Vital Points

Wiring and grounding cause most reported customer problems. It is essential that the grounding system be correct and complete. A grounding system consists of two major elements, a ground rod, and a length of copper wire. The National Electrical Code (NEC) states that if one ground rod is used, it must have a maximum resistance of 25 ohms. If this cannot be achieved with one ground rod, a second ground rod must be added. It is not then required that these two ground rods be 25 ohms, but it is good practice to make them as low as possible. There will be some areas, such as sandy coastal regions, where 25 ohms cannot be reached.

Place the ground rod where it is exposed to natural ground moisture, and not covered by a concrete patio or walkway, for example. The copper wire must be size number 6 or larger, and long enough to connect all necessary ground leads to this single system.

For most structures grounding starts at the service panel. Sometimes called the main switchboard, it provides over current protection (circuit breakers) and a way to disconnect the main power for the building. A ground wire is connected from the ground bus in the power panel to the copper wire and ground rod outside the building. Ground wire size depends on the size of the service panel. This information is covered in section 250-79 and 250-94 of the NEC. At this point the service panel is referenced to earth.

Additional service panels, such as panels in a free standing garage or work shop, that are fed from the main power panel, must be grounded back to the original structure's grounding system using number 6 or larger copper wire.

  • Lightning rods are connected to the grounding system using number 6 or larger copper wire.
  • All telephones and telecommunications equipment must be grounded to the grounding system using number 14 or larger copper wire. This requirement also applies to cable television installation.
  • Common television antennas should be grounded to the grounding system using number 10 or larger copper wire.
  • If a satellite dish pole is installed, it must be grounded back to the grounding system using number 6 or larger copper wire.
  • Deep well pump motors must also be grounded back to the grounding system using number 6 or larger copper wire.
  • Water service, gas lines, and metal pipes must tie to the grounding system.
  • All grounding blocks within the building must tie to the grounding system using number 10 or larger copper wire.

Some common mistakes that are made with computer grounds revolve around the concept of an isolated ground. The isolated ground outlet is an outlet that is grounded to the facility ground via a dedicated and insulated wire. This does not mean that the outlet has a dedicated ground rod or system. In fact, by using a dedicated ground rod or system you are violating code