All electrical systems use an earth ground. When electricity is generated at a large power station, the return path for that electrical power is made with the earth.
Failure to make contact with the earth in the ground system will cause electricity to flow elsewhere. In many cases, that pathway is through the human body and then into the earth that person is standing upon, causing electrocution.
This is why a working system earth ground is so important in an electrical distribution system, especially for older-style fuse boxes. The earth ground is electrically and mechanically connected to the earth through a long copper rod and a bare copper wire.
The Ground Rod
The ground rod is made from a 5/8-inch diameter metal rod that is either coated with copper or a galvanized coating to resist corrosion. The length of the ground rod may vary for application, but typically comes in either a 6-foot or 8-foot length.
The best length of rod to use is the longest. Certain underground formations may prohibit the use of the longer ground rod.
The ground rod is driven into the earth just below the point of entry for the electrical service. This is generally below the placement of the power utilities meter location.
Once the ground rod is driven into the earth, a ground rod connector is secured to the upper portion of the rod. Generally 4 inches to 6 inches of the rod is left exposed for this connection.
Connect the Fuse Box
A bare copper wire ranging from 8 gauge to 6 gauge in diameter is attached to the ground rod connector. Check with local code regulation for sizing of the ground wire.
The bare wire must be protected from any mechanical damage when being run outdoors or through any wall cavities. This entails placing the ground wire in either a solid metal conduit or a flexible sheath.
The bare copper wire is then connected or terminated to the metal frame of the old fuse box. A solid metal terminal bar must also be used for this connection.
All neutral wires and grounding conductors are then electrically connected into this metal termination bar. A secondary wire is also connected from this bus bar to the power company's neutral wire, completing the safety circuit.
Consult the power utility company because local electrical connections may vary in different parts of the country.