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vault backup: 2026-04-23 17:46:59

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Zane Meyers
2026-04-23 17:46:59 -04:00
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nfpa-70_311_mv-conductors.md
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@@ -336,9 +336,7 @@ Cables shall be permitted to be marked to indicate special characteristics of th
Type MV cable shall be installed, terminated, and tested by qualified persons.
> [!info] 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.
> 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.
> [!info] 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.
@@ -373,9 +371,7 @@ Type MV cable shall be permitted for use on power systems rated up to and includ
Type MV conductors and cables used for direct burial applications shall be shielded, identified for such use, and installed in accordance with 300.50.
> [!important] 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.
The metallic shield, sheath, or armor shall be connected to a grounding electrode conductor, a grounding busbar, or a grounding electrode.
> Nonshielded multiconductor cables rated 2001 volts to 2400 volts shall be permitted if the cable has an overall metallic sheath or armor. The metallic shield, sheath, or armor shall be connected to a grounding electrode conductor, a grounding busbar, or a grounding electrode.
> [!important] 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.
@@ -428,13 +424,19 @@ Nonshielded, ozone-resistant insulated conductors with a maximum phase-to-phase
##### 311.60(A)(1) Tables or Engineering Supervision.
Ampacities for solid dielectric-insulated conductors shall be permitted to be determined by tables or under engineering supervision, as provided in 311.60(B) and (C).
Ampacities for solid dielectric-insulated conductors
shall be permitted to be determined by tables
or under engineering supervision,
as provided in 311.60(B) and (C).
The ampacity of Type MV cable installed in cable tray shall be determined in accordance with 392.80(B).
The ampacity of Type MV cable installed in cable tray
shall be determined in accordance with
[[nfpa-70_392_cable-tray#392.80(B) Ampacity of Type MV and Type MC Cables (2001 Volts or Over) in Cable Trays.|392.80(B)]].
##### 311.60(A)(2) Selection of Ampacity.
Where more than one calculated or tabulated ampacity could apply for a given circuit length, the lowest value shall be used.
Where more than one calculated or tabulated ampacity could apply for a given circuit length,
the lowest value shall be used.
> [!important] Exception:
> Where different ampacities apply to portions of a circuit, the higher ampacity shall be permitted to be used if the total portion(s) of the circuit with the lower ampacity does not exceed the lesser of 3.0 m (10 ft) or 10 percent of the total circuit.
@@ -446,7 +448,7 @@ Where more than one calculated or tabulated ampacity could apply for a given cir
Under engineering supervision, conductor ampacities shall be permitted to be calculated by using the following general equation:
### Equation 311.60(B)
##### Equation 311.60(B)
%% TODO %%
@@ -477,7 +479,8 @@ Ampacities for ambient temperatures other than those specified in the ampacity t
> For ampacities calculated in accordance with 311.60(A), reference IEEE 835, Standard Power Cable Ampacity Tables, and the references therein for availability of all factors and constants.
> [!info] Informational Note No. 2:
> Ampacities provided by this section do not take voltage drop into consideration. See 210.19(A), Informational Note No. 4, for branch circuits and 215.2(A), Informational Note No. 2, for feeders.
> Ampacities provided by this section do not take voltage drop into consideration.
> See 210.19(A), Informational Note No. 4, for branch circuits and 215.2(A), Informational Note No. 2, for feeders.
##### Table 311.60(C)(67) Ampacities of Insulated Single Copper Conductor Cables Triplexed in Air