# PEC:Philippine Electrical Code 2009 Part 1/Chapter 3. Wiring Methods and Materials/Article 3.10 - Conductors For General Wiring

## Article 3.10 - Conductors For General Wiring

DISCLAIMER
This is not an official copy of the Philippine Electrical Code. This is a Design Guide according to the provisions of the Philippine Electrical Code. It also provides interpretation and annotations of the clauses of the Philippine Electrical Code. Any information, interpretation and/or annotation presented herein are based on personal opinion of the authors and does not represent the official interpretation of the Philippine Electrical Code.

While the authors have used good faith and efforts to ensure that the information and instructions contained in this work are accurate, the authors disclaim all responsibility for errors or omissions, including without limitation responsibility for damages resulting from the use of or reliance on this work. Use of the information and instructions contained in this work is at your own risk. If any contents or other technology this work contains or describes is subject to open source licenses or the intellectual property rights of others, it is your responsibility to ensure that your use thereof complies with such licenses and/or rights

Note: This is a work in progress...


### 3.10.1 General.

#### 3.10.1.1 Scope.

This article covers general requirements for conductors 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.

FPN: For flexible cords and cables, see Article 400. For fixture wires, see Article 4.2.

#### 3.10.1.2 Conductors.

##### (a) Insulated.

Conductors shall be insulated.

Exception: Where covered or bare conductors are specifically permitted elsewhere in this Code.

FPN: See 2.50.10.5 for insulation of neutral conductors of a solidly grounded high- voltage system.

##### (b) Conductor Material.

Conductors in this article shall be of aluminum, copper-clad aluminum, or copper unless otherwise specified.

#### 3.10.1.3 Stranded Conductors.

Where installed in raceways, conductors of size 8.0 mm 2 (3.2 mm dia.) and larger shall be stranded.

Exception: As permitted or required elsewhere in this Code.

#### 3.10.1.4 Conductors in Parallel.

Aluminum, copper-clad aluminum, or copper conductors of size 50 mm 2 and larger, comprising each phase, polarity, neutral, or grounded circuit conductor, shall be permitted to be connected in parallel (electrically joined at both ends).

Exception No. 1: As permitted in 6.20.2.2(a)(1).

Exception No. 2: Conductors in sizes smaller than 50 mm 2 shall be permitted to be run in parallel to supply control power to indicating instruments, contactors, relays, solenoids, and similar control devices, provided all of the following apply:

(a) They are contained within the same raceway or cable.
(b) The ampacity of each individual conductor is sufficient to carry the entire load current shared by the parallel conductors.
(c) The overcurrent protection is such that the ampacity of each individual conductor will not be exceeded if one or more of the parallel conductors become inadvertently disconnected.

Exception No. 3: Conductors in sizes smaller than 50 mm 2 shall be permitted to be run in parallel for frequencies of 360 Hz and higher where conditions (a), (b), and (c) of Exception No. 2 are met.

Exception No. 4: Under the supervision of a licensed electrical engineer, grounded neutral conductors in sizes 30 mm 2 and larger shall be permitted to be run in parallel for existing installations.

FPN: Exception No. 4 can be used to alleviate overheating of neutral conductors in existing installations due to high content of triplen harmonic currents.

The paralleled conductors in each phase, polarity, neutral, or grounded circuit conductor shall comply with all of the following:

(1) Be the same length
(2) Have the same conductor material
(3) Be the same cross sectional area of the conducting material
(4) Have the same insulation type
(5) Be terminated in the same manner

Where run in separate raceways or cables, the raceways or cables shall have the same physical characteristics. Where conductors are in separate raceways or cables, the same number of conductors shall be used in each raceway or cable. Conductors of one phase, polarity, neutral, or grounded circuit conductor shall not be required to have the same physical characteristics as those of another phase, polarity, neutral, or grounded circuit conductor to achieve balance.

FPN: Differences in inductive reactance and unequal division of current can be minimized by choice of materials, methods of construction, and orientation of conductors.

Where equipment grounding conductors are used with conductors in parallel, they shall comply with the requirements of this section except that they shall be sized in accordance with 2.50.6.13.

Conductors installed in parallel shall comply with the provisions of 3.10.1.15(b)(2)(a).

#### 3.10.1.5 Minimum Size of Conductors.

The minimum size of conductors shall be as shown in Table 3.10.1.5, except as permitted elsewhere in this Code.

Table 3.10.1.5 Minimum Size of Conductors
Conductor Voltage Rating (Volts) Minimum Conductor Size mm2 (mm dia.)
Copper Aluminum or Copper-Clad Aluminum
0–2000 2.0(1.6) 3.5(2.0)
2001–8000 8.0(3.2) 8.0(3.2)
8001–15,000 30 30
15,001–28,000 38 38
28,001–35,000 50 50

#### 3.10.1.6 Shielding.

Solid dielectric insulated conductors operated above 2000 volts in permanent installations shall have ozone-resistant insulation and shall be shielded. All metallic insulation shields shall be grounded through an effective grounding path meeting the requirements of 2.50.1.4(a)(5) or 2.50.1.4(b)(4). Shielding shall be for the purpose of confining the voltage stresses to the insulation. Exception: Nonshielded insulated conductors listed by a qualified testing laboratory shall be permitted for use up to 2 400 volts under the following conditions:

(a) Conductors shall have insulation resistant to electric discharge and surface tracking, or the insulated conductor(s) shall be covered with a material resistant to ozone, electric discharge, and surface tracking.

