# Conductor Ampacity Calculation – Part Eleven

In Article " Conductor Ampacity Calculation – Part Ten ", I explained how to use the Annex B Tables included under Group#2-A “ tables for conductors installed in underground electrical duct bank” which includes:

• TABLE B.310.15(B)(2)(5) in Accordance with Figure B.310.15(B)(2)(2),
• TABLE B.310.15(B)(2)(6) in Accordance with Figure B.310.15(B)(2)(2),
• TABLE B.310.15(B)(2)(7) in Accordance with Figure B.310.15(B)(2)(2),

Today, I will explain how to use Other Annex B tables and figures.

For more information about the Second method for Conductors ampacity calculations by using Annex B Tables under engineering supervision, please review the following articles:

For more information about the first method for Conductors ampacity calculations by using Tables as provided in 310.15(B), please review the following articles:

Using Annex B tables and figures:

 Rule#1: Annex B Tables And Figures Annex B consists of many tables and figures as follows: 1- Tables: TABLE B.310.15(B)(2)(1), TABLE B.310.15(B)(2)(3), TABLE B.310.15(B)(2)(5) in Accordance with Figure B.310.15(B)(2)(2), TABLE B.310.15(B)(2)(6) in Accordance with Figure B.310.15(B)(2)(2), TABLE B.310.15(B)(2)(7) in Accordance with Figure B.310.15(B)(2)(2), TABLE B.310.15(B)(2)(8)  in Accordance with Figure B.310.15(B)(2)(2), TABLE B.310.15(B)(2)(9) in Accordance with Figure B.310.15(B)(2)(2), TABLE B.310.15(B)(2)(10) in Accordance with Figure B.310.15(B)(2)(2), TABLE B.310.15(B)(2)(11). 2- Figures: The following figures represent Underground electrical duct bank configurations: Figure B.310.15(B)(2)(1) Figure B.310.15(B)(2)(2) Figure B.310.15(B)(2)(3), Figure B.310.15(B)(2)(4), Figure B.310.15(B)(2)(5).

Annex B tables and figures, click on the link.

The above tables can be divided to groups as follows:

• Tables Group#1: tables for conductors installed in free air.
• Tables Group#2: tables for conductors installed in underground electrical duct bank tables.
• Tables Group#3: adjustment factor tables

The above figures can be divided to groups as follows

• Figures Group#2: special case figures.

Second: Tables Group#2: tables for conductors installed in underground electrical duct bank or directly Buried tables.

This tables group can be divided to two sub-groups as follows:

Tables Group#2-A: tables for conductors installed in underground electrical duct bank which includes:

• TABLE B.310.15(B)(2)(5) in Accordance with Figure B.310.15(B)(2)(2),
• TABLE B.310.15(B)(2)(6) in Accordance with Figure B.310.15(B)(2)(2),
• TABLE B.310.15(B)(2)(7) in Accordance with Figure B.310.15(B)(2)(2),

Tables Group#2-B: tables for conductors directly Buried in earth which includes:

• TABLE B.310.15(B)(2)(8) in Accordance with Figure B.310.15(B)(2)(2),
• TABLE B.310.15(B)(2)(9) in Accordance with Figure B.310.15(B)(2)(2),
• TABLE B.310.15(B)(2)(10) in Accordance with Figure B.310.15(B)(2)(2),

1.1 Tables Group#2-B Construction:

For example, Table B.310.15(B)(2)(8) Ampacities of Two or Three Insulated Conductors, Rated 0 Through 2000 Volts, Cabled Within an Overall (Two- or Three-Conductor) Covering, Directly Buried in Earth, Based on Ambient Earth Temperature of 20°C (68°F), Electrical Duct Arrangement in Accordance with Figure B.310.15(B)(2)(2), 100 Percent Load Factor, Thermal Resistance (Rho) of 90.

 Fig (1)

Table B.310.15(B)(2)(8) consists of: (see fig.1)

 1.1.A Conditions For Table Application These conditions are existing in the table description at the top of the table, and in table  B.310.15(B)(2)(8) , these conditions are: Two or Three Insulated Conductors  Cabled Within an Overall (Two- or Three-Conductor) Covering, Directly Buried in Earth, Electrical Duct Arrangement in Accordance with Figure B.310.15(B)(2)(2), Conductors  Rated 0 Through 2000 Volts, Ambient Earth Temperature of 20°C (68°F). 100 Percent Load Factor, Thermal Resistance (Rho) of 90.

 1.1.B Conductor Material Sections Two main Sections for conductor material type are existing: One for copper, One for aluminum or copper-clad aluminum conductors.

