---
id:
aliases:
  - nec-310
tags:
  - authorship/other
  - destiny/uncertain
  - status/incomplete
  - topic/construction/electrical
  - type/media
  - exclude-from-word-count
title: Article 310 Conductors for General Wiring
---
# Article 310: Conductors for General Wiring

## Part I. General

#### 310.1 Scope.

This article covers general requirements for conductors
rated up to and including 2000 volts
and their type designations, insulations, markings,
mechanical strengths, ampacity ratings, and uses.
These requirements do not apply to conductors that form an integral part of equipment,
such as motors, motor controllers, and similar equipment,
or to conductors specifically provided for elsewhere in this Code.

Informational Note:
For flexible cords and cables, see Article 400.
For fixture wires, see Article 402.

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## Part II. Construction Specifications

### 310.4 Conductor Constructions and Applications.

Insulated conductors shall comply with [[#Table 310.4(A) Conductor Applications and Insulations Rated 600 Volts|Table 310.4(A)]]
and [[#Table 310.4(B) Thickness of Insulation for Nonshielded Types RHH and RHW Solid Dielectric Insulated Conductors Rated 2000 Volts|Table 310.4(B)]].

Informational Note:
Thermoplastic insulation may stiffen at temperatures lower than −10°C (+14°F).
Thermoplastic insulation may also be deformed at normal temperatures
where subjected to pressure, such as at points of support.

### Table 310.4(A) Conductor Applications and Insulations Rated 600 Volts

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### Table 310.4(B) Thickness of Insulation for Nonshielded Types RHH and RHW Solid Dielectric Insulated Conductors Rated 2000 Volts

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## Part III. Installation

### 310.10 Uses Permitted.

The conductors described in [[#310.4 Conductor Constructions and Applications.|310.4]]
shall be permitted for use in any of the wiring methods covered in Chapter 3
and as specified in their respective tables
or as permitted elsewhere in this Code.

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### 310.14 Ampacities for Conductors Rated 0 Volts – 2000 Volts.

#### 310.14(A) General.

##### 310.14(A)(1) Tables or Engineering Supervision.

Ampacities for conductors shall be permitted to be determined by tables as provided in 310.15 or under engineering supervision, as provided in 310.14(B).

Informational Note No. 1:
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.

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### 310.15 Ampacity Tables.

#### 310.15(A) General.

Ampacities for conductors rated 0 volts to 2000 volts
shall be as specified in the Ampacity Table 310.16 through Table 310.21,
as modified by 310.15(A) through (F) and 310.12.
Under engineering supervision,
ampacities of sizes not shown in ampacity tables
for conductors meeting the general wiring requirements
shall be permitted to be determined by interpolation of the adjacent conductors
based on the conductor's area.
The temperature correction and adjustment factors
shall be permitted to be applied to the ampacity
for the temperature rating of the conductor,
if the corrected and adjusted ampacity does not exceed the ampacity
for the temperature rating of the termination
in accordance with the provisions of 110.14(C).

Informational Note No. 1:
Table 310.16 through Table 310.19 are application tables
for use in determining conductor sizes on loads
calculated in accordance with Part II, Part III, Part IV, or Part V of Article 220.
Ampacities result from consideration of one or more of the following:

* (1) Temperature compatibility with connected equipment, especially the connection points.
* (2) Coordination with circuit and system overcurrent protection.
* (3) Compliance with the requirements of product listings or certifications. See 110.3(B).
* (4) Preservation of the safety benefits of established industry practices and standardized procedures.

Informational Note No. 2:
For conductor area see Chapter 9, Table 8, Conductor Properties.
Interpolation is based on the conductor area
and not the conductor overall area.

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Informational Note No. 3:
For the ampacities of flexible cords and cables, see 400.5.
For the ampacities of fixture wires, see 402.5.

Informational Note No. 4:
For explanation of type letters used in tables
and for recognized sizes of conductors for the various conductor insulations,
see Table 310.4(A) and Table 310.4(B).
For installation requirements,
see 310.1 through 310.14 and the various articles of this Code.
For flexible cords,
see Table 400.4, Table 400.5(A)(1), and Table 400.5(A)(2).

#### 310.15(B) Ambient Temperature Correction Factors.

##### 310.15(B)(1) General.

Ampacities for ambient temperatures
other than those shown in the ampacity tables
shall be corrected in accordance with Table 310.15(B)(1) or Table 310.15(B)(2),
or shall be permitted to be calculated using Equation 310.15(B).

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$$
I\prime = I \sqrt{\frac{ T_c -T_{a}\prime }{ T_c - T_a }}
$$

where:

* $I\prime$ = ampacity corrected for ambient temperature
* $I$ = ampacity shown in the tables
* $T_c$ = temperature rating of conductor (°C)
* $T_{a}\prime$ = new ambient temperature (°C)
* $T_a$ = ambient temperature used in the table (°C)

##### 310.15(B)(2) Rooftop.

For raceways or cables exposed to direct sunlight on or above rooftops
where the distance above the roof
to the bottom of the raceway or cable is less than 23 mm (7⁄8 in.),
a temperature adder of 33°C (60°F) shall be added to the outdoor temperature
to determine the applicable ambient temperature
for application of the correction factors in Table 310.15(B)(1) or Table 310.15(B)(2).

Exception:
Type XHHW-2 insulated conductors shall not be subject to this ampacity adjustment.

Informational Note:
One source for the ambient temperatures in various locations
is the ASHRAE Handbook -- Fundamentals.

##### Table 310.15(B)(1) Ambient Temperature Correction Factors Based on 30°C (86°F)

For ambient temperatures other than 30°C (86°F),
multiply the ampacities specified in the ampacity tables
by the appropriate correction factor shown below.

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##### Table 310.15(B)(2) Ambient Temperature Correction Factors Based on 40°C (104°F)

For ambient temperatures other than 40°C (104°F),
multiply the ampacities specified in the ampacity tables
by the appropriate correction factor shown below.

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#### 310.15(C) Adjustment Factors.

##### 310.15(C)(1) More than Three Current-Carrying Conductors.

The ampacity of each conductor shall be reduced as shown in Table 310.15(C)(1)
where the number of current-carrying conductors in a raceway or cable exceeds three,
or where single conductors or multiconductor cables not installed in raceways
are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.).
Each current-carrying conductor of a paralleled set of conductors
shall be counted as a current-carrying conductor.

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##### Table 310.15(C)(1) Adjustment Factors for More Than Three Current-Carrying Conductors

| Number of Conductors* | Percent of Values in Table 310.16 Through Table 310.19 as Adjusted for Ambient Temperature if Necessary |
| --------------------- | ------------------------------------------------------------------------------------------------------- |
| 4–6                   | 80                                                                                                      |
| 7–9                   | 70                                                                                                      |
| 10–20                 | 50                                                                                                      |
| 21–30                 | 45                                                                                                      |
| 31–40                 | 40                                                                                                      |
| 41 and above          | 35                                                                                                      |

\*Number of conductors is the total number of conductors in the raceway or cable,
including spare conductors.
The count shall be adjusted in accordance with 310.15(E) and (F).
The count shall not include conductors
that are connected to electrical components
that cannot be simultaneously energized.

##### 310.15(C)(2) Raceway Spacing.

Spacing between raceways shall be maintained.

#### 310.15(D) Bare or Covered Conductors.

Where bare or covered conductors are installed with insulated conductors,
the temperature rating of the bare or covered conductor
shall be equal to the lowest temperature rating of the insulated conductors
for the purpose of determining ampacity.

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