Sending The Ground Rod to Earth.

Bonding is the “permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed.”

All Metallic structures in a facility that can be energized due to an earth or ground fault, static electricity buildup or lightning strikes are bonded together then connected to the electrical system earth point. This practice is called Equi-Potential Bonding. 

In some installations, the bonding loop for lightning protection is separate from the bonding loop for electric motors, cable trays, metallic pipes, and steel structures.

The electrical system earth point is the point where the grounding wires are physically connected to the earth with the aid of a grounding electrode. 

The grounding electrode generally stabilizes voltages from the power source as in the case where the neutral of a transformer is bolted to ground and driven into the earth.  the grounding electrode is also used to dissipate a static discharge to earth and provide a return  path  for AC current to go back to its source

Sending the ground rod into the earth is not just as simple as pounding a rod into the soil. there are guidelines for proper grounding. because a poorly grounded system is just as dangerous as no grounding at all.

Common grounding guidelines and their reason

Length of Ground rod

NEC and UL require that Ground rods shall not be less than 5/8 inch in diameter by 8 feet in length. It all depends on the resistance of your soil the 8ft rod ensures that most parts of the rod are in contact with the surrounding earth and there is good continuity between the rod and the earth. The resistivity of the topsoil is always higher than the resistivity of the deeper layers of the soil so a long rod goes deeper into the earth's crust where soil resistance is lower and more stable thereby offering better grounding. You could measure the resistance if the earth using ground resistance tester.

Soil Resistance

NEC 250.56 requires that the system impedance to ground is less than 25 ohms. However, the NFPA and IEEE recommend a ground resistance value of 5 ohms or less. Ideally, the ground should have no resistance at all, that is the ground should be of zero ohms resistance but in practice, there is always some resistance.

To achieve an acceptable ground resistance value, the soil could be treated with a salt such as copper sulfate, magnesium sulfate, or sodium chloride and water. Over time the salts leach into the soil to reduce earth resistivity. Cow dung is used in some cases to treat the soil because they retain higher moisture levels and have a higher electrolyte level. However, in some countries, local environmental regulatory bodies object to adding salt or heaps of cow dung to the soil.

Ground rod spacing.

If ground resistance measurements are taken and the earth resistance is well above the minimum acceptable value a second rod could be driven into the ground and NEC requires that you space the rods at least 6 ft apart. To simplify this, the distance between the rods should be equal to or a bit more than the length of the rod. Ground rods spaced less than two rod-lengths apart will interfere with each other. In other words, their spheres of influence will intersect and the resistance will not be lowered.