250.121 Use of Equipment Grounding Conductors.

Although not that commonly done, the equipment grounding conductor can also serve as a grounding electrode conductor if it meets all the requirements for both conductors. This conductor would need to be continuous, without a splice per 250.64(C).
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Although not that commonly done, the equipment grounding conductor can also serve as a grounding electrode conductor if it meets all the requirements for both conductors. This conductor would need to be continuous, without a splice per 250.64(C).

Equipment grounding conductors (EGC’s) serve to provide a ground-fault current path by connecting normally non-current carrying metal enclosures of electrical equipment to the system grounded conductor or the grounding electrode conductor or both (see Article 100 definition of Grounding Conductor, Equipment).

A grounding electrode conductor (GEC) connects the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system (see Article 100 definition of Grounding Electrode Conductor).

Each of these are sized completely different. EGC’s are sized from Table 250.122 based on the size of the overcurrent device ahead of the circuit. The GEC is sized from Table 250.66 based on the size of the ungrounded service entrance conductors.

Section 250.121 allows one conductor to serve both purposes as long as it does not carry any objectionable current in accordance with 250.6(A) and meets all of the requirements for both an EGC and GEC.

Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC® edition of NFPA 70.

2020 Code Language:

250.121(A) Grounding Electrode Conductor.

An equipment grounding conductor shall not be used as a grounding electrode conductor.

Exception: A wire-type equipment grounding conductor installed in compliance with 250.6(A) and the applicable requirements for both the equipment grounding conductor and the grounding electrode conductor in Parts II, III, and VI of this article shall be permitted to serve as both an equipment grounding conductor and a grounding electrode conductor.

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250.121 Use of Equipment Grounding Conductors.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Which of the following is true of a wire type equipment grounding conductor?

A: It is never permitted to also serve as a grounding electrode conductor.
B: It can also be used as a grounding electrode conductor if it does not carry any objectionable current and meets all of the requirements for both an EGC and GEC.
C: It is sized from Table 250.66.
D: It is sized from Table 250.102(C)(1).
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