Article 311 Medium Voltage Conductors and Cable
Medium Voltage Cable, Type MV. A single or multiconductor solid dielectric insulated cable rated 2001 volts up to and including 35,000 volts, nominal.
Thermal Resistivity. As used in this Code, the heat transfer capability through a substance by conduction.
Informational Note: Thermal resistivity is the reciprocal of thermal conductivity and is designated Rho, which is expressed in the units °C-cm/W.
Table 311.10(A) Conductor Application and Insulation Rated 2001 Volts and Higher
|Trade Name||Type Letter||Maximum
|Application Provision||Insulation||Outer Covering|
|Medium voltage solid dielectric||MV-90||90°C||Dry or wet locations||Thermoplastic or
|Jacket, sheath, or armor|
|*Where design conditions require maximum conductor temperatures above 90°C.|
|Conductor Size (AWG or kcmil)||Dry Locations, Single Conductor||Wet or Dry Locations|
|Without Jacket Insulation||With Jacket||Single Conductor||Multiconductor Insulation*|
|*Under a common overall covering such as a jacket, sheath, or armor.|
|Conductor Size (AWG or kcmil)||2001—5000 Volts||5001—8000 Volts||8001—15,000 Volts||15,001—25,000 Volts|
|100 Percent Insulation Level||100 Percent Insulation Level||133 Percent Insulation Level||173 Percent Insulation Level||100 Percent Insulation Level||133 Percent Insulation Level||173 Percent Insulation Level||100 Percent Insulation Level||133 Percent Insulation Level||173
Percent Insulation Level
|Conductor Size (AWG or kcmil)||25,001—28,000 Volts||28,001—35,000 Volts|
|100 Percent Insulation Level||133 Percent Insulation Level||173 Percent Insulation Level||100 Percent Insulation Level||133 Percent Insulation Level||173 Percent Insulation Level|
- In industrial establishments where the conditions of maintenance and supervision ensure only qualified persons service the installation
- Where the fault clearing time requirements of the 133 percent level category cannot be met
- Where an orderly shutdown is required to protect equipment and personnel
- Where the faulted section will be de-energized in an orderly shutdown
Cables shall be permitted to be used in 100 percent or 133 percent insulation level applications where the installation requires additional insulation.
Table 311.12(A) Minimum Size of Conductors
|Conductor Voltage Rating (Volts)||Minimum Conductor Size (AWG)|
|Copper, Aluminum, or Copper-Clad Aluminum|
- The maximum rated voltage
- The proper type letter or letters for the type of wire or cable as specified elsewhere in this Code
- The manufacturer's name, trademark, or other distinctive marking by which the organization responsible for the product can be readily identified
- The AWG size or circular mil area
Informational Note No. 1: Information about accepted industry practices and installation procedures for medium-voltage cable are described in ANSI/NECA/NCSCB 600, Standard for Installing and Maintaining Medium-Voltage Cable, and in IEEE 576, Recommended Practice for Installation, Termination, and Testing of Insulated Power Cables as Used in Industrial and Commercial Applications.
Informational Note No. 2: Where medium-voltage cable is used for dc circuits, low frequency polarization can create hazardous voltages. When handling the cable these voltages may be present or may develop on dc stressed cable while the circuit is energized. Solidly grounding the cable prior to contacting, cutting or disconnecting cables in dc circuits is a method to discharge these voltages.
- In wet or dry locations.
- In raceways.
- In cable trays, where identified for the use, in accordance with 392.10, 392.20(B), (C), and (D), 392.22(C), 392.30(B)(1), 392.46, 392.56, and 392.60. Type MV cable that has an overall metallic sheath or armor, complies with the requirements for Type MC cable, and is identified as "MV or MC" shall be permitted to be installed in cable trays in accordance with 392.10(B)(2).
- In messenger-supported wiring in accordance with Part II of Article 396.
- As exposed runs in accordance with 300.37. Type MV cable that has an overall metallic sheath or armor, complies with the requirements for Type MC cable, and is identified as "MV or MC" shall be permitted to be installed as exposed runs of metal-clad cable in accordance with 300.37.
- Corrosive conditions where 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.
- Conductors in parallel in accordance with 310.10(G).
- Type MV cable used where exposed to direct sunlight shall be identified for the use.
Informational Note: The "uses permitted" is not an all-inclusive list.
Exception No. 1: Nonshielded multiconductor cables rated 2001 volts to 2400 volts shall be permitted if the cable has an overall metallic sheath or armor.
Exception No. 2: Airfield lighting cable used in series circuits that are rated up to 5000 volts and are powered by regulators shall be permitted to be nonshielded.
Informational Note to Exception No. 2: Federal Aviation Administration (FAA) Advisory Circulars (ACs) provide additional practices and methods for airport lighting.