Low Voltage UL/NEC Power and Control Cable and Wire Technical Requirements

This article is about Technical Requirements of Low Voltage UL/NEC Power and Control Cable and Wire of Electrical Power System as per International Codes and standards for Commercial Buildings, Plants and Refinery Projects and article is written for engineers, technical managers, supervisors and technicians.

Low Voltage UL/NEC Power and Control Cable and Wire

Low Voltage Power and Control Cable Ratings

  1. Ratings – Cable and wire shall be rated 600 V.
  2. Ratings – Cable and wire shall have a minimum temperature rating of 90°C dry locations and 75°C for wet locations.

Low Voltage Power and Control Cable Construction

  1. Construction and Certification – Cable and wire shall conform to UL standards according to the particular cable type (e.g., UL 1277, including its vertical tray flame test, for type TC tray cables, etc.).
  2. Construction – Single- or multi-conductor cable with concentric neutral wire, metallic armor, and/or metallic sheaths shall be protected with a PVC (or equivalent) jacket.
  3. Construction – Cable and wire conductors shall be certified copper alloy in accordance with material specifications referenced in ASTM B8 or ASTM B496.
  4. Construction – Cable and wire for industrial locations shall be stranded (regardless of size). Mineral insulated cables and specialty cables (e.g., down hole pump motor cables, high temperature cables, etc.) with solid conductors are also permitted.
  5. Construction – Cable and wire conductors with cross-section-area larger than 6 mm² (10 AWG) shall be stranded (regardless of location). Mineral insulated cables and specialty cables (e.g., down hole pump motor cables, high temperature cables, etc.) with solid conductors are also permitted.
  6. Construction – Stranded cable and wire shall have stranding in accordance with ASTM B8 (Class B or Class C) or ASTM B496; except flexible cords, portable cables, battery leads and motor leads may have finer stranding in accordance with appropriate UL Standards or the manufacturers’ recommendations.
  7. Conductor Identification – Control cables shall be numbered or color-coded by conductor colors other than green, green with yellow stripes, white, or gray.
  8. Construction – Control conductor cross-sectional-area shall be 2.5 mm² (14 AWG), or larger. (Table-1)
  9. Construction – Power conductor cross-sectional-area shall be 4 mm² (12 AWG), or larger. (Table-1).
  10. Construction – Cable intended for underground service to security lighting shall be PVC-jacketed Type AC (armored) or Type MC (metal-clad) cable.
  11. Construction – Cable intended for installation in classified hazardous locations shall contain either (a) an insulated stranded copper equipment grounding conductor, or (b) be NEC Type MC cable with a steel cable armor approved for use as an equipment grounding conductor (within the PVC jacket of the cable).
  12. Construction – Cable shall include an insulated copper equipment grounding conductor if either (a) the project’s cable tray and raceway system is not approved for use as an equipment grounding conductor, or (b) the project’s cable tray system does not contain a separate copper equipment ground conductor.

UL Wire and Cable Marking Guide

  1. Marking – Cable and wire shall be externally marked by the manufacturer to indicate the following information –
    1. Maximum rated voltage (“”600 V”” or “”600 volts””).
    2. Type letters for the cable and/or wire, as specified in UL and NFPA 70 NEC (e.g., TC, MC, CS, ALS, AC, UF, USE, THHN-2 THWN-2, XHHW-2, etc.).
    3. Manufacturer’s name, trademark, or other distinctive marking.
    4. M/C Cable – quantity and size (AWG, KCM, or mm2 cross-sectional area) of conductors.
    5. Cables with a neutral conductor that is smaller than ungrounded conductors (NFPA 70, NEC 310.11(A))”.
  2. Cable Marking – The following cable types shall be durably marked on the surface. The AWG size or circular mil area shall be repeated at intervals not exceeding 610 mm (24 in.). All other markings shall be repeated at intervals not exceeding 1.0 m (40 in.).
    1. Rubber- and thermoplastic-insulated / jacketed cable
    2. Nonmetallic-sheathed cable (Types NM, NMC, and NMS)
    3. Service-entrance cable (Types USE and SE)
    4. Underground feeder and branch-circuit cable (Type UF)
    5. Tray cable (Type TC)
    6. Irrigation cable (NEC Art 675.4)
    7. Power-limited tray cable (Type PLTC)
    8. Instrumentation tray cable (NFPA 70, NEC 310.11(B)(1))
  3. Cable Marking – The following cable type shall be marked by means of a printed tag attached to the coil, reel, or carton:
    1. Mineral-Insulated (Type MI) metal-sheathed cable.
    2. Switchboard wires.
    3. Metal-covered, single-conductor cables.
    4. Type AC cable (NFPA 70, NEC 310.11(B)(3))”.