(b) Where used in wet locations, the insulated conductor(s) shall have an overall nonmetallic jacket or a continuous metallic sheath.

(c) Insulation and jacket thicknesses shall be in accordance with Table 3.10.1.63.

#### 3.10.1.7 Direct Burial Conductors.

Conductors used for direct burial applications shall be of a type identified for such use. Cables rated above 2 000 volts shall be shielded. Exception: Nonshielded multiconductor cables rated 2 001– 5000 volts shall be permitted if the cable has an overall metallic sheath or armor.

The metallic shield, sheath, or armor shall be grounded through an effective grounding path meeting the requirements of 2.50.1.4(a)(5) or (b)(4).

FPN No. 1: See 3.0.1.5 for installation requirements for conductors rated 600 volts or less.

FPN No. 2: See 3.0.2.20 for installation requirements for conductors rated over 600 volts.

#### 3.10.1.8 Locations.

##### (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 or cables used where exposed to direct rays of the sun shall comply with one of the following:

(1) Cables listed, or listed and marked, as being sunlight resistant
(2) Conductors listed, or listed and marked, as being sunlight resistant
(3) Covered with insulating material, such as tape or sleeving, that is listed, or listed and marked, as being sunlight resistant

#### 3.10.1.9 Corrosive Conditions.

onductors 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.

==== 3.10.1.10 Temperature Limitation of Conductors. No conductor shall be used in such a manner that its operating temperature exceeds that designated for the type of insulated conductor involved. In no case shall conductors be associated together in such a way, with respect to type of circuit, the wiring method employed, or the number of conductors, that the limiting temperature of any conductor is exceeded.

FPN No. 1: The temperature rating of a conductor (see Table 3.10.1.13 and Table 3.10.1.61) is the maximum temperature, at any location along its length, that the conductor can withstand over a prolonged time period without serious degradation.

The allowable ampacity tables, the ampacity tables of Article 3.10 and the ampacity tables of Annex B, the correction factors at the bottom of these tables, and the notes to the tables provide guidance for coordinating conductor sizes, types, allowable ampacities, ampacities, ambient temperatures, and number of associated conductors.

The principal determinants of operating temperature are as follows:

(1) Ambient temperature — ambient temperature may vary along the conductor length as well as from time to time.

(2) Heat generated internally in the conductor as the result of load current flow, including fundamental and harmonic currents.

(3) The rate at which generated heat dissipates into the ambient medium. Thermal insulation that covers or surrounds conductors affects the rate of heat dissipation.

(4) Adjacent load-carrying conductors — adjacent conductors have the dual effect of raising the ambient temperature and impeding heat dissipation. FPN No. 2: Conductors installed in conduit exposed to direct sunlight in close proximity to rooftops have been shown, under certain conditions, to experience a temperature rise of 17°C (30°F) above ambient temperature on which the ampacity is based.

#### 3.10.1.11 Marking.

##### (a) Required Information.

All conductors and cables shall be marked to indicate the following information, using the applicable method described in 3.10.1.11(b):

(1) The maximum rated voltage

(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 size in millimeter square or millimeter diameter

FPN: See Conductor Properties, Table 8 of Chapter 9, for conductor area expressed in SI units for conductor sizes specified in mm 2 or mm dia.

(5) Cable assemblies where the neutral conductor is smaller than the ungrounded conductors shall be so marked

##### (b) Method of Marking.
###### (1) Surface Marking.

The following conductors and cables shall be durably marked on the surface. The size in mm 2 or mm diameter shall be repeated at intervals not exceeding 600 mm. All other markings shall be repeated at intervals not exceeding 1 000 mm.

a. Single-conductor 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 3.10.1.11(a) shall be permitted to be durably marked on the outer nonmetallic covering of Type MC, Type ITC, or Type PLTC cables at intervals not exceeding 1.0 m (40 in.).

Exception No. 4: The information required in 3.10.1.11(a) shall be permitted to be durably marked on a nonmetallic covering under the exceeding 1 000 mm. metallic sheath of Type ITC or Type PLTC cable at intervals not

FPN: Included in the group of metal-covered cables are Type AC cable (Article 3.20), Type MC cable (Article 3.30), and lead-sheathed cable.

###### (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. Type AC cable

###### (4) Optional Marking of Wire Size.

The information required in 3.10.1.11(a)(4) 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 letter suffixes shall be indicated as follows:

(1) D — For two insulated conductors laid parallel within an outer nonmetallic covering

(2) 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. These markings include, but are not limited to, markings for limited smoke, sunlight resistant, and so forth.

