ECN Forum Forums General Topics of the Trade General Discussion Area IWire...or any other commercial guys.....(especially retail....)

This same problem has occurred in other stores across the country.

The entire store had an issue with the grounding.

You also mentioned that you have not checked the transformer(s)

I have regrounded stores where misc. hard to define computer problems were happening. The procedure was to drive a new copper ground rod, sometimes 2, loop a run of # 1/0 between them, through the gutter beneath the panels, then bonded the ground bars and cans of each panel with bronze lugs on sanded surfaces back to the big 1/0, with #2 into each panelboard. This was also attached to bldg. steel. You have probably already read the thread about grounding transformers from a few days ago, and as somebody else said, this is probably an art. 250 violation. Not saying that it is not a more sophisticated/complex issue, but look at the obvious problems that might be causing your problem to go away when you use grounding adapters; if removing the electronics from the "reference point" i.e. earthing as the Brits call it, removes the symptoms, perhaps you have a lackadasical, casual, almost grounded service. Remember, the code is only the minimum standard...think about it...

[This message has been edited by Almost Fried (edited 10-29-2006).]

[This message has been edited by Almost Fried (edited 10-29-2006).]

I'd suggest trying a couple of simple tests:

1) What is the voltage difference between neutral and ground at the receptacles with everything plugged in and everything _off_. If everything is off, then there should be no voltage drop in the neutral, and any voltage between ground and neutral means another source for the problem.

2) With one of the TV sets unplugged from the power supply, but still connected to the signal cables, check for continuity between the ground pin on the plug and the electrical system ground. If you have such continuity, then this indicates that there is a parallel ground path via the signal cables. Loop area between the electrical system ground and the signal cable ground can pick up interference.

When you say 'RCA jack' that give me shivers for such a large distribution system. An RCA jack is a two terminal coaxial connector. Unless there is a separate ground strap, this means that the coax cable shield is being used as one of the signal conductors. From distant memory (confirm with other sources This is fine for a few feet in a home, but not suitable for a large system. Ideally the signal would be carried by two conductors that are isolated from ground, and then an over-all shield is grounded at _one side_ only, and is not expected to carry any signal current.

-Jon

I deal with this all the time in CCTV systems, problem is caused by current on the shield or ground of the signal cable. Most all equipment have the safety ground and signal ground tyed togeather. When you use an grounding adapter you lift the ground loop and isolate the equipment ground, no current can flow. Solutions, Make sure all equipment is served by the same panel, Use isolation transformers in the coax or signal lines. Make sure the signal line, or coax grounds DO NOT contact the bldg anyware in their run. An isolated ground ckt to all equipnent served to 1 ground point. Make sure the computer or whatever supplies the video to the displays is isolated and ONLY gets its ground from the isolated power cord. This applies to any signal distrubution equipment. Isolation transformers in the signal lines or fiber suppling the signal may be the easy way to correct the problem. Robert

"Let me just say to that the faulty distribution amp diagnosis makes sense to me, the two/three prong adapter however, it's a curve ball for me."

The curve ball is, when uses the adaper he removes the ground, and the cable stops suppling the AC fault from the distribution amp.

Ok that makes sense to me now LK. It's good to actually be able to say that too! (btw)

I'd work from the display back towards the source.
first check the display with a local test source, if clean, add the cable, and move the test source to the other end. If that is clean, add the DA without anything else connected except the test source and display under test. If that is clean, start adding other displays.
Finally, add the real source.

At the point where the problem appears, you can try adding a humbucker to the video line, and see if that cleans up the problem.

Another possible soultion might be using cat5 with baluns to isolate the video lines, instead of coax.

Mahlere, any update on the problem. Really curious if you know how it was resolved. Just twisting your arm a little!

[This message has been edited by yanici (edited 11-21-2006).]

Don't know. We determined that it wasn't in our wiring and was in the building or the A/V cables. Then we pushed it back to the engineers.

we determined that wasn't in our wiring...it was in the building or AV cables

I am curious if you ever opened up the transformer and source panel{s} to check if the N-G bond was there?

No to the transformer. We did open the source panels, everything was fine. What we did was run a temp line straight from the panel we fed out of, to the units (a couple of MC cables straight from the source so to speak) had the exact same issues.

So the problem was either in their A/V cables (since the entire store came out of these panels with no problems) or there was an issue with the neutral/ground feeding these panels.

Either way, it was out of our scope of work and was passed along to be addressed by those with more stripes on their shoulder than me.

For the record, I'm not taking the front cover off a tranformer while it's live...