Types of Grounding

Author: Stephen Frank

September 17th, 2022

Grounding is often one of the most misunderstood aspects of electrical systems. In this article we will explore the different types of grounding, the purpose of each, how they are different, and why it’s important to get it right.

Disclaimer: This article is for educational purposes only. Do not use or reference the information posted in this article as an alternative to official codes and standards.

Definitions

In the world of codes and standards it is common to start with the definitions. Clear understanding of definitions used to define technical terms is fundamental to proper interpretation and implementation.

Equipment Grounding Conductor (EGC): The conductive path(s) that provides a ground-fault current path and connects normally non–current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both.

Grounded Conductor: A system or circuit conductor that is intentionally grounded.

Grounding Electrode: A conducting object through which a direct connection to earth is established.

Grounding Electrode Conductor: A conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system.

Definitions obtained from 2021 NFPA 70E Standard for Electrical Safety in the Workplace

Equipment Grounding Conductor (EGC).

When most people think of an electrical ground they are thinking of the Equipment Grounding Conductor. It is more commonly referred to as ground, or the ground. It’s usually a bare copper cable or a small wire with green (green/yellow) insulation. For larger cables you’ll often see electricians identify them as EGC’s using green electrical tape just like in the photo above.

The National Electrical Code allows for more type of Equipment Grounding Conductors, but for this article we will be discussing the most common as mentioned above. Refer to NFPA 70 Article 250.118 if you wish to know the other types.

Two important things to remember about Equipment Grounding Conductors.

1. They help to minimize objectionable potential above ground on conductors and equipment enclosures by directly connecting equipment to ground (earth potential).

2. They provide an effective current path during a ground-fault to facilitate overcurrent device operation.

These are important points as it pertains to personnel and equipment safety. The Equipment Grounding Conductor is the primary reason why most people can safely go about their day touching and handling electrical appliances and equipment without the fear of getting shocked.

The most common misconception about EGC’s is that they carry current. They do not. These cables are not sized, nor are they intended to carry current under normal operations.

Equipment Grounding Conductors are most often sized using NFPA 70 Table 250.122.

Grounded Conductor

The second type of ground we will discuss is the Grounded Conductor and how it differs from the Equipment Grounding Conductor. The Grounded Conductor is more often than not the system neutral, and therefore it is most commonly referred to as such. The Grounded Conductor typically has white/gray insulation, or for larger cables has been identified using white electrical tape such as in the image above.

The primary difference between the Grounded Conductor and the Equipment Grounding Conductor (EGC) is that the Grounded Conductor is intended to carry current during normal operations.

The amount of current on the Grounded Conductor can range from very little (in a perfectly balanced three-phase system), to full load current such as in a single-phase 120 VAC system with only one load.

As we stated in the definitions, the Grounded Conductor is a conductor that has been intentionally grounded. This process is call Bonding. How and where the bonding occurs is another complicated and important topic, which we will discuss in a future blog post.

The most common misconception for Grounded Conductors regards bonding and the false belief that you can “bond the neutral to ground” as many times as you want or at any point in the system. This is not only false, but dangerous.

Grounded Conductors are most often sized using NFPA 70 Table 250.102(C)(1)

Notice how the Grounded Conductor is sized based on the size of the current carrying conductors, whereas the Equipment Grounding Conductor is sized based on the rating of the overcurrent protection device. Grounded Conductors are more often than not larger than the associated Equipment Grounding Conductors. They need to be because they are intended to carry current. However, it is not uncommon to see installations where both have been oversized intentionally to the point that they are the same size as the current carrying conductors. This is often done simply out of convenience for the person ordering the material or performing the installation.

Grounding Electrode

The Grounding Electrode is the object used to establish a direct connection with the earth. When we refer to earth in regards to electrical systems, we are talking about Ground. If you look up the definition for Ground in the NFPA 70 is simply says “the earth”. So yes, we are talking about the physical dirt.

This is often a long rod (~10 feet) that is physically driven into the dirt, and you’ll sometimes see the top portion of the rod sticking out of the ground like in the photo above. It can also be an underground network of cables and rods in a grid pattern, commonly referred to as the grounding grid. This will be invisible to the observer once backfilled with dirt, except for maybe some exposed cables sticking out of the ground, which are generally referred to as pigtails. These pigtails are in fact the Grounding Electrode Conductors, which we will cover in the next section below.

The primary purpose of the Grounding Electrode is to maintain the electrical equipment at earth potential (assumed to be 0 Volts).

Another purpose is to dissipate over voltage conditions into the earth. An over voltage condition can occur if a high-voltage system accidentally connects to a low-voltage system. It can also occur by lightning strikes.

A common misconception is that the Grounding Electrode system, or the grounding grid, can be used in place of, or as an alternative to an Equipment Grounding Conductor. This is false, and also dangerous. The earth itself is not considered a suitable conductor for clearing ground faults. The following video is a great demonstration of what happens when the earth is used to clear a ground fault in the absence of an appropriate EGC.

Grounding Electrode Conductor

Lastly, we have the Grounding Electrode Conductor. This one is relatively straight forward compared to the others. It is simply the cable that connects the system Grounded Conductor, the Equipment Grounded Conductor, or both to the Grounding Electrode.

In the image from the previous section you can see the Grounding Electrode Conductor. It is the cable connecting the ground rod in the earth to the ground bar in the enclosure. It could also be the pigtails that we referred to in the previous section.

The common misconception with the Grounding Electrode Conductor is the same as with the Grounding Electrode in that it can be used in place of, or as an alternative to an Equipment Grounding Conductor. This is also false for the same reasons state above.

Conclusion

Instead of a long summary I would instead like to conclude this article with a simple sketch that I created to help me teach grounding and bonding during my training sessions.

The sketch shows a basic low-voltage distribution setup from the transformer to the load with the focus on defining the different types of connections per the NFPA 70 National Electrical Code.