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Grounding & bonding

Navigating the grounding and bonding of electrical systems can be a tall task unless you have taken the time to familiarize yourself with the requirements of Article 250 of NFPA 70®, National Electrical Code® (NEC®).

Where should you start? The following are some common questions from individuals who are just beginning to explore Article 250. However, beyond beginners, this information can also be useful for experienced installers that want to know more about why they do what they have been trained to do and whether they have been trained to do it properly.


1. Are grounding and bonding the same thing?

Article 250 of the NEC covers the grounding and bonding of electrical systems. By definition, as well as by function, grounding and bonding are not the same thing. However, they do work closely together in a yin and yang relationship to help ensure safety in electrical systems.

2. What is grounding?

Grounding is the electrical system’s connection to the ground itself. Article 100 of the NEC defines ground as “the earth.” Section 250.4(A)(1) states that grounded electrical systems “shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.”

3. What is bonding?

Article 100 of the NEC defines bonded (bonding) as “connected to establish electrical continuity and conductivity.” Bonding metal parts, such as enclosures and raceways, ensures that they are all continuous on an effective ground-fault current path (EGFCP) that references back to ground (earth). The EGFCP helps operate devices such as circuit breakers and fuses or ground-fault detectors in ungrounded systems. 

In grounded systems, it is important to bond the equipment grounding conductors to the system grounded conductor to complete the EGFCP back to the source of electricity. The conductivity of the EGFCP is critical for protective devices to work properly. This speaks to why we scrape the paint from contact surfaces of metallic enclosures to make our electrical system bonding connections. Removing the paint, as required in Section 250.12, provides for a better connection and conductivity path. 

In the 2020 edition of the NEC, the language “or bonded” was added to Section 250.12, which now reads “Nonconductive coatings … on equipment to be grounded or bonded shall be removed …” This further emphasizes that grounding and bonding are not the same but work together to ensure the safety of the electrical system.

4. Why is it so important to ensure you have proper grounding and bonding for your electrical system?

First and foremost is the safety of personnel within a building. Ensuring the proper grounding and bonding of the electrical system could very well be the reason an employee within the building avoids an unintended shock and can go home that night. It is that important. 

Other items that could be negatively affected by improper grounding and bonding are sensitive equipment and low-voltage signals. Although these items could be tied to safety, their functionality is also critical to production. How would management react if an improper grounding and bonding installation negatively impacted their production goals? 

5. What is the goal of the NEC requirements for grounding and bonding?

Section 250.4 states the general requirements for grounding and bonding of electrical systems for both grounded and ungrounded systems. For grounded systems, the NEC requires you to perform all of the following: electrical system grounding, electrical equipment grounding, electrical equipment bonding, and bonding of electrically conductive materials. In ungrounded systems, the same actions are required except for electrical system grounding. When these NEC requirements are implemented, an effective ground-fault current path is created, which is your desired end goal. 

By definition, an effective ground-fault current path (EGFCP) is an intentionally constructed, low-impedance, electrically conductive path designed and intended to carry current under ground-fault conditions from the point of a ground fault to the electrical supply source. A well-designed EGFCP can help remove dangerous voltage from unintended faults by allowing overcurrent protective devices, such as circuit breakers and fuses, to properly sense a fault and open the circuit.

6. What sections of the NEC should you be well-versed in to ensure you perform the grounding and bonding of the electrical system correctly?

Article 250 is a foundational pillar of the NEC; it should be studied in its entirety to make sure that both grounding and bonding are done properly. A few critical resources that you should use regularly are Tables 250.66, 250.102(C)(1), and 250.122. These tables help you properly size wiring for the grounding and bonding of your electrical system. Becoming familiar with the proper use of these tables can help installers ensure proper grounding and bonding on their projects and, in turn, ensure the safety of those within the building.