|  | 
Protect Your Property – What everyone needs to know about the importance of Ground Bars
Lightning protection is the process of directing strikes to ground and away from where they can cause damage or injury. The fact is lightning wants to be absorbed into the surface of the earth. To protect ourselves, our homes and businesses and everything inside, we need to give lightning a path to the surface of the earth that bypasses things we want to protect. Doing this correctly requires a properly designed, low-resistance grounding system. Many buildings have grounding systems that meet electrical codes, but many of these systems were installed when codes were not strict and detailed. Many of these systems have been added to and modified by different contractors over the years, without a thorough understanding of grounding as a total system. Grounding and its maintenance is commonly taken for granted. A total systems approach to lightning protection is needed for every electrical installation.
A large scale example can be found in central Florida. The Orange County Emergency Response System had been losing over $100,000 worth of equipment, per year, before they had their system inspected and upgraded. Of course, not everyone operates a 280 ft. antenna tower, located in “Lightning Alley “, but we will use this case as an extreme example. The tower had a complete grounding and lightning protection system installed 10 years ago. When checked, the resistance to earth was an astonishing 550 ohms (there was not clear path for lightning to reach the surface of the earth). This reading is 22 times the maximum resistance cited by the National Electrical Code, and more than two orders of magnitude higher than the level recommended by the IEEE and TIA/EIA. It was discovered that the tower was connected to a length of steel all-thread instead of an approved ground rod. To correct this, a new 60-ft copper clad ground rod was installed. This resulted in an acceptable 4.3 ohms resistance.
They also found equipment chassis had not been bonded to their racks. During a thunderstorm in mid-2002, a leak in the building’s roof left a trail of water down one of the racks and onto the concrete floor. A lightning strike followed the moisture trail, destroying expensive transmitters and leaving the 911 system short by two communication channels. This was corrected by connecting all equipment chassis and racks to a series of ground bars mounted at the top of the overhead rack supports. These ground bars are connected to each other in a halo ring and directly connected to the new grounding electrode system.
This is the most common use for a ground bar. The ground bar provides a termination point for many devices, and is usually connected to a ground rod by a single large conductor. A ground bar is generally used to prevent running cable from every device out to the ground rod. This saves a considerable amount of wire, and eliminates the clutter of multiple connections directly on the ground rod. An interesting note, one of the growing applications for ground bars is in home theater systems. Individual ground wires connect the valuable video and sound equipment to a ground bar. This ground bar is then connected to a copper clad rod buried in the earth.
The major considerations when choosing a ground bar are:
1) The number of connection locations currently needed.
2) The number of spaces needed for future expansion.
3) The conductor size and corresponding terminals to be used.
Ground bars are most often sold as a kit, including the copper grounding, standoff insulators and mounting brackets. These start at 2” X 10” in size and go up thru 4” X 72”. Most ground bars incorporate a standard NEMA 3 hole pattern for bolted connection to standard compression lugs made by Burndy, Ilsco, Panduit, T&B and others. If a standard ground bar will not suit your application, custom fabricated ground bars are available. Ground bars can also be electroplated to protect the copper bar from corrosion. This is especially important if the copper bar is exposed to the elements.
Keep in mind, your local building inspector can be a great source of information for the appropriate grounding precautions to take in your area. But one thing is for sure, with the growing expense and sophistication of appliances, entertainment equipment and computers, home and business owners must be proactive in providing an adequate grounding system.
|
| | | |
