Lesson 2: Determining Conductor Ampacity Flashcards
Twenty-one 10 AWG THHW aluminum current-carrying conductors are installed in the same conduit in a wet location area with a 30°C ambient temperature. What is the ampacity of each conductor? Do not apply 220.5(B).
13.5 A
Note: See NEC 310.15(C)(1) and 310.16.
Table 310.16
10 AWG THHW AL = 30 A, THHW insulation installed in a wet location is 75°C insulation. See Table 310.4.
Adjustment Factor
Table 310.15(C)(1)
21 Current-Carrying Conductors = 0.45
30 × 0.45 = 13.5 A
Twelve 12 AWG THHN copper conductors are installed in a one-inch electrical metallic tubing, Type EMT in an ambient temperature of 32°C. These twelve conductors are comprised of three 4-wire multiwire branch circuits. The multiwire branch circuits are supplied by a 4-wire, 3-phase, wye-connected system. The neutral conductor in each of these multiwire branch circuits carries only the unbalanced current from the other conductors in each respective multiwire branch circuit. What is the ampacity of each of the 12 AWG conductors? Do not apply 220.5(B).
20.16 A
Note: See NEC 310.15(B)(1), 310.15(C)(1), 310.15(E), and 310.16.
Table 310.16
12 AWG THHN = 30 A
Correction Factor
Table 310.15(B)(1)(1)
THHN Insulation at 32°C = 0.96
Adjustment Factor
Table 310.15(C)(1)
9 Current-Carrying Conductors = 0.7
30 × 0.96 × 0.7 = 20.16 A
Which of the following is NOT an adjustment factor requirement specific to 310.15(C)(1)?
a.
Where conductors of different systems, such as control circuits and power circuits, are installed in common raceways or cables, only the power and lighting conductors for branch circuits, feeders, and services need to be counted.
b.
Where current-carrying conductors are assembled as a set of parallel conductors, each conductor is counted separately.
c.
Where the number of current-carrying conductors in a raceway or cable exceeds three, or where a single conductor or multiconductor cable is installed without maintaining spacing for a continuous length longer than 24 inches and is not installed in a raceway, the ampacity of each conductor must be reduced by the factors of Table 310.15(C)(1).
d.
All of the above are adjustment factor requirements specific to 310.15(C)(1).
d.
All of the above are adjustment factor requirements specific to 310.15(C)(1)
Twelve 12 AWG THWN-2 copper conductors are installed in a one-inch electrical metallic tubing, Type EMT in an ambient temperature of 32°C. These twelve conductors are comprised of three 4-wire multiwire branch circuits. The multiwire branch circuits are supplied by a 4-wire, 3-phase, wye-connected system. The major portion of the load for each multiwire branch circuit consists of nonlinear loads. What is the ampacity of each of the 12 AWG conductors? Do not apply 220.5(B)
14.4 A
Note: See NEC 310.15(B)(1), 310.15(C)(1), 310.15(E), and 310.16.
Table 310.16
12 AWG THWN-2 = 30 A
Correction Factor
Table 310.15(B)(1)(1)
THWN-2 Insulation at 32°C = 0.96
Adjustment Factor
Table 310.15(C)(1)
12 Current-Carrying Conductors = 0.5
30 × 0.96 × 0.5 = 14.4 A
Which of the following conductors would be considered a current-carrying conductor as per 310.15(C)(1)?
a.
A control circuit conductor
b.
A neutral conductor that carries only the unbalanced current from other conductors of the same circuit
c.
A spare or unused conductor in a raceway
d.
An equipment grounding conductor
c.
A spare or unused conductor in a raceway
Note: See NEC 310.15(C)(1), 310.15(E), and Note to Table 310.15(C)(1).
The correct answer is: A spare or unused conductor in a raceway
A 4-conductor, metal-clad cable is used as the feeder for a 120/208-volt panel supplying discharge lighting. The 3/0 AWG copper conductors have 90°C insulation and the cable is installed in an area with an ambient temperature of 42°C. What is the ampacity of each 3/0 AWG conductor? Do not apply 220.5(B).
156.6 A
Note: See NEC 310.15(B)(1), 310.15(C)(1), and 310.16.
Table 310.16
3/0 AWG 90°C = 225 A
Correction Factor
Table 310.15(B)(1)(1)
90°C Insulation at 42°C = 0.87
Adjustment Factor
Table 310.15(C)(1)
4 Current-Carrying Conductors = 0.8
225 × 0.87 × 0.8 = 156.6 A
Two 10 AWG THWN, three 2 AWG THWN, and two 12 AWG THWN copper current-carrying conductors are installed in the same conduit in an area with an ambient temperature of 30°C. What is the ampacity of the 2 AWG conductors? Do not apply 220.5(B).
80.5 A
Note: See NEC 310.15(C)(1) and 310.16.
Table 310.16
2 AWG THWN = 115 A
Adjustment Factor
Table 310.15(C)(1)
7 Current-Carrying Conductors = 0.7
115 × 0.7 = 80.5 A
A 4-conductor (two circuit), Type MC, metal-clad cable is used to supply two dedicated 20-ampere computer circuits within an office building. The cable is comprised of two ungrounded conductors, two grounded conductors, and a green equipment grounding conductor. The 12 AWG copper conductors have 90°C insulation, and the cable is installed in an area with an ambient temperature of 32°C. What is the ampacity of each 12 AWG conductor? Do not apply 220.5(B).
