Grounding

[lcaillo]

Grounding

Proper grounding is essential to the protection and proper operation of home electronics. Electrical codes require that all signal lines entering the home, as well as masts for antenna systems (including satellite dishes) must be grounded to the ground rod for the electrical system.

The electrical system ground is often a forgotten part of the protection system. It should be checked for corrosion, loose clamps, and proper connections. Surge protectors need this ground to dump current from surges. If there is resistance in the ground path, surge suppression will be much less effective.

We often see problems with antenna, satellite, and cable installations with respect to grounding. Installers are often not trained in proper installation and often fail to ground the mast and the signal lines to the electrical service ground. Whenever a system is serviced, the technician should be checking for problems or old installations that might have been done before grounding was common practice. This rarely happens with the level of installer training and knowledge found with many companies.

There should be a heavy gauge wire connected from any mast to the electrical service ground point AND from a ground block at or near the entry point to the home through which the shield of EACH signal line is connected. If these connections are not found, it MUST be done to assure safety and system protection. Also, ANY additional ground rods that are installed for antenna or satellite systems MUST be bonded to the electrical service ground electrode.

Often, when grounding is not done properly, potentials exist between the points that should be ground on the various systems, resulting in hum, noise, distorted images, and possibly dangerous currents. Potential problems exist any time that there is resistance of more than a few ohms between the grounds on various systems. Any leakage current on a ground or exposed conductive surface on a component or wire that measures more than 500 micro-amperes is excessive and MUST be corrected.


See this link for more discussion of code requirements:
http://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/GroundingSatelliteDishandLead-InCables~20020303.htm

Reference documents for electrical codes:

NEC Section 810-20 re: Antenna discharge unit
NEC Section 810-21 re: Grounding conductors
NEC Article 250 part H re: Service grounding electrode

Other useful links:
http://www.dbsinstall.com/diy/Grounding-1.asp

[lcaillo]

I just did another service call yesterday and found a brand new Dish Network installation that was not grounded properly. This one was such a clear example of the misunderstandings that are pervasive on the matter AND of the problems that can result that I have to pass it on. This is not just my personal favorite soap box issue. Real problems are caused by improper grounding.

In this case, The entrance for the dish wiring to the home was about 20 feet from the electrical service entrance. The installer haddriven a new ground rod at the entry point but did not connect it back to the ground rod on the electrical service. He also did not connect the dish or the pole to his ground rod, only the shield on the coax.

Pause here.

ELECTRICAL CODES IN THE USA ARE VERY CLEAR. YOU MUST GROUND THE MAST OR POLE AND THE COAX SHIELD TO THE ELECTRICAL SERVICE GROUND ROD AND IF YOU DRIVE A NEW ONE YOU MUST BOND IT TO THE ELECTRICAL SERVICE GROUND.

Every owners manual for a device using an external signal source like a TV or Sat receiver has, in the first few pages, instructions for doing it correctly and a diagram specifying these connections.

So why is this such a big deal? The installer probably thought he was doing a great job, adding a ground rod when he did not need to. All of the work was very neat. The answer is that all grounds are not created equal, nor do they remain the same. I went out on this call because the TV would not come on. It would try to start and go into some strange locked up mode with no high voltage, but also no diagnostic code. On a Sony this is very unusual, as they normally have a blinking LED code if they shut down after trying to start. I immediately unplugged the set and plugged it back in and it started...ah, just a latched up micro or something tying up the data bus. A manual reset fixed it. Now why would that happen. Looking at the surge suppressor I noticed that the coaxial connections were not going through it. OK, this was originally a cable installation and the surge suppresor was not designed to pass the d.c. to the LNBs needded in a cable system. So I disconnect everything to install a sat surge suppressor, and make some measurements. The coax for the satellite does not read continuity to the a.c. outlet ground. I have only a few ohms between the nuetral and gound , so that is ok, but not only do I not have a connection, I have 14.5 volts on the coax shield. I also noted a slight shock when my arm was touching the case on the satellite receiver and my hand was holding the coax shield. Not enough leakage current to be unsafe, and it does drop of with time, but likely enough to freak out a microprocessor. It is not uncommon to have induced voltages between isolated systems or grounds that do not actually provide a current source. The problem is that when a current source becomes present such as when lightning strikes or a static charge builds up, there should be a connection that drains it to ground. Not so here so the TV micro locked up.

So why would driving an extra ground rod on an installation like this be the WRONG way to do it? It was only 20 feet from the electrical service ground rod! Well, this part of Florida is in many places just a big sand pile on top of limestone that may be at the surface or dozens of feet below. Sand is not a very good support for electrical conductivity. Even in the soaking rains that we have had recently, it drains away almost immediately. Also, the electrical service ground connection was buried and probably never checked in the nearly 30 years since the home was built. It was corroded, so even if the soil provided a ground connection, the two grounds in the home would have been at different potentials. Where there is resistance, there can be a voltage difference. Add a source for current and you have problems.

This is just one more in a long example of improper installations. The installer probably thought he was doing a good job. He would have been much more effective to have simply run the ground over to the a.c. service electrode (ground rod) and cleaned up those connections. I see these installations constantly. A week hardly goes by that I do not find at least one on my service calls, usually several. This one was an example of a problem that was likely caused by this kind of installation practice.

[jeff68925]

Be very careful about adding ground rods to an existing system. Improper placement will change the impedance of the ground. In my work, I have had to call in a physicist to work out oddball issues. There should be an electrician somewhere in your area that can measure the ground resistance. I shoot for .3 ohms or less. Sometimes that is not possible without installing chemical grounds. Also, ground rods do go bad. Sandy alkali soil will dis-integrate rods in 5 years or less.

[lcaillo]

There should be no reason to install ground rods in most systems, and if you do, it is necessary to bond them to the electrical service ground electrode anyway.