#### 3.10.1.12 Conductor Identification.

##### (a) Grounded Conductors.

Insulated or covered grounded conductors shall be identified in accordance with 2.0.1.6.

##### (b) Equipment Grounding Conductors.

Equipment grounding conductors shall be in accordance with 2.50.6.10.

##### (c) Ungrounded Conductors.

Conductors that are intended for use as ungrounded conductors, whether used as a single conductor or in multiconductor cables, shall be finished to be clearly distinguishable from grounded and grounding conductors. Distinguishing markings shall not conflict in any manner with the surface markings required by 3.10.1.11(b)(1). Branch-circuit ungrounded conductors shall be identified in accordance with 2.10.1.5(c). Feeders shall be identified in accordance with 2.15.1.12.

Exception: Conductor identification shall be permitted in accordance with 2.0.1.7.

#### 3.10.1.13 Conductor Constructions and Applications.

Insulated conductors shall comply with the applicable provisions of one or more of the following: Table 3.10.1.13, Table 3.10.1.61, Table 3.10.1.62, Table 3.10.1.63, and Table 3.10.1.64.

These conductors shall be permitted for use in any of the wiring methods recognized in Chapter 3 and as specified in their respective tables or as permitted elsewhere in this Code.

FPN: Thermoplastic insulation may stiffen at t emperatures 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. Thermoplastic insulation, where used on dc circuits in wet locations, may result in electroendosmosis between conductor and insulation.

#### 3.10.1.14 Aluminum Conductor Material.

Solid aluminum conductors 8.0(3.2), 5.5(2.6), and 3.5(2.0) mm 2 (dia.) shall be made of an AA-8000 series electrical grade aluminum alloy conductor material. Stranded aluminum conductors 8.0 mm 2 (3.2 mm dia.) through 500 mm 2 marked as Type RHH, RHW, XHHW, THW, THHW, THWN, THHN, service-entrance Type SE Style U and SE Style R shall be made of an AA-8000 series electrical grade aluminum alloy conductor material.

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

##### (a) General.
###### (1) Tables or Engineering Supervision.

Ampacities for conductors shall be permitted to be determined by tables as provided in 3.10.1.15(b) or under engineering supervision, as provided in 3.10.1.15(c).

FPN No. 1: Ampacities provided by this section do not take voltage drop into consideration. See 2.10.2.1(a), FPN No. 4, for branch circuits and 2.15.1.2(a), FPN No. 2, for feeders.

FPN No. 2: For the allowable ampacities of Type MTW wire, see Table 13.5.1 in NFPA 79-2002, Electrical Standard for Industrial Machinery.

###### (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.

Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3 000 mm or 10 percent of the circuit length figured at the higher ampacity, whichever is less.

FPN: See 1.10.1.14(c) for conductor temperature limitations due to termination provisions.

##### (b) Tables.

Ampacities for conductors rated 0 to 2000 volts shall be as specified in the Allowable Ampacity Table 3.10.1.16 through Table 3.10.1.19, and Ampacity Table 3.10.1.20 and Table 3.10.1.21 as modified by (b)(1) through (b)(6).

FPN: Table 3.10.1.16 through Table 3.10.1.19 are application tables for use in determining conductor sizes on loads calculated in accordance with Article 220.

Allowable 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.
###### (1) General.

For explanation of type letters used in tables and for recognized sizes of conductors for the various conductor insulations, see 3.10.1.13. For installation requirements, see 3.10.1.1 through 3.10.1.10 and the various articles of this Code. For flexible cords, see Table 4.0.1.4, Table 4.0.1.5(a), and Table 4.0.1.5(b).

###### (2) Adjustment Factors.

a. More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are stacked or bundled longer than 600 mm without maintaining spacing and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 3.10.1.15(b)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

FPN No. 1: See Annex B, Table B.3.10.1.11, for adjustment factors for more than three current-carrying conductors in a raceway or cable with load diversity. FPN No. 2: See 3.66.2.14(a) for correction factors for conductors in sheet metal auxiliary gutters and 3.76.2.13 for correction factors for conductors in metal wireways.

Exception No. 1: Where conductors of different systems, as provided in 3.0.1.3, are installed in a common raceway or cable, the derating factors shown in Table 3.10.1.15(b)(2)(a) shall apply only to the number of power and lighting conductors (Articles 2.10, 2.15, 2.20, and 2.30).

Exception No. 2: For conductors installed in cable trays, the provisions of 3.92.1.11 shall apply. Exception No. 3: Derating factors shall not apply to conductors in nipples having a length not exceeding 600 mm.

Exception No. 4: Derating factors shall not apply to underground conductors entering or leaving an outdoor trench if those conductors have physical protection in the form of rigid metal conduit, intermediate metal conduit, or rigid nonmetallic conduit having a length not exceeding 3 000 mm and if the number of conductors does not exceed four.

Exception No. 5: Adjustment factors shall not apply to Type AC cable or to Type MC cable without an overall outer jacket under the following conditions:

(1) Each cable has not more than three current-carrying conductors. (2) The conductors are 3.5 mm 2 (2.0 mm dia.) copper. (3) Not more than 20 current-carrying conductors are bundled, stacked, or supported on “bridle rings.”

