Kooshballa,
Just to be safe you should check out how the CATV provider coax cable grounding block is earth connected.
NEC Code requires the Grounding Block to be connected to the main grounding system of the house.
On the outside of your house locate where the CATV cable connects to the house. Follow the cable and look for where it enters the house. Close to the cable entry of the house there will be a small grounding block that the cable connects to. In some cases the block will be protected inside an accessible enclosure.
The grounding block is for lightning protection which provides a low impedance, resistive, path to earth.
The block should also be at the same ground potential as the grounding system of your home. In your case it may not.
The ground loop hum is caused from a difference of potential, voltage, between the shield of the coax cable and the safety equipment grounding conductor of the branch circuit/s, that feeds the associated connected audio equipment that uses the safety equipment ground.
The difference of potential could be caused from a loose or corroded connection in the CATV coax grounding block connection to the grounding system of the house. Or the difference of potential could be caused from a loose or corroded connection of the safety equipment ground.
What ever the problem, the ground isolator will stop the ground loop hum.
What the isolator does not do is correct a possible serious CATV cable grounding problem.
You should make sure the CATV provider coax cable block is properly connected to the main grounding system of your home for lightning protection.....
Things to look for,
Is the ground wire that connects to the grounding block to the house grounding system, loose, corroded, or the connection is broken.
Remedy... Clean connections and re tighten.
In older CATV cable installations it was common to see a separate ground rod driven in the earth and the grounding block was connected to the ground rod. Or worse yet a short ground stake was pushed into the earth and the grd block was connected to the stake. The ground rod was not connected to the main grounding system of the house.
This is a no no. For lightning protection this type of installation must be corrected.
You should take the time and look for the grounding block, then follow the path the connected ground wire takes, and where the wire connects to the main grounding system of the house.
If you take the time to check, post back your findings.
I will let you know if the grounding method is NEC code compliant.
There are a few ways NEC allows where the connection to the main grounding system of the house can be connected. One example, NEC allows the connection be made to the outside metallic conduit of the electrical service. IMO, not the best place to make the connection.
Jim
