In Article " Conductor Ampacity Calculation – Part Ten ", I explained how to use the Annex B Tables included under Group#2A “ 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:
2 Figures:
The following
figures represent Underground electrical duct bank configurations:

To download a PDF copy of 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#1: adjustment figure for Thermal Resistivity and Load Factor.
 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 subgroups as follows:
Tables Group#2A: 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#2B: 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#2B 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 ThreeConductor) 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:

1.1.B Conductor Material Sections
Two main Sections for
conductor material type are existing:

1.1.C Cables Installation Configurations
Each of The two main sections
for conductor material types is divided into Two Cable Installation
Configurations:
Noting that:

1.1.D Conductor Sizes Columns
Two Columns for conductor
sizes range from 8 AWG to 1,000 kcmil:

1.1.E Correction Factors for Ambient Temperature
Under each main Material
Section; copper and aluminum/copperclad 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#2B 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 ThreeConductor)
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


1.2 Notes for Tables Group#2A:
Note#1
All tables included under
group#2B 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#2A:
Don’t apply tables group#2B
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#2B

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#2B
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).
Step#3: Reading the Ampacity Value (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.
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