Grounding: Understanding the Essentials for Building the Foundation of a Structure’s Electrical System
Grounding is a term an electrician, electrical engineer, or facility manager is very familiar with and uses frequently, but what does it mean? The initial thought is, it’s just connecting a grounding conductor to the earth. In simple terms that is correct, but it is more than that. First, we must understand what grounding is so a proper grounding system can be established.
Grounded or grounding, as defined in the 2020 edition of NFPA 70®, National Electrical Code® (NEC®), Art. 100, is connecting to ground or to a conductive body that extends the ground connection. So, I’m sure many of you are thinking, just stick a wire in the ground and call it good, right? Not exactly. There first must be an effective ground-fault current path created to ensure a safe electrical system. Basically, it is the creation of a low-impedance electrically conductive path that facilitates the operation of the overcurrent protective device. This path must be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the electrical wiring system where a ground fault may occur. The earth itself is not considered an effective ground-fault current path, so sticking the wire in the ground is not enough.
Grounding is the very foundation of a building or structure’s electrical system. According to 250.20(B) of the 2020 NEC alternating-current (AC) systems of 50 volts to 1000 volts must be grounded which means referenced to earth. This is accomplished through a properly installed grounding electrode system. Having a strong grounding electrode system stabilizes voltage and helps to clear ground faults. The 2020 NEC, Section 250.50 gives the outline of a grounding electrode system and section 250.52 lists the approved grounding electrodes. A few of the more efficient grounding electrodes for buildings and structures are:
- Metal Underground Water Pipe
- Metal In-ground Support Structures
- Concrete-Encased Electrode (also known as “footer ground” or “Ufer ground”).
- Ground Ring
A grounding electrode system is the connection to earth, through the code required grounding electrodes. The grounding electrodes then get connected back to the building’s electrical service via a grounding electrode conductor (GEC). The GEC, at the building or structure’s service, is terminated on the neutral bar within the electrical service equipment alongside the grounded (neutral) conductor. The neutral bar is bonded (connected) to the service equipment enclosure through a main bonding jumper which in turn creates an effective ground-fault current path for the electrical system.
But once an effective ground-fault current path has been established to the earth, then what? How is the electrical equipment found in buildings and structures going to be grounded? It’s through the branch circuit equipment grounding conductor (EGC). EGCs come in various sizes, types, and materials as found in the 2020 NEC, Section 250.118. Some of those are:
- Copper, aluminum, or copper-clad aluminum conductors
- Rigid metal conduit (RMC)
- Intermediate metal conduit (IMC)
- Electrical metallic tubing (EMT)
Frequently, EGCs are the raceway system, RMC, IMC, or EMT. These types of EGCs are bonded together and to the equipment enclosure through a series of listed set screw or compression couplings and connectors. Most connectors utilize lock nuts or bond bushings for the connection to the electrical equipment or enclosures. Where bond bushings are used, they require an additional conductor, referred to as an equipment bonding jumper, which is required to finish the connection to the enclosure, neutral bar, or EGC bar. This helps complete the effective ground-fault current path. Using a bond bushing with equipment bonding jumpers can be more prone to human error or mechanical failure, therefore, the effective-ground-fault current path may not be as sound. EGCs that are an electrical conductor such as copper, aluminum, or copper-clad aluminum conductors, can be more effective due to the direct connection to the electrical equipment, enclosure, neutral bar or EGC bar. Opportunity for failure is less with this type of EGC because of the reduced connection points.
In general, when installing an EGC, the approved EGC shall be contained within the same raceway, trench, cable, or cord from the electrical service or sub-panel as the feeder or branch circuit conductors that provide power to the electrical equipment. From an electrical safety standpoint and looking at NFPA 70E®, Standard for Electrical Safety in the Workplace®, Section 120.5(8), where there is a possibility of induced voltages, all circuit conductors and circuit parts should be grounded before touching them. This is one of the potential steps for establishing an electrically safe work condition (ESWC), so a weak or non-functioning EGC would make it difficult or impossible to create an ESWC when the need for replacing or maintaining the electrical equipment arises.
To learn more about proper bonding, take a deeper look at Art. 250 of the 2020 NEC. Our newest grounding and bonding fact sheet will also be a helpful resource. Download it here.
Failure to establish an effective ground-fault current path through proper grounding may prevent overcurrent protective devices from working properly and therefore not effectively clearing a ground-fault, which could result in a shock, electrocution, or arc flash incident. By creating the effective ground-fault current path you’ll not only be doing the job correctly, but you’ll keep yourself and others safe to boot.
NFPA 70 the National Electrical Code® (NEC®) is now available in NFPA LiNK™, the association’s information delivery platform with NFPA codes and standards, supplementary content, and visual aids for building, electrical, and life safety professionals and practitioners. Learn more at nfpa.org/LiNK.