 1.1.C Cables Installation Configurations Each of The two main sections for conductor material types is divided into Two Cable Installation Configurations: 1 Cable (Fig. B.310.15(B)(2)(2), Detail 5), 2 Cables (Fig. B.310.15(B)(2)(2), Detail 6). Noting that: Each Cable Installation Configuration is applied for Two Conductor Temperatures 60°C (140°F) for Type UF insulation material  and 75°C (167°F) for Types RHW, THHW, THW, THWN, XHHW, USE.

 1.1.D Conductor Sizes Columns Two Columns for conductor sizes range from 8 AWG to 1,000 kcmil: The left one beside copper conductors column is for copper conductors sizes, The right one beside aluminum or copper-clad aluminum conductors column is for aluminum or copper-clad aluminum conductors sizes.

 1.1.E Correction Factors for Ambient Temperature Under each main Material Section; copper and aluminum/copper-clad aluminum conductors, there is a section of Correction Factors for Ambient Temperature Which gives the value of a correction factor for Ambient Temperature based on the Actual Ambient temperature columns in the right and left of this section.

Other tables included in Group#2-B have the same construction as explained above for table B.310.15(B)(2)(8) but of course they will differ as per the following table:

 Table B.310.15(B)(2)(8) Table B.310.15(B)(2)(9) Table B.310.15(B)(2)(10) Conditions for table application Two or Three Insulated Conductors  Cabled Within an Overall (Two- or Three-Conductor) Covering, Directly Buried in Earth Three Triplexed Single Insulated Conductors, Directly Buried in Earth Three Single Insulated Conductors, Directly Buried in Earth Number of Electrical Cables/ Circuits 1 and 2 Cable 1 and 2 Circuit 1 and 2 Circuit Allowable Cable Installation Configurations (see fig.2) Detail 5 and 6 Detail 7 and 8 Detail 9 and 10 Allowable Conductor Sizes from 8 AWG to 1,000 kcmil from 8 AWG  to 1,000 kcmil from 8 AWG  to 2,000 kcmil Insulation Material Types Types UF, RHW, THHW, THW, THWN, XHHW, USE Types UF, USE Types UF, USE

 Fig (2)

1.2 Notes for Tables Group#2-A:

 Note#1 All tables included under group#2-B are used in Accordance with Cable installation configurations included in Figure B.310.15(B)(2)(2) (see fig.2)

Note#2

Only the conductors/cables with the following insulation materials are used under tables of group#2-A:

 Table B.310.15(B)(2)(8) Table B.310.15(B)(2)(9) Table B.310.15(B)(2)(10) Insulation Material Types Types UF, RHW, THHW, THW, THWN, XHHW, USE Types UF, USE Types UF, USE

Don’t apply tables group#2-B for conductors/cables with other insulation materials listed above.

 Note#3 Apply Ambient temperature correction factors if the actual earth ambient temperature not 20°C (68°F) and as per the Correction Factors section included in each table of group#2-B

 Note#4 Minimum burial depths to top cables shall be in accordance with NEC Section 300.5. Maximum depth to the top of direct buried cables shall be 900 mm (36 in.)

 Note#5 In Table B.310.15(B)(2)(8), For ampacities of Type UF cable in underground electrical ducts, multiply the ampacities shown in the table by 0.74.

1.3 How to use these Tables group#2-B

Step#1: Determine the proper table to use based on the existing wiring method conditions
For example, if we have Three Triplex Insulated Conductors 2 AWG Copper , UF Directly Buried in Earth based on an earth ambient temperature of 30° C (86° F), which table we will use; Table B.310.15(B)(2)(8) or Table B.310.15(B)(2)(9) or Table B.310.15(B)(2)(10)? (See fig.3).

 Fig (3)

• Yes, it is table B.310.15(B)(2)(9),
• Why it is not Table B.310.15(B)(2)(8) because we have three Triplex Insulated Conductors not Three Insulated Conductors Cabled Within an Overall Covering
• Why it is not Table B.310.15(B)(2)(10) because we have Three Triplex Insulated Conductors not Three single Insulated Conductors.

 Fig (4)

Step#2: Determine the proper section in the selected table based on the conductor material type (Copper – Aluminum or Copper Clad Aluminum) (see fig.4)
In same example above, because this is a copper conductor, we will use the section in the left side of table B.310.15(B)(2)(6).

(see fig.4)

In the table section selected above, move down to the given conductor size, which is 2 AWG in our example, the amapcity value are existing in the 2 AWG Row.

Now, move to the right in the 2AWG row until you reach the column for detail#7 (1 circuit) configuration, move to the Column Type UF, the reading will be in this column.

Step#4: Now read the amapcity of the conductor, you should read 153.

In the next Article, I will explain how to use Other Annex B tables and figures groups. Please, keep following.