Lesson 1: Beginning to Calculate Conductor Ampacity

Question 1

The ampacities specified in Table 310.16 apply where which of the following conditions exist?

a. Conductors are rated 0 V through 2,000
b. Conductors are rated 60°C (140°F), 75°C (167°F), or 90°C (194°F)
c. There are not more than three current-carrying conductors.
d. Wiring is installed in a 30°C (86°F) ambient temperature
e. All of the above
f. None of the above

Answer 1

e. all of the above

CODE REF: 310.16

Question 2

Which formula matches the wording shown?
The secondary conductors shall have an ampacity that is not less than the value of the primary-to-secondary voltage ratio multiplied by one-tenth of the rating of the overcurrent device protecting the primary of the transformer.

Answer 2

needs picture

Question 3

Which formula matches the wording taken from the Code and these directions?

The secondary conductors shall have an ampacity that is not less than the value of the primary-to-secondary voltage ratio multiplied by one-tenth of the rating of the overcurrent device protecting the primary of the transformer.

Transpose the formula to find maximum OCPD for a given conductor size.

Answer 3

Question 4

For the following voltages, indicate whether they are listed as nominal system voltages specified for use in calculations by the Code.
220 V
115 V
440 V
120 V
135 V
480 V
347 V
240 V

Answer 4

220 V
No
115 V
No
440 V
No
120 V
Yes
135 V
No
480 V
Yes
347 V
Yes
240 V
Yes

Question 5

Three 3/0 AWG THHN copper conductors are installed in rigid nonmetallic conduit, Type PVC, with a 90°C rating, in an ambient temperature of 150°F. What is the ampacity of the three current-carrying conductors? Round to the nearest ampere.

Answer 5

131 A

Question 6

Match the formula with the Code. NOTE: The formulas may be transposed to solve for a specific variable. Two of the formulas are not correctly formed; label them as Not Valid.
cont. load ≤ table value × 0.8
OCPD ≥ non. cont. + 1.25 × cont.
max load ≤ table value × corr. factor
Load ≤ table value × adjustment factor
OCPD > FLA × 1.25

Answer 6

cont. load ≤ table value × 0.8
210.19(A)
OCPD ≥ non. cont. + 1.25 × cont.
210.20(A)
max load ≤ table value × corr. factor
Table 310.15(B)(1)(1)
240.21(C)(6)(1)
Correct
240.21(C)(2)(4)
Load ≤ table value × adjustment factor
Table 310.15(C)(1)
240.21(C)(2)(4)
OCPD > FLA × 1.25
Not valid

NEEDS PICTURES

NOT ON TEST

Question 7

One single 1/0 AWG THW aluminum conductor is installed in free air in an ambient temperature of 86°F. What is the ampacity of the current-carrying conductor?

Answer 7

180 A

Question 8

Ampacity calculations with respect to the conductor should focus on the maximum operating temperature of which part of the conductor?

a.
Conduit type
b.
Inner conducting metal
c.
Insulation
d.
Outer protective coating

Answer 8

c.
Insulation

Question 9

Which of the following is NOT part of the definition of ampacity?
a. Able to carry current intermittently
b. Maximum current, in amperes
c. Under the conditions of use
d. Without exceeding its temperature rating

Answer 9

a. Able to carry current intermittently

CODE REF: 100

Question 10

Three 3/0 AWG THHN copper conductors are installed in rigid nonmetallic conduit, Type PVC, with a 90°C rating, in an ambient temperature of 86°F. What is the ampacity of the three current-carrying conductors?

Answer 10

225 A

Question 11

Match the following word statements in the correct order to obtain the correct definition for ampacity.
1.
2.
3.
4.
5.
6.

that a conductor can carry continuously
in amperes
under the conditions of use
The maximum current
its temperature rating
without exceeding

Answer 11

1. The maximum current
2. in amperes
3. that a conductor can carry continuously
4. under the conditions of use
5. without exceeding
6. its temperature rating

Question 12

Match the formula with the Code. NOTE: The formulas may be transposed to solve for a specific variable. Three of the formulas are not correctly formed; label them as Not Valid.
min. amp. ≥ non. cont. + 1.25 cont.
Continuous load ≤ OCPD × 0.8

Answer 12

needs picture

Question 13

One single 8 AWG THWN-2 copper conductor is installed in free air in an ambient temperature of 50°C. What is the ampacity of the current-carrying conductor? Round to the nearest ampere.

Answer 13

66 A

Question 14

Conductor heating originates from many sources. Match each description to the appropriate heating term.

Environment or ambient air temperature which may vary along the conductor’s length or may vary during the time of day.

Heat generated by current flowing through adjacent load-carrying conductors, which adds to the ambient heat and impedes the heat dissipation process within the conduit or cable assembly.

Heat generated by the load current flowing in the metal conductor material due to the natural resistance of the conductor.

Retained heat due to the inability of the surrounding media to dissipate heat.

Answer 14

Environment or ambient air temperature which may vary along the conductor’s length or may vary during the time of day. → Area Heat

Heat generated by current flowing through adjacent load-carrying conductors, which adds to the ambient heat and impedes the heat dissipation process within the conduit or cable assembly. → Adjacent Conductor Heat

Heat generated by the load current flowing in the metal conductor material due to the natural resistance of the conductor. → Load Current Heat

Retained heat due to the inability of the surrounding media to dissipate heat. → Ability to Cool Down or Dissipate Heat

Question 15

Table 310.17 applies to the single insulated conductor installed in free air where the heat generated within the conductor can be more easily dissipated than where the same insulated conductor is enclosed in a raceway or cable jacket.
a. True
b. False

Answer 15

True

CODE REF: 310.17

Question 16

Definitions for terms found in a single article will have the article number in parentheses following the definition.
a. True
b. False

Answer 16

True

CODE REF: 100

Question 17

Which formula matches the wording taken from the Code and these directions?

