Grounding Electrodes
For years, manufacturers of ground rods have strived to develop technical specifications for the electrical industry which address the specific needs and applications of clients and endusers alike. One reason for stressing the importance of this was to assure that the customer would receive what they asked
and paid for regardless of who the manufacturer may be. More importantly, from a position as manufacturer, it was to assure that all sources would be submitting quotations on exactly the same basis contributing to a fair and equitable evaluation and award.
You may recall several years ago problems in the outside plant arena for the power utility, telecommunications and cable TV markets as it pertained to hardware bolts and nuts. Undersize bolts with oversize nuts (whether domestic or imported) create a unique situation which, while significant in terms of liability for the purposes of this discussion, simply did not provide the customer with what they had specified nor intended to purchase resulting in a compromised plant. Whether it is pole line hardware bolts, or a similar situation with airlines being provided with bogus quality high-strength bolts, the issue remains – give me what I specified and paid for so I may have confidence in my aerial plant construction!
First, a specification must be written. And who better to contribute to this than manufacturers who have years of experience and exposure in the industry and desire to police the problem. Surely it is a reflection of their present, and future reputation with the client.
In the ground rod and accessory market there are several specifications (and policing agencies) which govern the direction and quality of our product line. Canadian Standards Association, ETL and Underwriters Laboratories, etc. are but a few of the agencies involved with this effort. It is our goal to contribute to writing these specifications and assure that the industry complies with them long after they are accepted, specified and supported by the various technical organizations. Providing a grounding system focuses primarily on theissue of safety. Of course with the introduction of micro-circuits whose failures incur costly repair expenses, the need for good grounding practices comes to the forefront in terms of system reliability. And longevity is an important issue as the selection process of ground rod types is made largely influenced by soil make-up, temperature and moisture.
There are several products which may be used:
- Least costly hot-dipped galvanized ground rods
- Expensive copper-clad grounds rods
- More expensive stainless-steel ground rods
- Very costly chemical-ground rod systems
Each have very specific and unique advantages depending upon where the product is to be used, its expected useful life, contribution to system reliability, the cost expense outlay committed to installing the system and of course its affect on longterm safety.
Not all ground rods types meet all of the above criteria in all situations. As an example, if you install a copper-clad ground rod at a wood pole location that is guyed using a galvanized anchor rod, you may have just created a “battery effect” which will cause the zinc coated anchor rod to sacrifice to the copper ground rod. Recognizing the need to use not only the right product but in the right application as a system approach should always be part of the engineering design process.
We could simply use a bare steel rod or pipe to establish an adequate ground plane. Certain codes mandate hot-dip galvanized or copper-clad ground rods. If, on hand, the determination is made that copper is the answer because of the nobility of the metal cladding (electromotive series of metals) or because of past “trends”, then why are stainless-steel or chemical rods not used exclusively for they may fare better if this is the only consideration?
So one may conclude that simply specifying a morebexpensive ground rod system not only costs more money, but may not be the best engineered nor least costly approach. Let’s begin by considering a hot-dip galvanized ground rod system for the purpose of this discussion.
The industries perceived “migration” from hot-dip galvanized to copper-clad ground rods may have been an over-reaction due to the initial misapplication of ground rod selection from a design perspective, or a legitimate situation where soil conditions etc. may be better served with a copper ground rod system. But to unilaterally imply that all situations require hot-dip galvanized, copper-clad, stainless steel or chemical rods may very well be unsound engineering judgment.
Compliance to nationally accepted specifications is crucial. Copper-clad rods must meet NEC specifications monitored by Underwriter’s Laboratories. And galvanized ground rods must meet the requirements of ASTM A-123 (hot-dip) or ASTM B-633 (electro-plated). Two types of galvanized ground rods?
Yet another variable.
The hot-dip galvanizing process has been around for over 100 years primarily associated with hardware components including ground rods. And its performance history has been proven to be extremely reliable based upon actual in-service exposure and experience. However, zinc electroplating of ground rods is a more recent process and resulted in the writing of a new NEMA specification which has not been officially accepted, nor published, as of this writing.
