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Document ID: PEN1008
Copper ground rods are really copper clad steel! What affects them, their installation and use.
The real reason for copper plating is corrosion resistance. Copper, silver, mercury and gold have high resistance to corrosion, while processed metals like aluminum and
magnesium are easily corroded. Noble metals like copper become the cathode when joined together with less noble metals in the presence of an electrolyte (water). Less noble metals become the sacrificial anode
and corrode away.
Not listed in the galvanic table of metals is Graphite, since it is not a metal. Graphite is even more noble
than silver and certainly much nobler than copper. Therefore, if a graphite backfill material is to be used as
a ground “enhancer” to surround copper, the copper will be sacrificial to the graphite and will dissolve away
into the soil.
The following affect the amount and speed of corrosion both above
and below the soil:
- Water. The presence of water mixed with contaminants is the basis
of galvanic corrosion. Pure rain water is slightly acidic (pH 5.5 to 6.0). It picks up carbon
dioxide as it falls which creates carbonic acid. It can start attacking some metals, even copper,
without being in a junction. The ions etched from the copper go into solution in the
rain water. As this rain water drips on galvanized tower sections, it will cause the zinc to combine
and wash off. This leaves the bare steel to oxidize away.
- Oxygen. This is the main corrosion accelerator. Rain water also
picks up oxygen as it falls through the atmosphere. Water provides an excellent carrier of oxygen.
- Temperature. Generally, the higher the temperature the faster
the chemical reaction.
- Texture of the metal(s). Glass smooth surfaces are less likely
to corrode than rough finishes.
- Hydrogen Sulfide. A gaseous product of exhaust emissions, it combines
with rain water creating acid rain.
Chlorine. Tap water can have an acidic effect on underground materials.
- Inert gases. Helium displaces oxygen and reduces the corrosive
- Alkaline. Although some alkalis tend to increase the rate of carbon
dioxide absorption from the air, which creates corrosive carbonate solutions, slight amounts
of alkalinity can reduce corrosion rates.
- Salts. Sodium chloride, found just about everywhere, increases the soil conductivity and also
Why Steel Ground Rods are Copper Plated Document ID: PEN1008
- Salts. Sodium chloride, found just about everywhere, increases
the soil conductivity and also increases the corrosion process in nearly the same proportion to
its concentration. Other naturally occurring salts or non natural added salts do the same. Only sodium
carbonate or phosphate and potassium ferricyanide form a protective film that prevents further
- Microorganisms. Both bacteria and fungus can deteriorate metal. Some will give off acids in
trapped water or when they die and decompose into acids.
Types of Corrosion
There are several types of corrosion. Listed below are the common
names given for descriptive purposes:
- Uniform Etch: A direct chemical attack from salts, urine and acids.
If allowed to continue, a polished surface will dull and then take on a rough or frosted appearance.
- Pitting: Tiny pin holes from localized chemical or galvanic attack.
- Inter-granular: Usually galvanic, this is a selective attack along
the grain boundaries of an alloy metal. We have referenced this as “de-alloying.” Typical
corrosion-resistant alloys can break down when corrosion actually works on the individual components of
- Exfoliation: Found on extruded metals, the corrosion occurs just
below the metal surface and causes a blister to form. This appears where the extruding dyes have
forced the crystal structure of the metal to change direction.
- Galvanic: The classic two dissimilar metal connection with a water electrolyte bridge is the most
basic of corrosion problems.
- Concentration Cell: As the amount of oxygen reaching the electrolyte
varies, the rate of corrosion will vary accordingly. High concentrated areas of oxygen will have
high levels of corrosion.
- Stress: More corrosion will occur where high tensile stress is
applied. This is where metal is bent or where rivets have been driven. Metals that have been cold worked
(bent back and forth several times) should be annealed (stress relieved by heating). Stress
corrosion appears as a crack running parallel to the metal grain.
- Fatigue: Another form of stress corrosion where pits are defined
along the grain. Additional stress begins to concentrate around them and cracking occurs at the
bottom of the pits.
- Filiform: Thread-like filament corrosion occurring under painted
surfaces where water and oxygen have penetrated and form a corrosion concentration cell.
Why Steel Ground Rods are Copper Plated.
- Mother Nature will see that nothing we place in the soil will last
forever. But we can do our part to design a grounding system that lasts.
- Use all similar metals in your grounding system. If copper is used, don’t mix in tin plated copper wire.
- On mechanical compression joints, copper joint compound should be used to cover the hardware. This will prevent corrosion that can cause a loss of compression strength
and increase joint resistance over time. The joint compound, a petroleum based product with conductive copper flakes, displaces water, oxygen, acids and salts.
- Exothermic connections should be allowed to cool slowly to prevent stress corrosion.
- A grounding system should be tested annually.
- Grounding systems should also be checked annually for corrosion.
- Know your soil’s pH (See notes on soil pH testing). If acidic, either correct it to neutral or suffer the consequences.