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There is a lot of confusion about grounding and bonding and the purpose of each. We talk about grounded electrical outlets, ungrounded outlets, ground rods, bonding, etc. Sometimes, the words “grounding” and “bonding” are used interchangeably, but they mean different things and they serve two different purposes. So, what is the difference between grounding and bonding? Let’s start with the definition of each one. Since I am a home inspector, I am going to discuss these terms only in regards to a home’s electrical system, and will not get into a discussion of the industrial uses of grounding and bonding.

What is Grounding?

Grounding is connecting your home’s electrical system to earth in a manner that will limit the voltage caused by lightning, line surges, or unintentional contact with higher-voltage lines, and that will stabilize the voltage to earth during normal operation.

Put another way, the purpose of grounding is to maintain a constant voltage of your home’s electrical system by dissipating voltage spikes caused by outside influences such as a lightning strike or a voltage spike on the transmission lines. The reason you don’t want voltage spikes on your home’s electrical system is because voltage spikes or surges can damage electrical equipment/components in your home.

 

Grounding is normally accomplished by connecting the electrical service of your home to a ground rod. This ground rod is normally an 8-foot long solid copper rod that is driven into the ground. This provides a path for any voltage spikes to travel to and dissipate into the ground.

ground rod

What is Bonding?

There are two different types of bonding to talk about here.
  1. The purpose of bonding is using a normally non-current-carrying conductor to connect devices together to keep them at the same voltage. An example of this is swimming pool equipment which must be electrically bonded together so that all equipment such as pumps and heaters will be at the same voltage. This will prevent possible electrocution in the event that someone was touching two different pieces of pool equipment at the same time if one of those pieces of equipment happened to be at a different voltage than the other. When they are properly bonded, they cannot be at different voltages.
  2. In regards to our home’s electrical system, bonding is creating a path for ground-fault current to travel back to the panel in order to clear the fault. Put another way, bonding provides a path for current to flow in order to trip a breaker if there is faulty or damaged equipment plugged in. This has been called grounding for many years. Most electricians and home inspectors call it grounding, but it is NOT grounding. Grounding is what I described above. Arguments will continue over what to call it. I am not here to debate that. For the purposes of this discussion, I will call it bonding which I believe more accurately describes what is truly happening.
breaker without ground wire
The concept of bonding electrical outlets may be easier to understand with an example. Let’s suppose that a wire comes loose inside your refrigerator. This is a live wire meaning it is energized to 120 volts. This live wire would shock and possibly kill someone if it is touched. Now, suppose that this loose wire inside the refrigerator is touching the frame or body of the refrigerator. This would cause the entire refrigerator to become energized, meaning that if you walked up to the fridge and touched it, you would be shocked or electrocuted.
Here’s where bonding comes into play – and here is where the two terms get confused and interchanged. In a home with a three-wire system, one of the three wires in the three-wire system is a bare ground wire. This bare ground wire can also be called the equipment grounding conductor (EGC). It is this ground wire that provides the bonding. Yes, it is confusing.
This bare wire, by way of the outlet and the refrigerator cord, is ultimately connected to the frame of the refrigerator. As soon as the live wire in the example above touches the frame of the refrigerator, a short circuit will result. This will create a high current traveling back to the electrical panel on that bare ground wire. This high current will cause the breaker that supplies power to the refrigerator to immediately trip and cut off power/voltage to the refrigerator. Now, if you touch the refrigerator, it will be completely de-energized and safe. This is how bonding protects people.
breaker tripping because of ground wire

What is the Difference Between Grounding and Bonding?

It should be clear that bonding and grounding are two totally different things.

Grounding is designed to protect your home’s electrical system and equipment from external stray voltages during normal operation.

 

Bonding is designed to protect people from normal voltages (and currents) when a problem exists with a piece of electrical equipment (such as the damaged refrigerator) in your home.

romex wire

What is a Two-Wire System?

On a two-wire system, you only have a hot and a neutral wire. There is no bare ground wire to provide ground fault protection. I’ve seen many homes where the homeowner has changed out their old, two-slotted outlets with new three-slotted outlets so that they can plug in things with three prongs. This gives a false sense of security since these three-slotted outlets are not actually grounded. In the example given above, if that hot wire comes loose and touches the refrigerator frame, there will be no ground wire for the high current to travel back to the panel and to trip the breaker. So, with a two-wire system (or in a three-wire system without the ground wire connected to the outlet), the frame of the refrigerator will remain energized and will remain an electrocution hazard to anyone who touches it.
two slotted outlet

Can You Ground Ungrounded Outlets by Adding a Ground Rod?

If I did a good enough job above explaining the difference between bonding and grounding, you will know that the answer to this question is NO. The two are almost completely unrelated. You can have a properly installed ground rod and not have any grounded outlets in your home. On the other hand, you can have all grounded outlets in your home without a ground rod. Again, grounding (ground rods) protect equipment, while grounded outlets (bonding) protects people.

How Much Current Will Flow Through a Ground Rod at 120 Volts?

One reason that ground rods cannot provide protection in the event of a ground-fault (such as the loose wire touching the refrigerator frame) is because the earth/soil/ground has too much resistance to allow sufficient current flow to cause a breaker to trip. Most breakers are in the 15 to 30-amp range, meaning that the current passing through the breaker must exceed the 15 to 30-amp rating of the breaker before the breaker will trip.
A grounding electrode conductor (GEC) is the wire that connects a home’s electrical system to the ground rod. I measured the resistance between the GEC on my home and the earth with an Earth Resistance Clamp – basically, a very sensitive and accurate ohm meter. As you can see in the photo, the resistance was 13.22 ohms.

Using Ohm’s law (voltage = current x resistance OR current = voltage ÷ resistance), I calculated that if I were to connect a 120-volt wire directly to my ground rod, nine amps would flow through the ground rod and into the ground (120 ÷ 13.22 = 9.08). Those nine amps would travel through that wire to the ground rod and be dissipated into the earth, and would continue to do so virtually forever. Nine amps will not cause a breaker to trip, but nine amps is much greater than the amount of current required to electrocute someone. Based on this, it should be obvious that a ground rod will not protect you from electrocution.

 

In summary, grounding and bonding can be confusing – especially since the terminology that has been used for years and continues to be used is confusing. Just remember that the purpose of grounding is to minimize the effect of voltage spikes caused by outside influences such as a lightning strike. The purpose of grounding is to protect equipment. Bonding on the other hand is used to clear ground faults by tripping breakers. Its purpose is to protect people.


Learn about grounded vs. ungrounded outlets.

© 2020 Mike Morgan

This article was co-written by Mike Morgan, owner of Morgan Inspection Services, and Kayla Perdue, Digital Marketing Manager. Morgan Inspection Services has been providing home, septic and well inspection services throughout the central Texas area since 2002. He can be reached at 325-998-4663 or at mike@morganinspectionservices.com. No article, or portion thereof, may be reproduced or copied without prior written consent of Mike Morgan.


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