Grounding Rods
Ground rods are often selected on the basis of their resistance to corrosion. The other major factor is the cost. All too often, the cost of a product is seen as the initial, up front price, but the real cost is determined by the serviceable life of the ground rod.
Galvanized steel rods are one of the cheapest electrodes available. However, they are not the most cost effective since they have a relatively short service life. Solid copper and stainless steel rods have a long service life. However, they are considerably more expensive than galvanized steel rods. In addition to this, solid copper rods are not suited to deep driving or even driving short lengths into hard ground, without bending.
As a compromise, steel cord ground rods, swaged in a copper or stainless steel sheath were developed. These ground rods are much less expensive than their solid counterparts. They are capable of being deep driven. However, the sheath of this rod type has been known to slip or tear, particularly the copper version. Once this sheath has been damaged, the integrity of the entire electrode is at risk. (Figure 1) shows copper bonded ground rod versus galvanized ground rod.
Figure 1. Copper bonded ground rod versus galvanized ground rod
The copper bonded ground rod has an electrolytic coating of copper deposited over a layer of nickel. This process ensures a long lasting, molecular bond between the copper layer and the steel core. Recommends copper bonded ground rods because the copper coating will not slip or tear when driven nor will it crack if the rod is bent. The tough, carbon steel core has good characteristics for deep driving. Copper bonded ground rods have a high resistance to corrosion and provide a low resistance path to ground.
The Stainless Steel Option
It is important to note that certain soils and land fill areas may not be compatible with copper. In these situations, stainless steel is a better proposition. Stainless steel may also be an alternative, where structures or components, such as steel towers, poles or lead sheathed cables are in close proximity to an array of ground electrodes. In these circumstances, consideration must be given to the consequence of galvanic corrosion. The high cost of stainless steel rods prohibits their widespread use. (Figure 2) gives Photo shows two ground rods subjected to the same pressure load test.
Figure 2. Photo of two ground rods subjected to the same pressure load test
The copper bonded ground rod, shown on the left, will bend without tears, cracks or folds, to the outer sheath. The inferior copper clad rod shown on right, has developed cracks and creases to the outer sheath, which will significantly reduce its serviceable life and put the integrity of the entire electrode at risk. (Figure 3) shows the ground rod life expectancy and (Figure 4) shows the ground rod annual cost for different rods types.
Figure 3. Ground rod life expectancy