23.04 A
Note: See NEC 310.15(B)(1), 310.15(C)(1), and 310.16.
Table 310.16
12 AWG 90°C = 30 A
Correction Factor
Table 310.15(B)(1)(1)
90°C Insulation at 32°C = 0.96
Adjustment Factor
Table 310.15(C)(1)
4 Current-Carrying Conductors = 0.8
30 × 0.96 × 0.8 = 23.04 A
which of the following installations would NOT require the application of Table 310.15(C)(1)?
a. A conduit containing a 3-phase feeder run in parallel where 2 conductors per phase are used
b. A conduit containing 12 control circuit conductors and 6 motor circuit conductors.
c. A metal wireway that contains 25 ungrounded branch circuit conductors
d. Three 12-2 NM, nonmetallic cables bundled together for 30 degrees
c. A metal wireway that contains 25 ungrounded branch circuit conductors
Note: See NEC 310.15(C)(1) and 376. 22(B)
which of the following neutral conductors would be required to be counted as a current-carrying conductor per 310.15(E)?
a.
The neutral conductor of a 12-3 Type MC, metal-clad cable installed in an office building supplying 2 circuits of discharge lighting where the service is rated 120/208-volt 3-phase.
b.
The neutral conductor of a 12-3 Type NM, nonmetallic cable installed in a dwelling unit supplying receptacle outlets in a kitchen where the service is rated 120/240-volt single-phase.
c.
The neutral conductor of a 12-4 Type MC, metal-clad cable installed in an office building supplying 3 circuits of electric space heating equipment; the service is rated 120/208-volt 3-phase.
d.
The neutral conductor of a 14-3 Type NM, nonmetallic cable installed in a dwelling unit supplying LED lighting where the service is rated 120/240-volt single-phase.
a.
The neutral conductor of a 12-3 Type MC, metal-clad cable installed in an office building supplying 2 circuits of discharge lighting where the service is rated 120/208-volt 3-phase.
Three 3-phase motors are supplied with nine 8 AWG THHN copper conductors in the same rigid metal conduit, type RMC, in an ambient temperature of 30 degrees Celsius. What is the ampacity of each current carrying conductor?
38.5 A
Note: See NEC 310.15(C)(1) and 310.16
8 AWG THHN = 55 amps
Adjustment factor
310.15(C)(1)
9 current carrying conductors = 0.7
55*0.7= 38.5 A
Three 12 AWG THWN and three 14 AWG TW copper current carrying conductors are installed in the same rigid metal conduit, type RMC, in an area with an ambient temperature of 30 degrees celsius. what is the ampacity of the 12 AWG conductors?
20 A
Note: see NEC 310.15(C)(1) and 310.16
12 AWG THHN = 30 Amps
Adjustment factor
table 310.15(C)(1)
6 current carrying conductors = 0.8
30x0.8=24 A
Twelve 10 AWG THHN copper current-carrying conductors are installed in a 1 1/2” conduit, type RMC, in an area with an ambient temperature of 40 degrees celsius. what is the ampacity of each conductor?
18.2 A
Note: see NEC 310.15(C)(1) and 310.16
10 AWG THHN = 40 Amps
correction factor
table 310.15(B)(1)(1)
THHN insulation at 40 degrees C = 0.91
Table 310.15(C)(1)
12 current carrying conductors = 0.5
40x0.91x0.5=18.2 A
Thirty-Two 12 AWG THHN copper current-carrying conductors are installed in ambient temperature of 45 degrees C. What is the ampacity of each conductor?
10.44 A
Note: see NEC 310.15(C)(1) and 310.16
12 AWG THHN = 30 Amps
correction factor
table 310.15(B)(1)(1)
THHN insulation at 45 degrees C = 0.87
Table 310.15(C)(1)
32 current carrying conductors = 0.4
30x.87x.4=10.44 A
Two “A” phase conductors, two “B” phase conductors, and two neutrals are installed as two 3-wire multiwire branch circuits of a 120/208-volt system. They are installed in electrical metallic tubing, Type EMT in an ambient temperature of 30°C. The conductors are 10 AWG XHHW copper. What is the ampacity of each of the current-carrying conductors? Do not apply 220.5(B).
32 A
Note: see NEC 310.15(C)(1) and 310.16
10 AWG XHHW = 40 Amps
Adjustment factor
table 310.15(C)(1)
6 current carrying conductors = 0.8
40x.8= 32 A
Two 3-phase, 4 wire multiwire branch circuits supply LED lighting loads from a 3-phase, 4 wire, wye system. The branch circuits consist of eight 10 AWG THWN copper conductors installed in electrical metallic tubing, type EMT in an ambient temperature of 86 degrees F. what is the ampacity of the 10 AWG conductors in this application?
24.5 A
Note: see NEC 310.15(C)(1), 310.15(E) and 310.16
10 AWG THWN = 35 Amps
Adjustment factor
table 310.15(C)(1)
8 current carrying conductors = 0.7
35x.7= 24.5 A
The neutral conductors of two 2-wire, 120-volt, single-phase circuits are installed in the same raceway supplying two household refrigerators are considered to be current-carrying conductors when applying the provisions of table 310.15(C)(1).
true or false
True