A 60 percent adjustment factor shall be applied where the current- carrying conductors in these cables that are stacked or bundled longer than 600 mm without maintaining spacing exceeds 20.

Table 3.10.1.15(b)(2)(a) Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable
Number of Current-Carrying Conductors Percent of Values in Tables 3.10.1.16 through 3.10.1.19 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

b. More Than One Conduit, Tube, or Raceway. Spacing between conduits, tubing, or raceways shall be maintained.

###### (3) Bare or Covered Conductors.

Where bare or covered conductors are used with insulated conductors, their allowable ampacities shall be limited to those permitted for the adjacent insulated conductors.

###### (4) Neutral Conductor.

a. A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 3.10.1.15(b)(2)(a).

b. In a 3-wire circuit consisting of two phase wires and the neutral of a 4-wire, 3-phase, wye-connected system, a common conductor carries approximately the same current as the line-to-neutral load currents of the other conductors and shall be counted when applying the provisions of 3.10.1.15(b)(2)(a).

c. On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral shall therefore be considered a current-carrying conductor.

###### (5) Grounding or Bonding Conductor.

A grounding or bonding conductor shall not be counted when applying the provisions of 3.10.1.15(b)(2)(a).

###### (6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders.

For individual dwelling units of one family, two-family, and multifamily dwellings, conductors, as listed in Table 3.10.1.15(b)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service- entrance conductors, service lateral conductors, and feeder conductors that serve as the main power feeder to each dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circuit panelboards(s). The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 2.15.1.2, 2.20.3.22, and 2.30.4.3 are met.

Table 3.10.1.15(b)(6) Conductor Types and Sizes for 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. Conductor Types RHH, RHW, RHW-2, THHN, THHW, THW, THW-2, THWN, THWN-2, XHHW, XHHW-2, SE, USE, USE-2
Conductor mm2 Service or Feeder Rating (Amperes)
Copper Aluminum or Copper-Clad Aluminum
22 30 100
30 30 110
30 50 125
38 60 150
50 80 175
60 100 200
80 125 225
100 150 250
125 175 300
175 250 350
200 325 400
##### (c) Engineering Supervision.

Under engineering supervision, conductor ampacities shall be permitted to be calculated by means of the following general formula:

$I=\sqrt{\frac{TC – (TA + ΔTD)}{RDC(1 + YC)RCA}}$

where:

TC= conductor temperature in degrees Celsius (°C)
TA= ambient temperature in degrees Celsius (°C)
TD= dielectric loss temperature rise
RDC= dc resistance of conductor at temperature TC
YC= component ac resistance resulting from skin effect and proximity effect
RCA= effective thermal resistance between conductor and surrounding ambient

Table 3.10.1.16 Allowable Ampacities of Insulated Conductors Rated 0 Through 2000 Volts, 60°C Through 90°C (140°F Through 194°F), Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30°C (86°F)
Size mm2 (mm dia.) Temperature Rating of Conductor (See Table 3.10.1.13.) Size mm2 (mm dia.)
60°C (140°F) 75°C (167°F) 90°C (194°F) 60°C (140°F) 75°C (167°F) 90°C (194°F)
Types TW, UF Types RHW, THHW, THW, THWN, XHHW, USE, ZW Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE- 2, XHH, XHHW, XHHW-2, ZW- 2 Types TW, UF Types RHW, THHW, THW, THWN, XHHW, USE, ZW Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE- 2, XHH, XHHW, XHHW-2, ZW- 2
COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
2.0(1.6)* 20 20 25 2.0(1.6)*
3.5(2.0)* 25 25 30 20 20 25 3.5(2.0)*
5.5(2.6)* 30 35 40 25 30 35 5.5(2.6)*
8.0(3.2) 40 50 55 30 40 45 8.0(3.2)
14 55 65 70 40 50 60 14
22 70 85 90 55 65 80 22
30 90 110 115 65 80 90 30
38 100 125 130 75 90 105 38
50 120 145 150 95 110 125 50
60 135 160 170 100 120 135 60
80 160 195 205 120 145 165 80
100 185 220 225 140 170 190 100
125 210 255 265 165 200 225 125
150 240 280 295 185 225 250 150
175 260 305 345 205 245 275 175
200 280 330 355 220 265 300 200
250 315 375 400 255 305 345 250
325 370 435 470 305 365 410 325
375 395 470 530 315 380 430 375
400 405 485 515 335 405 460 400
500 445 540 580 370 440 495 500
CORRECTION FACTORS
Ambient Temp. (°C) For ambient temperatures other than 30°C (86°F), multiply the allowable ampacities shown above by the appropriate factor shown below. Ambient Temp. (°F)
21–25 1.08 1.05 1.04 1.08 1.05 1.04 70-77
26-30 1.00 1.00 1.00 1.00 1.00 1.00 78-86
31-35 0.91 0.94 0.96 0.91 0.94 0.96 87-95
36-40 0.82 0.88 0.91 0.82 0.88 0.91 96-104
41-45 0.71 0.82 0.87 0.71 0.82 0.87 105-113
46-50 0.58 0.75 0.82 0.58 0.75 0.82 114-122
51-55 0.41 0.67 0.76 0.41 0.67 0.76 123-131
56-60 0.58 0.71 0.58 0.71 132-140
61-70 0.33 0.58 0.33 0.58 141-158
71-80 0.41 0.41 159-176
* See 2.40.1.4(d).

