The Function and Importance of Earth Grounding Systems – Part One

Electricity is confusing enough when we deal with wires that are supposed to carry the current. It’s even more confusing when we talk about wires that normally don’t do anything at all. Most people have some difficulty with the concept of grounding and its cousin, bonding. We’ll try to keep it simple and take the mystery out of it.

As home inspectors, it’s important that we clearly understand these systems to provide better inspections for our clients. Whether you’re interested in becoming a home inspector or are simply looking to update your knowledge, investing some time into home inspector training is a great way to ensure that your services are the best they can be.

The good news is that it is not a very complicated or time-consuming part of your inspection. The better news is that repair or replacement is usually not expensive.

Two Types of Grounding Systems

There are two types of grounding in homes, with different functions. The equipment grounding system is the network of bare, uninsulated wires that runs through the home as part of residential branch circuit wiring installed since the 1960s. Equipment grounding systems connect to the transformer on the street and protect homeowners against electrical shock from stray electricity in the home. The earth grounding system connects the house electrical system to the earth. For this discussion, we will focus on the latter.

How It Connects the Service Box to the Earth

The earth grounding system uses a wire to connect the service box to the earth with water pipes, grounding rods, etc. This is a path for lightning or static electricity. It is not intended to carry the emergency current from the equipment grounding system to the ground. The only time this earth grounding system would carry electricity from the home would be if there were a fault in the home causing the current to flow through the ground wires in the distribution system and the neutral service wire out to the street was broken.

Lightning

Earth grounding systems help carry unexpected electrical charges from other sources away safely. For example, lightning strikes can energize components in houses. The earth grounding system can sometimes safely dissipate electricity from lightning. However, large lightning strikes will not be dissipated by a house grounding system.

Static Charges

Earth grounding systems also help to dump static electrical charges. The buildup of static electricity within electronic equipment, such as home computers, can create operational problems. This is a much less important function of the grounding wire, protecting equipment rather than people.

Electrical path for ground and neutral wires

Ground Wires/Earth Grounding Conductors

Ground wires are typically copper, and may be bare or insulated. They are typically 8 gauge for 100 amp services, and 6 gauge for 200 amp services. It is best practice to avoid splices in a ground wire, since every splice is a potential poor connection.

Where Does the Grounding System End?

 

The goal is to get the electricity to flow to the ground. This is done by connecting the earth ground wire to a grounding electrode. There are several ways to do this, including:

  • Through metal water supply pipes
  • Through metal rods driven into the ground
  • Through wires (often ½-inch reinforcing bar) buried in the footings of buildings (UFER ground)
  • Buried grounding plates or rings
  • The frames of metal buildings (more common in commercial than residential construction)
  • The metal casings of private water supply wells

The illustration below shows the most common grounding electrodes used.

The Function and Importance of Earth Grounding System

A typical connection to a ground rod (although the part of the clamp in the foreground is installed backwards).

You will not be able to see the entire earth grounding system. However, there are a few things to look for, mostly around what’s missing or poorly connected.

In Part Two of this post, we take a look at common things that can go wrong with earth grounding systems and their solutions. See you at Part Two!


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