One can argue that 3.4 mils of zinc properly applied (per ASTM whether hot-dip or electroplated) should produce similar service life. However, what is often overlooked is the technology of the electro-plating process and number of variables involved where if only one is compromised, the integrity of the system (or plating) may be at risk.
Chemical rod systems are designed specifically with adverse soil resistance characteristics in mind and take into account several issues not related to the galvanized, copper-clador stainless steel ground rod. Likewise, the stainless steel rod is a solid bar of 304 alloy produced to the dimensional specifications of the rod size desired. We will now focus on the two most commonly selected options; copper and galvanized.
Copper-clad rods are manufactured in accordance with the American National Standards Institute (ANSI) and Underwriters Laboratories (UL) 467 specification. In effect, the criteria includes toughness (rigidity), straightness (drivability) and plating adhesion and thickness (to assure long life). While there are varying technologies to apply the copper-cladding (generally 10 mils minimum) they frequently include an acid process (some environmentally friendly and others requiring expensive chemical waste treatment processing).
Galvanized ground rods come in two forms: electro-plated and hot-dip. Electro-plated coating generally rely on surface adhesion historically used on small hardware and fastener items. Hotdip coatings result in a metallurgical bond when the molten zinc is interlocked into the steel forming a zinc-iron layer (technically speaking the progression of layers include 1) ETA which is 100% zinc, 2) ZETA which is 94% zinc and 6% iron, 3) DELTA which is 90% zinc and 10% iron, 4) GAMMA which is 75% zinc and 25% iron followed by 5) the base metal or steel core). Hot-dip plating is a proven process used on numerous products, and has been used with proven historical performance for over 100 years. Without this complete bond with the steel core, corrosion with the electro-plated process may spread quite rapidly between the zinc coating film and steel core where it cannot be ascertained until it is too late.
Of course impact and abrasion resistance is of major importance during the installation process. This, too, is where hot-dip galvanized ground rods excel over electro-plated ground rods (e.g. drivability into rocky soil). While the outer ETA layer has a 70 DPN hardness, the ZETA and DELTA layers maintain a hardness of 179 and 244 DPN respectively which is harder than the steel core (with a 159 DPN).
So what does this mean for the specifier and user of ground rods? Be sure to investigate the soil conditions where you will be making your installation, determine the system life for which you are making your design and select the ground rod that will meet or exceed your expectations without incurring excessive costs. There is no need to have your aerial plant outlast the buried grounding system, or vice-versa.
Also, be sure to investigate the placement of dissimilar metals installed adjacent to your path which can influence your design, regardless of the ground rod types selected. And while few specifications identify ground rod resistance criteria to be met, and verified periodically, be sure you define resistance to
ground maximums to provide safety, equipment protection and system reliability.
Of significant importance to your installation is the satisfaction that you have complete confidence that your purchasing department ordered what was specified, and that what you in-fact received is what was specified. Like any other situation, any break in the process is certain to compromise the integrity of your grounding system which may result in serious personnel and equipment consequences.
Be sure to recognize that chemical ground rods are very expensive but do fulfill limited applications very well. Stainless steel rods also fulfill a need in unique situations at 8-10 times the cost of a galvanized rod. Copper-clad rods serve a specific purpose at a cost of 1.5-2.5 times the cost of a similar size galvanized rod. And there are many instances where galvanized rods can and should be used with equal performance characteristics at a significant cost savings than any of the above systems. So ground rod cost and life should be an influence in the determination of the system design since they represent a significant cost of the per mile installed plant.
In Conclusion
Be sure you have confidence in the grounding system design, purchasing is ordering what you have specified, and you have received what you originally specified and ordered. This will also provide confidence and assurance that each manufacturer’s products will be quoted on the same sound and consistent basis. There is no substitute for a complete and comprehensive designed ground rod system, installed to your specification at the least costly expense without compromising system quality or reliability.
From: Overhead and Underground T&D Handbook Handbook, Volume 1, The Electricity Forum
