Grounding of Plasma TVs and other expensive stuff

[pfalcon]

... that allows 120Hz ripple to flow through the shield. This then corrupts the video signal...

That would be the harmonic ripple caused by the ground being at the same potential as the neutral. Current flows from both the Hot and the Neutral which you can prove with a pair of diodes. True audiophiles use a ground at the midpoint of the voltage. The leads are then +60VAC and -60VAC instead of +120VAC and 0VAC. The equipotential voltage from ground self-cancels the 120hz harmonic ripple. It has nothing to do with a ground loop but it does have to do with the ground.

This is also why that minister died in the baptismal last year. They clipped the ground to eliminate the buzz on the microphone.

 

[jaylectricity]

Current flows from the TV hot lead through an EMI filter capacitor out down to the internal chassis ground then out through the cable in shield, to the cable bonding point,then to the service bond, to the neutral then back to the TV set. A complete current path that allows 120Hz ripple to flow through the shield. This then corrupts the video signal.

Is that where the "rolling bars" of discoloration come from? I've been told to defeat the ground to the TV/Monitor with an adaptor if there seems to be no other alternative.

What would the other alternatives be? What about the circuit should I be investigating to correct the situation?

 

[earshavewalls]

First, by not using the ground or plugging into an outlet without a ground, you void the warranty, violate the U.L. listing that the equipment came with, and if there is any kind of fire or other event in the area of the TV which you file an insurance report on, if the adjuster/investigator is worth their pay, you won't be covered because of the above violated listing.
Good reasons to install as listed.

 

[dbuckley]

Is that where the "rolling bars" of discoloration come from?
What would the other alternatives be?

Hum bars are common in video systems, almost always due to ground loops.

transformer isolation of the video is pretty much a sure cure. The problem is endemic in CCTV systems, as there are often coax feeds from cameras which are powered locally to the camera, and then theres hundreds of feet of coax to the multiplexor or whatever, and ground systems are never equipotential down to millivolts. So you fit a HumBug

Lots of info available at ePanorama in the section Ground loop problems in video lines

 

[iwire]

Current flows from the TV hot lead through an EMI filter capacitor out down to the internal chassis ground then out through the cable in shield, to the cable bonding point,then to the service bond, to the neutral then back to the TV set. A complete current path that allows 120Hz ripple to flow through the shield. This then corrupts the video signal..

Lets assume that is a fact.

An EGC will not prevent that.

The current would split between the EGC and the shield.

I will stick with my post and say a ground loop is not possible without the EGC.

 

[ELA]

Very true. I agree. This is why the +/-60volts balanced power system is good, as mentioned by pfalcon. In this system the two out of phase and equal (ideally that is) capacitor currents cancel and thus no problem with what I improperly refered to as a ground loop. Perhaps earth leakage current would have been better to say. My bad.

Yes when the ground prong is connected then the currents divide. I imagine in most cases the cable shileld may be a lower impedance than the house electrical ground system. This often results in hum bars in video.

Because the capacitive earth leakage currents divide between the power plug ground and the cable ground ( in varing degrees ) it can be difficult troubleshooting those types of problems.

 

[John Valdes]

Televisions don't know if they are grounded. They will still work. But you know if it is grounded or not. It should be GROUNDED. The power source and the coax.

 

[iwire]

Televisions don't know if they are grounded. They will still work. But you know if it is grounded or not. It should be GROUNDED. The power source and the coax.

Really?

I have 5 televisions in the house and not one has a grounding type cord.