Table 3.10.1.17 Allowable Ampacities of Single-Insulated Conductors Rated 0 Through 2000 Volts in Free Air, Based on Ambient Air Temperature of 30°C (86°F)
Size mm2 (mm dia.) Temperature Rating of Conductor (See Table 3.10.1.13.) Size mm2 (mm dia.)
60°C (140°F) 75°C (167°F) 90°C (194°F) 60°C (140°F) 75°C (167°F) 90°C (194°F)
Types TW, UF Types RHW, THHW, THW, THWN, XHHW, USE, ZW Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE- 2, XHH, XHHW, XHHW-2, ZW- 2 Types TW, UF Types RHW, THHW, THW, THWN, XHHW, USE, ZW Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE- 2, XHH, XHHW, XHHW-2, ZW- 2
COPPER ALUMINUM OR COPPER-CLAD ALUMINUM
2.0(1.6)* 25 30 35 2.0(1.6)*
3.5(2.0)* 30 35 40 25 30 35 3.5(2.0)*
5.5(2.6)* 40 50 55 35 40 40 5.5(2.6)*
8.0(3.2) 55 65 75 45 50 55 8.0(3.2)
14 80 95 105 65 80 85 14
22 105 130 140 85 105 115 22
30 130 160 170 95 115 130 30
38 155 185 195 115 135 155 38
50 180 220 235 135 165 185 50
60 205 250 260 155 185 210 60
80 250 300 320 185 225 255 80
100 290 355 370 220 265 295 100
125 335 400 420 260 310 350 125
150 375 440 475 295 355 400 150
175 410 495 560 325 390 440 175
200 440 540 570 345 410 465 200
250 505 620 655 405 485 545 250
325 600 720 770 475 560 640 325
375 645 775 875 510 615 690 375
400 675 810 875 530 640 725 400
500 770 930 995 620 745 835 500
CORRECTION FACTORS
Ambient Temp. (°C) For ambient temperatures other than 30°C (86°F), multiply the allowable ampacities shown above by the appropriate factor shown below. Ambient Temp. (°F)
21–25 1.08 1.05 1.04 1.08 1.05 1.04 70-77
26-30 1.00 1.00 1.00 1.00 1.00 1.00 78-86
31-35 0.91 0.94 0.96 0.91 0.94 0.96 87-95
36-40 0.82 0.88 0.91 0.82 0.88 0.91 96-104
41-45 0.71 0.82 0.87 0.71 0.82 0.87 105-113
46-50 0.58 0.75 0.82 0.58 0.75 0.82 114-122
51-55 0.41 0.67 0.76 0.41 0.67 0.76 123-131
56-60 0.58 0.71 0.58 0.71 132-140
61-70 0.33 0.58 0.33 0.58 141-158
71-80 0.41 0.41 159-176
* See 2.40.1.4(d).

Table 3.10.1.18 Allowable Ampacities of Insulated Conductors Rated 0 Through 2000 Volts, 150°C Through 250°C (302°F Through 482°F). Not More Than Three Current-Carrying Conductors in Raceway or Cable, Based on Ambient Air Temperature of 40°C (104°F)
Size mm2 (mm dia.) Temperature Rating of Conductor (See Table 3.10.1.13.) Size mm2 (mm dia.)
150°C (302°F) 200°C (392°F) 250°C (482°F) 150°C (302°F)
Type Z Types FEP, FEPB, PFA, SA Types PFAH, TFE Type Z
COPPER NICKEL OR NICKEL-COATED COPPER ALUMINUM OR COPPER- CLAD ALUMINUM
2.0(1.6) 34 36 39 2.0(1.6)
3.5(2.0) 43 45 54 30 3.5(2.0)
5.5(2.6) 55 60 73 44 5.5(2.6)
8.0(3.2) 76 83 93 57 8.0(3.2)
14 96 110 117 75 14
22 120 125 148 94 22
30 143 152 166 109 30
30 160 171 191 124 30
38 186 197 215 145 38
50 215 229 244 169 50
60 251 260 273 198 60
80 288 297 308 227 80
100 332 346 361 260 100
CORRECTION FACTORS
Ambient Temp. (°C) For ambient temperatures other than 40°C (104°F), multiply the allowable ampacities shown above by the appropriate factor shown below. Ambient Temp. (°F)
41-50 0.95 0.97 0.98 0.95 105-122
51-60 0.90 0.94 0.95 0.90 123-140
61-70 0.85 0.90 0.93 0.85 141-158
71-80 0.80 0.87 0.90 0.80 159-176
81-90 0.74 0.83 0.87 0.74 177-194
91-100 0.67 0.79 0.85 0.67 195-212
101-120 0.52 0.71 0.79 0.52 213-248
121-140 0.30 0.61 0.72 0.30 249-284
141-160 0.50 0.65 285-320
161-180 0.35 0.58 321-356
181-200 0.49 357-392
201-225 0.35 393-437

