GROUNDING & LIGHTNING PROTECTION
The importance of the grounding system (or earthling systems elsewhere in the world) in your building cannot be overstated. The grounding system is the foundation upon which great power quality is built. The grounding system is also the backbone for the electrical safety of your facility. A bad or shoddy ground can cause so many problems that you can keep a squad of electricians busy through out the year. Talking to many electricians and power quality experts, as well as reading articles written on the topic of power quality, we see that anywhere from 60% to over 75% of all building power problems are related to grounding.
The three basic thoughts for grounding worldwide are to have no grounding systems, low resistance grounding, and high resistance grounding. Each style has followers and detractors. The bulk of you will be dealing with a low impedance ground which is pretty much the standard in the US, so that is what we will focus on. If you have questions on high resistance grounds give one of our experts a call and we will help answer your questions.
The first step in a great grounding system is the ground. By this I mean that the system will only be as good as the soil or earth that your system is embedded in. If you have critical equipment, like high end manufacturing, a critical data center, etc. you should ALWAYS do a soil resistivity test. Areas with highly resistive soil can be changed by using bentonite clay, or other specialty soil fill materials that are available from companies like Lyncole XIT and Erico.
The next step is the consideration of the ground rods themselves. The choices are galvanized steel, copper bonded, stainless steel, and chemical ground rods. The galvanized and copper bonded tend to be 5/8" diameter. The UL and NEC require an 8foot ground rod.
The galvanized rods tend to be less expensive, and have a lower tensile strength (50,000- 60,000 psi). The galvanized rods are coated with zinc (approx .0039" to meet UL) The galvanized ground rod will tend to be affected by the soil conditions over time. It has been found that Galvanized rods underground tend to lose its resistance to corroding. The National Bureau of Standards has shown that a galvanized ground rod should see approx a 10 year life in average soil. As the ground rod corrodes, it becomes less effective.
The next level is a copper bonded ground rod. The copper bonded rod will be very similar in function in the first part of its life, but it will not corrode as quickly. The reason for this corrosion resistance is that it is coated with copper to .010" to meet UL (UL467). This thicker coating helps the copper rods have an average of 40 year life according to the National Bureau of Standards in average soil. The copper bonded rod tends to be a better choice because of the longer functional life.
The next rod is the stainless steel ground rod. These are also listed under UL467. These tend to be very expensive, and I do not commonly see them being used.
For areas where the soil is a real problem like we see in the Coachella valley, or some applications that I have seen in Arizona, people will be more likely to use a chemical ground rod. These are copper tubes (traditionally 2") that are filled with electrolytic salts that will leach into soil as the salts dissolve.
If the soil resistivity is too high a cheaper alternative could be to increase the contact area for the ground rod to the soil. Options include using parallel ground rods spaced a minimum of the depth of the ground rod (NEC mandates a minimum of 6' between parallel rods), but ideal would be at least two times the depth of the ground rod.
The next option is to increase the diameter of the ground rod, which will give a slight increase in the amount of contact area. According to Chris Rempe at Erico, doubling the diameter of a ground rod only reduces resistance by 10%.
The final option is usually to increase the depth of the ground rod. this is usually achieved by joining two ground rods together. Doubling the length of the ground rod decreases resistance by 40% according to Erico. The three most common choices for joining two rods together is exothermic welding, compression couplers, and threaded couplers.
Now that we have sorted your grounding issues at your facility, it's time to look at lighting protection. Luckily we live in Southern California, so we do not have the problem like some areas do.
LPI publication 175
UL publication 96A
NEC 250.60 (air terminals and driven ground rods)
NEC 250.106 Lightning protection systems must be bonded to the building or structure power grounding electrode system.
NFPA 780 "The Standards for Installation of Lightning Protection Systems"
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This site was last updated 02/06/08
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