Equipment Grounding Conductor

DOE-HDBK-1092-2004

1) Arrangement to prevent objectionable current. Grounding of electrical systems, circuit

conductors, surge arresters, and conductive noncurrent-carrying materials and equipment

shall be installed and arranged in a manner that will prevent an objectionable current over

the grounding conductors or grounding paths. Use of a single-point grounding system, as

well as meeting the other requirements of NEC Article 250, will usually overcome problems.

2) Alterations to stop objectionable current. If the use of multiple grounding connections results

in an objectionable current, one or more of the following alterations are permitted to be

made, provided that the requirements of NEC 250.4(A)(5)(B)(4), are met. Such permitted

alterations are:

1. Discontinue one or more, but not all, of the grounding connections;

2. Change the locations of the grounding connections;

3. Interrupt the continuity of the conductor or conductive path interconnecting the grounding

connections; and/or

4. Take other suitable remedial action satisfactory to the authority having jurisdiction.

3) Temporary currents not classified as objectionable currents. Temporary currents resulting

from accidental conditions, such as ground-fault currents, that occur only while the

grounding conductors are performing their intended protective functions shall not be

classified as objectionable. This does not prohibit changes in the system to correct

excessive current during a fault condition.

4) Limitations to permissible alterations. The intent of NEC 250.6 is not to permit electronic

equipment to be operated on AC systems or branch circuits that are not grounded as

required by NEC Article 250. Currents that introduce noise or data errors in electronic

equipment are not considered to be the objectionable currents addressed in this Section.

Voltage differences and thus objectionable currents may exist because impedances to

ground are not equal throughout a grounding system due to variations of the resistance of

the earth, improper connections, or other problems.

Even though voltage differences allow unwanted currents to flow in the grounding

conductors, and induced noise may travel over this path, it is not to be used as a reason to

disconnect all grounding connections to any system component. At least one grounding

connection must remain.

9.3.2

EQUIPMENT GROUNDING CONDUCTOR

The equipment grounding conductor of a power-supply cord or interconnecting cable should be

size in accordance with NEC 250.122 and the associated NEC Table 250.122. The minimum

size equipment grounding conductor is based on the total rating of the enclosed equipments in

amperes. Note that the minimum size equipment grounding conductor may be smaller than the

size for the current-carrying conductors; i.e., the grounded (neutral) and ungrounded

conductors, which are sized per NEC Article 310.15 usually following NEC Table 310.16.

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