Table 3.10.1.19 Allowable Ampacities of Single-Insulated Conductors, Rated 0 Through 2 000 Volts, 150°C Through 250°C (302°F Through 482°F), in Free Air, Based on Ambient Air Temperature of 40°C (104°F)
Size mm2 (mm dia.) Temperature Rating of Conductor (See Table 3.10.1.13.) Size mm2 (mm dia.)
150°C (302°F) 200°C (392°F) 250°C (482°F) 150°C (302°F)
Type Z Types FEP, FEPB, PFA, SA Types PFAH, TFE Type Z
COPPER NICKEL OR NICKEL-COATED COPPER ALUMINUM OR COPPER- CLAD ALUMINUM
2.0(1.6) 46 54 59 2.0(1.6)
3.5(2.0) 60 68 78 47 3.5(2.0)
5.5(2.6) 80 90 107 63 5.5(2.6)
8.0(3.2) 106 124 142 83 8.0(3.2)
14 155 165 205 112 14
22 190 220 278 148 22
30 214 252 327 170 30
30 255 293 381 198 30
38 293 344 440 228 38
50 339 399 532 263 50
60 390 467 591 305 60
80 451 546 708 351 80
100 529 629 830 411 100
CORRECTION FACTORS
Ambient Temp. (°C) For ambient temperatures other than 40°C (104°F), multiply the allowable ampacities shown above by the appropriate factor shown below. Ambient Temp. (°F)
41-50 0.95 0.97 0.98 0.95 105-122
51-60 0.90 0.94 0.95 0.90 123-140
61-70 0.85 0.90 0.93 0.85 141-158
71-80 0.80 0.87 0.90 0.80 159-176
81-90 0.74 0.83 0.87 0.74 177-194
91-100 0.67 0.79 0.85 0.67 195-212
101-120 0.52 0.71 0.79 0.52 213-248
121-140 0.30 0.61 0.72 0.30 249-284
141-160 0.50 0.65 285-320
161-180 0.35 0.58 321-356
181-200 0.49 357-392
201-225 0.35 393-437

Table 3.10.1.20 Ampacities of Not More Than Three Single Insulated Conductors, Rated 0 Through 2 000 Volts, Supported on a Messenger, Based on Ambient Air Temperature of 40°C (104°F)
Size mm2 (mm dia.) Temperature Rating of Conductor (See Table 3.10.1.13.) Size mm2 (mm dia.)
150°C (302°F) 200°C (392°F) 250°C (482°F) 150°C (302°F)
Type Z Types FEP, FEPB, PFA, SA Types PFAH, TFE Type Z
COPPER NICKEL OR NICKEL-COATED COPPER ALUMINUM OR COPPER- CLAD ALUMINUM
8.0(3.2) 53 62 41 48 8.0(3.2)
14 80 94 62 73 14
22 105 121 81 94 22
30 116 136 91 106 30
38 138 162 107 126 38
50 165 193 129 150 50
60 187 218 146 170 60
80 227 266 178 208 80
100 270 315 210 246 100
125 316 369 248 288 125
150 363 423 285 331 150
175 175
200 416 486 327 382 200
250 496 581 392 458 250
325 576 674 458 535 325
375 375
400 659 771 529 617 400
500 741 870 606 709 500
CORRECTION FACTORS
Ambient Temp. (°C) For ambient temperatures other than 40°C (104°F), multiply the allowable ampacities shown above by the appropriate factor shown below. Ambient Temp. (°F)
21-25 1.20 1.14 1.20 1.14 70-77
26-30 1.13 1.10 1.13 1.10 19-86
31-35 1.07 1.05 1.07 1.05 88-95
36-40 1.00 1.00 1.00 1.00 97-104
41-45 0.93 0.95 0.93 0.95 106-113
46-50 0.85 0.89 0.85 0.89 115-122
51-55 0.76 0.84 0.76 0.84 124-131
56-60 0.65 0.77 0.65 0.77 133-140
61-70 0.38 0.63 0.38 0.63 142-158
71-80 0.45 0.45 160-176

