Cables Marking, NEC 310-11

(a) Required Information. 
All conductors and cables shall be marked to indicate the following information, using the applicable method described in (b) below. 

  1. The maximum rated voltage for which the conductor was listed.

  2. The proper type letter or letters for the type of wire or cable as specified elsewhere in this Code.

  3. The manufacturer's name, trademark, or other distinctive marking by which the organization responsible for the product can be readily identified.

  4. The AWG size or circular mil area. 

(b) Method of Marking. 

  1. Surface Marking. The following conductors and cables shall be durably marked on the surface. The AWG size or circular mil area shall be repeated at intervals not exceeding 24 in. (610 mm). All other markings shall be repeated at intervals not exceeding 40 in. (1.02 m). 
    a. Single- and multiconductor rubber- and thermoplastic-insulated wire and cable.
    b. Nonmetallic-sheathed cable.
    c. Service-entrance cable.
    d. Underground feeder and branch-circuit cable.
    e. Tray cable.
    f. Irrigation cable.
    g. Power-limited tray cable.
    h. Instrumentation tray cable. 

  2. Marker Tape. Metal-covered multiconductor cables shall employ a marker tape located within the cable and running for its complete length. 

    Exception No. 1: Mineral-insulated, metal-sheathed cable.
    Exception No. 2: Type AC cable.
    Exception No. 3: The information required in Section 310-11(a) shall be permitted to be durably marked on the outer nonmetallic covering of Type MC, ITC, or Type PLTC cables at intervals not exceeding 40 in. (1.02 m).
    Exception No. 4: The information required in Section 310-11(a) shall be permitted to be durably marked on a nonmetallic covering under the metallic sheath of Type ITC or PLTC cable at intervals not exceeding 40 in. (1.02 m). 

  3. Tag Marking. The following conductors and cables shall be marked by means of a printed tag attached to the coil, reel, or carton: 
    a. Mineral-insulated, metal-sheathed cable.
    b. Switchboard wires.
    c. Metal-covered, single-conductor cables.
    d. Conductors having outer surface of asbestos.
    e. Type AC cable. 

  4.  Optional Marking of Wire Size. The information required in (a)(4) above shall be permitted to be marked on the surface of the individual insulated conductors for the following multiconductor cables: 
    a. Type MC cable.
    b. Tray cable.
    c. Irrigation cable.
    d. Power-limited tray cable.
    e. Power-limited fire alarm cable.
    f. Instrumentation tray cable. 
    (c) Suffixes to Designate Number of Conductors. A type letter or letters used alone shall indicate a single insulated conductor. The following letter suffixes shall indicate the following: 

 
  • D -- For two insulated conductors laid parallel within an outer nonmetallic covering.
 
  • M -- For an assembly of two or more insulated conductors twisted spirally within an outer nonmetallic covering. 

    (d) Optional Markings. All conductors and cables contained in Chapter 3 shall be permitted to be surface marked to indicate special characteristics of the cable materials.