Section 250.119 describes the ways an equipment grounding conductor must be identified. Equipment grounding conductors can be bare, covered or insulated. Individually covered or insulated equipment grounding conductors must have a continuous outer finish that is either green, or green with one or more yellow stripes except as permitted elsewhere in section 250.119.

The general rule is that equipment grounding conductors 6 AWG and smaller are required to be green their entire length. Equipment grounding conductors 4 AWG and larger are NOT required to be green their entire length.

For example, a 4 AWG black wire can be used as an equipment grounding conductor and have green tape applied at each end and inside all accessible locations such as junction boxes.

According to NEC^® 250.119(A)(2), when reidentifying a 4 AWG or larger equipment grounding conductor that is not green for its entire length, the identification method must encircle the conductor and must be accomplished by one of the following:

1. Stripping the insulation or covering from the entire exposed length
2. Coloring the insulation or covering green at the termination
3. Marking the insulation or covering with green tape or green adhesive labels at the termination

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:

250.119 Identification of Equipment Grounding Conductors.

Unless required elsewhere in this Code, equipment grounding conductors shall be permitted to be bare, covered, or insulated. Individually covered or insulated equipment grounding conductors shall have a continuous outer finish that is either green or green with one or more yellow stripes except as permitted in this section. Conductors with insulation or individual covering that is green, green with one or more yellow stripes, or otherwise identified as permitted by this section shall not be used for ungrounded or grounded circuit conductors.

Exception No. 1: Power-limited Class 2 or Class 3 cables, power-limited fire alarm cables, or communications cables containing only circuits operating at less than 50 volts ac or 60 volts dc where connected to equipment not required to be grounded shall be permitted to use a conductor with green insulation or green with one or more yellow stripes for other than equipment grounding purposes.

Exception No. 2: Flexible cords having an integral insulation and jacket without an equipment grounding conductor shall be permitted to have a continuous outer finish that is green.

Informational Note: An example of a flexible cord with integral-type insulation is Type SPT-2, 2 conductor.

Exception No. 3: Conductors with green insulation shall be permitted to be used as ungrounded signal conductors where installed between the output terminations of traffıc signal control and traffıc signal indicating heads. Signaling circuits installed in accordance with this exception shall include an equipment grounding conductor in accordance with 250.118. Wire-type equipment grounding conductors shall be bare or have insulation or covering that is green with one or more yellow stripes.

(A) Conductors 4 AWG and Larger. Equipment grounding conductors 4 AWG and larger shall comply with 250.119(A)(1) and (A)(2).

(1) An insulated or covered conductor 4 AWG and larger shall be permitted, at the time of installation, to be permanently identified as an equipment grounding conductor at each end and at every point where the conductor is accessible.

Exception: Conductors 4 AWG and larger shall not be required to be marked in conduit bodies that contain no splices or unused hubs.

(2) Identification shall encircle the conductor and shall be accomplished by one of the following:

1. Stripping the insulation or covering from the entire exposed length
2. Coloring the insulation or covering green at the termination
3. Marking the insulation or covering with green tape or green adhesive labels at the termination

(B) Multiconductor Cable. One or more insulated conductors in a multiconductor cable, at the time of installation, shall be permitted to be permanently identified as equipment grounding conductors at each end and at every point where the conductors are accessible by one of the following means:

(1) Stripping the insulation from the entire exposed length.

(2 )Coloring the exposed insulation green.

(3) Marking the exposed insulation with green tape or green adhesive labels. Identification shall encircle the conductor.

(C) Flexible Cord. Equipment grounding conductors in flexible cords shall be insulated and shall have a continuous outer finish that is either green or green with one or more yellow stripes.