April, 2015
Fundamentals
Inspection News and Views from the American Society of Home Inspectors



Earth Grounding System

ANDY TRAN

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.

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.

Connects Service Box to 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 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 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 away safely unexpected electrical charges from other sources. 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.

Ground Wires / Earth Ground Conductors

Ground wires are typically copper and maybe bare or insulated. They are typically 8-gauge for 100-amp service and 6-gauge for 200-amp service. It is best practice to avoid splices in a ground wire since every splice is a potential poor connection. (refer to image at top of page)

Where does the grounding system end?

The goal is to get the electricity to flow to ground. This is done by connecting the earth ground wire to a grounding electrode.

There are several ways to do this, including

  1. through metal water supply pipes
  2. through metal rods driven into the ground.
  3. through wires (often ½-inch reinforcing bar) buried in the footings of buildings (UFER ground)
  4. buried grounding plates or rings
  5. the frames of metal buildings (more common in commercial than residential construction)
  6. the metal casings of private water supply wells

Figure 2 below shows the most common grounding electrodes used.

A typical connection to a ground rod

Let’s look at what goes wrong with earth grounding systems. The implications are the same throughout. An ineffective or missing earth grounding system cannot perform its safety functions. There is greater risk of electrical shock, fire and equipment damage in houses where the earth grounding system is not effective.

  1. No grounding
  2. Ground wire attached to plastic pipe
  3. Ground wire after (downstream of) meters and valves, with no jumper
  4. Spliced ground wire
  5. Ground wire attached to abandoned pipe
  6. Poor connections
  7. Ground connections not accessible
  8. Ground rod cut off
  9. Corroded ground wire
  10. Undersized ground wire

We’ll discuss three of the most common conditions with earth grounding systems

No Grounding

A missing earth grounding conductor (wire) is the result of improper installation. If it is missing, this is a serious electrical defect and inspectors should recommend immediate improvements. Clients, real estate agents and existing homeowners may have a tough time understanding how this is important since the house has been operating this way for a long time. Explain that this is an emergency safety device and houses can operate for years without it, but the one time they need it, they won’t have the protection they should. Is it worth risking someone’s life? The good news is that it is typically not an expensive improvement.

There is no ground wire coming out of the main disconnect part of this panel.

Ground Wire Downstream of Meters and Valves With no Jumper

We talked earlier about how meters, valves and dielectric connectors could interrupt electrical continuity. This is the result of poor original installation or plumbing changeovers.

Make sure the ground wire is connected as close as possible to the plumbing service entry and upstream of (before) any devices that might interrupt it. Where there are devices such as meters upstream, a jumper should be added around the devices or the ground wire should be moved upstream of these. The jumper should be the same size as the ground wire and clamped securely to the metal pipe.

Metal natural gas piping must be bonded to the grounding system. This applies to new installations or updates involving gas piping or electrical service work. It is common to find this bonding wire connected to the plumbing system at the water heater, where the gas and water pipes are close together. In this case, a jumper should be provided around the water meter to maintain continuity of bonding for the gas piping (although the electrical system may be properly grounded without this jumper).

Loose or Poor Connections

Loose or poor connections are caused by:

  1. poor installation
  2. vibration
  3. corrosion

The ground wire (earth grounding electrode) is typically connected to the service box at one end and to a pipe and/or ground rod(s) at the other. Make sure the wire is securely fastened at both ends. Where ground wires are attached to pipes, it’s not adequate to just wrap the wire around the pipe. The wire must be secured with a clamp approved for that purpose.

The wire should be tight in the clamp and the clamp should be tight on the pipe. Corrosion of the wire, clamp or pipe can result in poor connections. Where you see this, recommend further investigation or improvement as appropriate.

Summary

We have introduced earth grounding systems in this discussion and touched on some of the common issues. More information regarding other conditions, their causes, implications and strategies for inspection can be found in the ASHI@HOME training program.