too many splices, has too
many sharp bends, is bundled with other non-earthing wires,
etc. Earthing is not found at a wall receptacle for so many
above reasons and due to excessive wire impedance. Earthing
for lightning protection means a short wire directly to single
point earth ground; which is different from safety ground
Click to expand...
Right, thats understood. Now since the TV has 2000W exceptionally good
audio amplifier, I would like to connect audio out from my PC to audio
in of TV.

As I understand, your mentioned example current (0.15 mA) would flow
from the TV signal ground to the Sound Card GND tracks, then to the
mother board GND tracks, then to the POWER SUPPLY gnd wire, then to the
WALL OUTLET safety GND..
(PC has earth pin)

Although this current is too small, I presume it is not worth taking a
risk. Moreover, if some static phenomenon occurs in the TV, it might
damage the PC!
 
John Miller wrote:
siliconmike wrote:
Right, thats understood. Now since the TV has 2000W exceptionally
good
audio amplifier, I would like to connect audio out from my PC to
audio
in of TV.

Has the brand of the TV been mentioned?
Click to expand...
Samsung. (I'm in India)
 
Which model Samsung TV has 2000W output??
Click to expand...
CS-29T10PA

Man this TV rocks! Now I don't need to go to theatre. I put it 10 ft
from me and watch DVDs.. Its 29".. And cost is (in US $) $600..
 
"Peak Music Power" is a term you need to become familiar with.
Click to expand...
Sure I know that, but with this TV I bet one could throw a dance party.
The sound is beautiful, and of course loud enough.

And while a
29" TV is swell, it's hardly out-of-this-world. Anyway, glad you like
it.
Click to expand...

Its perfect for the price I guess.

And in answer to the original question, yes you can connect your PC
audio
output to the TV safely (assuming the PC is safe to start with). If
it
really concerns you that there may be a problem you could hunt out
some
audio isolation transformers to put between the PC and the TV, but
unless
you paid a reasonable amount of money it would degrade your audio
response.
Ken
Click to expand...
 
Peter Bennett wrote:

Even if they're using Peak Music Power, India must use much smaller
watts than the rest of the world.

Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
Click to expand...

Peter, why not do a self analysis before posting sarcastic comments for
a nation of 1 billion ? I wouldn't be surprised if someone from India
made you feel not very comfortable for what you just wrote.
 
Gotta spread them around further.

Oddly enough when I used Samsung's site search engine I didn't find
that
model, but when I used Google it popped up. Hmmm, maybe they are a
bit
ashamed.....
Click to expand...

Well I'm not sure who should be ashamed of surfing abilities, but here
are the specs on Samsung's website found in less than a minute.

http://www.samsung.com/in/products/tv/flattv/regularflattv/cs_29t10pa.asp
 
w_tom wrote:
If wire is grounded via computer and soundcard (a common
mode connection), then no static problem exists. None.

Static is not created by the TV. Voltage leakage from a
floating ground, as described earlier, may be created by the
TV. That leakage must be so low as to not harm humans, which
means that leakage is too low to harm electronics. If
worried, then make the connections before powering computer
and TV. A redundant layer of protection.
Click to expand...
Here's what I did: Connected TV Signal earth to safety earth directly
by a thick cable (16 SWG x 10) and then connected the PC to the TV. The
tester stopped showing any presence of voltage on the TV signal earth,
and the reception is ok. PC is ok.
 
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