Low Voltage Cable and Wire Identification as per UL & NEC Standard

  1. Conductor Identification – Insulated or covered Grounded Conductors (Neutral) 6 AWG or smaller shall be identified by (a) continuous white or gray outer finish, (b) by three continuous white stripes on other than green insulation along its entire length, or (c) by distinctive marking at its terminations at the time of installation for mineral-insulated (Type MI) cable or other specialty high-temperature cables. NFPA 70, NEC 310.12(A) and 200.6)
  2. Conductor Identification – Insulated or covered Grounded Conductors (Neutral) larger than 6 AWG shall be identified by (a) continuous white or gray outer finish, (b) by three continuous white stripes on other than green insulation along its entire length, or (c) by distinctive marking at its terminations at the time of installation. This marking shall encircle the conductor or insulation. (NFPA 70, NEC 310.12.(A) and 200.6)
  3. Conductor Identification for Projects with both 480/277 and 208/120 VAC four-wire systems – Cables with an insulated or covered Grounded Conductor (Neutral) shall have an outer covering of white with a readily distinguishable, different colored stripe other than green running along the insulation, or shall have other and different means of identification as allowed by NEC 200.6 and approved to distinguish each system’s grounded conductor. (NFPA 70, NEC 310.12.(A) and 200.6(D))
  4. Conductor Identification – Grounding Conductors (EGC or Bonding) shall be either bare, covered, or insulated. If individually covered or insulated, then EGC’s shall (a) have a continuous outer finish that is solid green, (b) continuous green finish with one or more yellow stripes, (c) stripped to bare copper where exposed, (d) colored (dyed or painted) green where exposed, or (e) marked green with tape or adhesive labels where exposed.
    (NFPA 70, NEC 310.12(B) and 250.119″
  5. Conductor Identification – Ungrounded Conductors (Phase Conductors, Pole Conductors, or Signal Conductors) shall be insulated and finished to be clearly distinguishable from grounded and grounding conductors. Distinguishing markings shall not conflict in any manner with the required cable identification markings. NFPA 70, NEC 310.12(C)
  6. Conductor Construction – Cables and conductors shall comply with the applicable provisions of NEC Table 310.13(A), including insulation identification, materials, and thickness . (NFPA 70, NEC 310.13)
  7. (A) Dry Locations. Insulated conductors and cables used in dry locations shall be any of the types identified in this Code.
    (B) Dry and Damp Locations. Insulated conductors and cables used in dry and damp locations shall be Types FEP, FEPB, MTW, PFA, RHH, RHW, RHW-2, SA, THHN, THW, THW-2, THHW, THHW-2, THWN, THWN-2, TW, XHH, XHHW, XHHW-2, Z, or ZW.
    (C) Wet Locations. Insulated conductors and cables used in wet locations shall be
    (1) Moisture-impervious metal-sheathed;
    (2) Types MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THHW-2, THWN, THWN-2, XHHW, XHHW-2, ZW; or
    (3) Of a type listed for use in wet locations.
    (D) Locations Exposed to Direct Sunlight. Insulated conductors and cables used where exposed to direct rays of the sun shall be of a type listed for sunlight resistance or listed and marked “sunlight resistant.
  8. 310.9 Corrosive Conditions.
    Conductors exposed to oils, greases, vapors, gases, fumes, liquids, or other substances having a deleterious effect on the conductor or insulation shall be of a type suitable for the application. (NFPA 70, NEC 310.8).

International Standard and Codes for Low Voltage UL/NEC

  1. Non-Hazardous Indoor Enclosures, Installation and Pre-Commissioning
  2. Boxes, Enclosures, and Accessories Materials Selection & Requirements
  3. SAES-J-902 — Electrical Systems for Instrumentation.
  4. SAES-J-601 — Emergency Shutdown and Isolation Systems.
  5. NFPA 70 National Electrical Code (NEC), 2008 Edition
  6. SAES-P-104 Wiring Methods and Materials, 13 January 2008
  7. SAES-P-111 Grounding, 16 July 2006
  8. Manufacturer’s Instructions – Power Cable Manual, Southwire Corporation, 2nd Edition
  9. Manufacturer’s Instructions – Engineering Data for Copper and Aluminum Electrical Cables, The Okonite Company, Bulletin EHB-98.

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