Table 3.10.1.21 Ampacities of Bare or Covered Conductors in Free Air, Based on 40°C (104°F) Ambient, 80°C (176°F) Total Conductor Temperature, 610 mm/sec (2 ft/sec) Wind Velocity
Copper Conductors AAC Aluminum Conductors
Bare Covered Bare Covered
mm2 (mm dia.) Amperes mm2 (mm dia.) Amperes mm2 (mm dia.) Amperes mm2 (mm dia.) Amperes
8.0(3.2) 92 8.0(3.2) 97 8.0(3.2) 71 8.0(3.2) 75
14 131 14 137 14 101 14 106
22 161 22 169 22 125 22 132
30 180 30 189 30 141 30 147
50 254 50 268 50 198 50 208
60 291 60 304 60 225 60 237
80 354 80 372 80 275 80 289
100 417 100 438 100 325 100 342
125 98 125 18
125 488 125 512 150 473 150 497
150 562 150 590 175 175
175 175 200 505 200 530
250 774 250 813 250 651 250 683
375 375 325 738 325 775
400 1033 400 1084 375 375
500 1181 500 1241 400 846 400 888
500 911

#### 3.10.1.60 Conductors Rated 2001 to 35,000 Volts.

##### (a) Definitions.
###### Electrical Ducts.

As used in Article 3.10, electrical ducts shall include any of the electrical conduits recognized in Chapter 3 as suitable for use underground; other raceways round in cross section, listed for underground use, and embedded in earth or concrete.

###### Thermal Resistivity.

As used in this Code, the heat transfer capability through a substance by conduction. It is the reciprocal of thermal conductivity and is designated Rho and expressed in the units °C-cm/watt.

##### (b) Ampacities of Conductors Rated 2001 to 35,000 Volts.

Ampacities for solid dielectric-insulated conductors shall be permitted to be determined by tables or under engineering supervision, as provided in 3.10.1.60(c) and (d).

###### (1) Selection of Ampacity.

Where more than one calculated or tabulated ampacity could apply for a given circuit length, the lowest value shall be used.

Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3 000 mm or 10 percent of the circuit length figured at the higher ampacity, whichever is less.

FPN: See 1.10.3.11 for conductor temperature limitations due to termination provisions.

##### (c) Tables.

Ampacities for conductors rated 2001 to 35,000 volts shall be as specified in the Ampacity Table 3.10.1.67 through Table 3.10.1.86. Ampacities at ambient temperatures other than those shown in the tables shall be determined by the formula in 3.10.1.60(c)(4).

FPN No. 1: For ampacities calculated in accordance with 3.10.1.60(b), reference IEEE 835-1994 (IPCEA Pub. No. P-46-426), Standard Power Cable Ampacity Tables, and the references therein for availability of all factors and constants.

FPN No. 2: Ampacities provided by this section do not take voltage drop into consideration. See 2.10.2.1(a), FPN No. 4, for branch circuits and 2.15.1.2(a), FPN No. 2, for feeders.

###### (1) Grounded Shields.

Ampacities shown in Table 3.10.1.69, Table 3.10.1.70, Table 3.10.1.81, and Table 3.10.1.82 are for cable with shields grounded at one point only. Where shields are grounded at more than one point, ampacities shall be adjusted to take into consideration the heating due to shield currents.

###### (2) Burial Depth of Underground Circuits.

Where the burial depth of direct burial or electrical duct bank circuits is modified from the values shown in a figure or table, ampacities shall be permitted to be modified as indicated in (c)(1) and (c)(2).

a. Where burial depths are increased in part(s) of an electrical duct run, no decrease in ampacity of the conductors is needed, provided the total length of parts of the duct run increased in depth is less than 25 percent of the total run length.
b. Where burial depths are deeper than shown in a specific underground ampacity table or figure, an ampacity derating factor of 6 percent per 300 mm increase in depth for all values of rho shall be permitted.
No rating change is needed where the burial depth is decreased.
###### (3) Electrical Ducts in Figure 3.10.1.60.

At locations where electrical ducts enter equipment enclosures from under ground, spacing between such ducts, as shown in Figure 3.10.1.60, shall be permitted to be reduced without requiring the ampacity of conductors therein to be reduced.

###### (4) Ambients Not in Tables.

Ampacities at ambient temperatures other than those shown in the tables shall be determined by means of the following formula:

$I_2=I_1 \sqrt{\frac{TC – TA_2 + ΔTD}{TC – TA_1 + ΔTD}}$

where:

I1 = ampacity from tables at ambient TA1
I2 = ampacity at desired ambient TA2
TC= conductor temperature in degrees Celsius (°C)
TA1 = surrounding ambient from tables in degrees Celsius (°C)
TA2 = desired ambient in degrees Celsius (°C)
TD= dielectric loss temperature rise

##### (d) Engineering Supervision.

Under engineering supervision, conductor ampacities shall be permitted to be calculated by means of the following general formula:

$I=\sqrt{\frac{TC – (TA + ΔTD)}{RDC(1 + YC)RCA}}$

where:

TC= conductor temperature in degrees Celsius (°C)
TA= ambient temperature in degrees Celsius (°C)
TD= dielectric loss temperature rise
RDC= dc resistance of conductor at temperature TC
YC= component ac resistance resulting from skin effect and proximity effect
RCA= effective thermal resistance between conductor and surrounding ambient

FPN: See Appendix B for examples of formula applications.

