What is grounding and what is bonding? There is a lot of misinformation out there. Many of the DIY and instructional videos/websites have no clue about the purpose of grounding and/or bonding, providing faulty instructions which can lead to injuries or in severe cases, death. In addition, many practicing electricians and engineers do not understand the full concepts of grounding and/or bonding. ANSI/NFPA 70, National Electrical Code Section 250.4(A) Grounded Systems and Section 250.4(B) Ungrounded Systems performs a great service to the industry by defining specific “prescriptive methods” necessary to install safe and effective grounding and bonding. Let us understand the basics of these terms and how they play a part in electrical safety.
The NEC, National Electrical Code, NFPA 70 defines:
- Ground: The Earth. (CMP-5), [NFPA 70-2023]
- Grounded (Grounding): Connected (connecting) to ground or to a conductive body that extends the ground connection. (CMP-5), [NFPA 70-2023]
- Bonded (Bonding): Connected to establish electrical continuity and conductivity. (CMP-5), [NFPA 70-2023]
- Bonding: An electrical connection between an electrically conductive object and a component of a lightning protection system that is intended to significantly reduce potential differences created by lightning currents. [NFPA 780-2023]
- Grounded Conductor: A system or circuit conductor that is intentionally grounded. (CMP-5), [NFPA 70-2023] Informational Note: Although an equipment grounding conductor is grounded, it is not considered a grounded conductor.
- Grounding Conductor, Equipment (EGC). A conductive path(s) that is part of an effective 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. (CMP-5), [NFPA 70-2023] Informational Note: It is recognized that the equipment grounding conductor also performs bonding.
Essentially, we ground to limit the voltage imposed by lighting, line surges, or unintentional contact with higher-voltage lines and to stabilize the voltage to earth during normal operation. We bond to provide an effective low impedance ground-fault current path. In the case of lighting protection, we bond to significantly reduce potential differences created by lighting currents.
The Equipment Grounding Conductor (EGC) plays a vital role in keeping us safe from electric shock. The EGC is used to bond all components together to the source in a manner that establishes an effective, low impedance ground-fault current path, in turn protecting us. Why does an EGC work? The current must travel back to the source. We have all been taught that a current is like water, and it will take the easiest path back to the source.
THAT ASSUMPTION IS FALSE! The current does not take the easiest path back to the source. THE CURRENT TAKES EVERY AVAILABLE PATH BACK TO THE SOURCE. Current division is inversely proportional to the branch circuit resistance. The current does not try to get to the ground, the current is trying to get back to the source.
The idea behind the EGC is twofold:
- To provide a low enough impedance path to allow sufficient current to flow to trip the circuit breaker or open the fuse.
- The EGC impedance is low enough to shunt almost all the current around the person or persons to prevent a shock or an electrocution.
Another myth in the electrical world is that there is such thing as a safety ground (rod). There is no such thing because the earth (soil) does not have sufficiently low resistance to establish a low impedance fault current path. The NEC states “The earth shall not be considered as an effective ground-fault current path.” The term “Safety Ground Rod” gets thrown around a lot in the airfield lighting industry with the intention of protecting airfield lighting maintenance personnel. There is nothing further from the truth, a ground rod at each light base does nothing to enhance the safety of an airfield lighting maintenance person, however the ground rod is a key component of an effective lightning protection system.
Safety is always the number one priority when working on any project. Differences between fact and fiction can quite literally be a life-or-death matter with electrical work.
Additional recommended resources:
- Free materials from Mike Holt’s Bonding and Grounding Program Bonding and Grounding (mikeholt.com)
- IEAE Magazine article: Are Your Street Lights Grounded? https://iaeimagazine.org/magazine/2011/november2011/are-your-streetlights-grounded/
Carl Johnson II, ACE
Senior Aviation Lighting Specialist
Mr. Johnson has fifty plus years of design, construction, and maintenance of electrical distribution systems, airfield lighting and NAVAID systems experience. For the last thirty-five years, Carl’s primary focus has been the design, construction and maintenance of airfield lighting and NAVAID systems. He is a Licensed Florida Certified Electrical Contractor and is an AAAE Airport Certified Employee (ACE) in Airfield Lighting Maintenance. Carl has provided expert testimony on the state of airfield lighting practice and safety during project mediation and litigation. Carl is knowledgeable of NFPA, NEC, FAA, IEEE, and military standards. He is a Principal Member of the NFPA 780 Technical Committee for Lightning Protection, UL STP 96 which covers activity for UL 96 and UL 96A Standards, and he serves on the IES Subcommittee for RP-37, Outdoor Lighting for Airport Environments.