Ecmweb 23877 20190214 Codeqa 250 4a5 01 1024
Ecmweb 23877 20190214 Codeqa 250 4a5 01 1024
Ecmweb 23877 20190214 Codeqa 250 4a5 01 1024
Ecmweb 23877 20190214 Codeqa 250 4a5 01 1024
Ecmweb 23877 20190214 Codeqa 250 4a5 01 1024

Code Q&A: Effective Ground-Fault Current Path

Feb. 13, 2019
Check your knowledge of ground-fault current and its path to ground.

Q. What does the Code mean by an “Effective Ground-Fault Current Path”?

See the answer below.

This answer is based on the 2017 NEC.

A. The effective ground-fault current path is made by bonding together the metal parts of electrical raceways, cables, enclosures, and equipment and to the supply source in a manner that creates a low‑impedance path for ground‑fault current to flow, which facilitates the operation of the circuit overcurrent protection device [Sec. 250.4(A)(5)]. (Fig. 1)

To ensure a low‑impedance ground‑fault current path, all circuit conductors must be grouped together in the same raceway, cable, or trench [300.3(B), 300.5(I) and 300.20(A)].

Because the earth isn’t a low impedance path for fault current, it isn’t suitable to serve as the required effective ground‑fault current path. Therefore, an equipment grounding conductor (EGC) of a type recognized in Sec. 250.118 is required to be installed with all circuits.

Let’s run through an example problem to prove this point.

What’s the maximum fault current that can flow through the earth to the power supply from a 120V ground fault to metal parts of a light pole without an EGC that’s grounded (connected to the earth) via a rod having a contact resistance to the earth of 25 ohms?

Solution:

I = E ÷ R

I = 120V ÷ 25 ohms = 4.80A

DANGER: Because the contact resistance of an electrode to the earth is so high, very little fault current returns to the power supply if the earth is the only fault current return path.  Result — the circuit overcurrent protection device won’t open and all metal parts associated with the electrical installation, metal piping, and structural building steel will become and remain energized (Fig. 2).

These materials are provided to us by Mike Holt Enterprises in Leesburg, Fla. To view Code training materials offered by the company, visit www.mikeholt.com/code.

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.

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