Table 3.10.1.61 Conductor Application and Insulation
Trade Name Type Letter Maximum Operating Temperature Application Provision Insulation Outer Covering
Medium voltage solid dielectric MV-90
MV-105*
90°C
105°C
Dry or wet locations rated 2001 volts and higher Thermoplastic or thermosetting Jacket, sheath, or armor
* Where design conditions require maximum conductor temperatures above 90°C.

Table 3.10.1.62 Thickness of Insulation for 601- to 2000-Volt Nonshielded Types RHH and RHW
Conductor Size mm2 (mm dia.) Column A1 mm Column B2 mm
2.0(1.6)–5.5(2.6) 2.03 1.52
8.0(3.2) 2.03 1.78
14 – 30 2.41 1.78
38 – 60 2.79 2.29
80 – 100 2.79 2.29
213 – 250 3.18 2.67
251 – 500 3.56 3.05
501 – 1000 3.56 3.56
1 Column A insulations are limited to natural, SBR, and butyl rubbers.

2 Column B insulations are materials such as cross-linked polyethylene, ethylene propylene rubber, and composites thereof.

Table 3.10.1.63 Thickness of Insulated Conductors Rated 2400 Volts and Jacket for Nonshielded Solid Dielectric Insulation
Conductor Size mm2 (mm dia.) Dry Locations, Single Conductor Wet or Dry Locations
Without Jacket Insulation (mm) With Jacket Single Conductor Multiconductor Insulation* (mm)
Insulation (mm) Jacket (mm) Insulation (mm) Jacket (mm)
8.0(3.2) 2.79 2.29 0.76 3.18 2.03 2.29
14 2.79 2.29 0.76 3.18 2.03 2.29
22 – 30 2.79 2.29 1.14 3.18 2.03 2.29
38 – 60 2.79 2.29 1.14 3.18 2.03 2.29
80 – 100 2.79 2.29 1.65 3.18 2.41 2.29
213 – 250 3.05 2.29 1.65 3.56 2.79 2.29
251 – 400 3.3 2.29 1.65 3.94 3.18 2.29
401 – 500 3.3 2.29 1.65 3.94 3.18 2.29
* Under a common overall covering such as a jacket, sheath, or armor.

Table 3.10.1.64 Thickness of Insulation for Shielded Solid Dielectric Insulated Conductors Rated 2001 to 35,000 Volts
Conductor Size mm2 (mm dia.) 2001– 5000 Volts (mm) 5001–8000 volts 8001–15,000 volts 15,001–25,000 volts
100 Percent Insulation Level 1 133 Percent Insulation Level 2 173 Percent Insulation Level 3 100 Percent Insulation Level 1 133 Percent Insulation Level 2 173 Percent Insulation Level 3 100 Percent Insulation Level 1 133 Percent Insulation Level 2 173 Percent Insulation Level 3
8.0(3.2) 2.29
14 – 22 2.29 2.92 3.56 4.45
30 2.29 2.92 3.56 4.45 4.45 5.59 6.6
38 2.29 2.92 3.56 4.45 4.45 5.59 6.6 6.6 8.13 10.67
50 – 1000 2.29 2.92 3.56 4.45 4.45 5.59 6.6 6.6 8.13 10.67
Conductor Size mm2 (mm dia.) 2001– 5000 Volts (mm) 25 001–28 000 volts 28 001–35 000 volts -
100 Percent Insulation Level 1 133 Percent Insulation Level 2 173 Percent Insulation Level 3 100 Percent Insulation Level 1 133 Percent Insulation Level 2 173 Percent Insulation Level 3 - - -
38 2.29 7.11 8.76 11.3 - - -
50 – 1000 2.29 7.11 8.76 11.3 8.76 10.67 14.73 - - -
Notes:

1 100 Percent Insulation Level. Cables in this category shall be permitted to be applied where the system is provided with relay protection such that ground faults will be cleared as rapidly as possible but, in any case, within 1 minute. While these cables are applicable to the great majority of cable installations that are on grounded systems, they shall be permitted to be used also on other systems for which the application of cables is acceptable, provided the above clearing requirements are met in completely de-energizing the faulted section.

2. 133 Percent Insulation Level. This insulation level corresponds to that formerly designated for ungrounded systems. Cables in this category shall be permitted to be applied in situations where the clearing time requirements of the 100 percent level category cannot be met and yet there is adequate assurance that the faulted section will be de-energized in a time not exceeding 1 hour. Also, they shall be permitted to be used in 100 percent insulation level applications where additional insulation is desirable.

3. 173 Percent Insulation Level. Cables in this category shall be permitted to be applied under all of the following conditions:

(1) In industrial establishments where the conditions of maintenance and supervision ensure that only licensed electrical practitioner or non licensed electrical practitioner under the supervision of a licensed electrical practitioner service the installation
(2) Where the fault clearing time requirements of the 133 percent level category cannot be met
(3) Where an orderly shutdown is essential to protect equipment and personnel
(4) There is adequate assurance that the faulted section will be de-energized in an orderly shutdown

Also, cables with this insulation thickness shall be permitted to be used in 100 or 133 percent insulation level applications where additional insulation strength is desirable.