The ampacity of conductors that connect a capacitor to the terminals of a motor or to motor circuit conductors shall not be less than one-third the ampacity of the motor circuit conductors.

Transpose the formula to find maximum motor circuit ampacity for a given capacitor conductor size.

a.
ampacity ≤ 1/3 × motor conductor ampacity

b.
cap. cond. ampacity ≥ 1/3 × motor cap. cond. ampacity

c.
motor circ. cond. ampacity ≤ 3 × cap. cond. ampacity

d.
cap. cond. ampacity = 1/3 × motor cap. cond. ampacity

Answer 17

c.
motor circ. cond. ampacity ≤ 3 × cap. cond. ampacity

Question 18

Two 8 AWG THWN-2 copper conductors are installed in rigid metal conduit, Type RMC, in an ambient temperature of 86°F. What is the ampacity of the two current-carrying conductors? Round to the nearest ampere.

Answer 18

55 A

Question 19

Which of the following statements represents the purpose of the NEC?
a. As an instruction manual for untrained persons
b. The practical safeguarding of persons and property from hazards arising from the use of electricity
c. To be a design specification guide
d. All of the above

Answer 19

b. The practical safeguarding of persons and property from hazards arising from the use of electricity

CODE REF: 90.2(A)

Question 20

One single 1/0 AWG THW aluminum conductor is installed in free air in an ambient temperature of 104°F. What is the ampacity of the current-carrying conductor? Round to the nearest ampere

Answer 20

158 A

Question 21

Match the term or phrase to the Code section that would most likely apply.

Conductor Material Type
Definitions
Practical Safeguarding
Voltages used for calculating loads

Answer 21

Conductor Material Type
110.5
Definitions
100
Practical Safeguarding
90.2
Voltages used for calculating loads
220.5

Question 22

Which of the following statements are true with respect to the purpose of the National Electrical Code (NEC)?

a.
The NEC is not intended as an instruction manual for untrained persons.

b.
The NEC is not intended to be a design specification guide.

c.
The purpose of the NEC is the practical safeguarding of persons and property from hazards arising from the use of electricity.

d.
All of the above.

Answer 22

d. all of the above

Question 23

Which formula matches the wording shown?

The ampacity of capacitor circuit conductors shall not be less than 135% of the rated current of the capacitor.

a.
ampacity ≤ 1.35 × rated current of capacitor

b.
ampacity ≥ 1.35 × rated current of capacitor

c.
ampacity = 1.35 × rated current of capacitor

Answer 23

b.
ampacity ≥ 1.35 × rated current of capacitor

Question 24

Definitions for terms found in a single article will NOT typically be shown in Article 100.
Select one:
True
False

Answer 24

False

Question 25

Definitions for terms found in multiple articles will have an article number in parentheses following the definition. a. True b. False

Answer 25

False CODE REF: 100

Question 26

Two 8 AWG THWN-2 copper conductors are installed in rigid metal conduit, Type RMC, in an ambient temperature of 95°F. What is the ampacity of the two current-carrying conductors? Round to the nearest ampere.

Answer 26

53 A

Question 27

Which formula matches the wording taken from the Code and these directions? The ampacity of capacitor circuit conductors shall not be less than 135% of the rated current of the capacitor. Transpose the formula to solve for maximum rated current of capacitor allowed for a given conductor size. a. ampacity ≤ 1.35 × rated current of capacitor b. c.

Answer 27

needs picture

Question 28

Three 4 AWG THHN copper conductors are installed in electrical metallic tubing, Type EMT, in an ambient temperature of 30°C. What is the ampacity of the three current-carrying conductors? Round to the nearest ampere.

Answer 28

95 A

Question 29

Match the formula with the Code. NOTE: The formulas may be transposed to solve for a specific variable. Three of the formulas are not correctly formed; label them as Not valid. min. amp. ≥ non. cont. + 1.25 cont Continuous load ≤ OCPD × 0.8 OCPD > FLA × 1.25

Answer 29

needs picture

Question 30

One single 8 AWG THWN-2 copper conductor is installed in free air in an ambient temperature of 30°C. What is the ampacity of the current-carrying conductor? Round to the nearest ampere.

Answer 30

80 A

Question 31

Match the term or phrase to the Code section that would most likely apply. Conductor Sizes Reconditioned Equipment Answer Rounding fractions of an ampere Units of Measurement

Answer 31

Conductor Sizes 110.6 Reconditioned Equipment 240.2 Rounding fractions of an ampere 220.5 Units of Measurement 90.9

Question 32

Which formula matches the wording taken from Code section 460.8(A)? a. ampacity < 1/3 motor circuit conductor ampacity b. ampacity ≤ 1/3 motor conductor ampacity c. ampacity ≥ 1/3 motor circuit conductor ampacity

Answer 32

c. ampacity ≥ 1/3 motor circuit conductor ampacity

Question 33

Three 1/0 AWG THW aluminum conductors are installed in rigid metal conduit, Type RMC, in an ambient temperature of 104°F. What is the ampacity of the three current-carrying conductors? Round to the nearest ampere.

Answer 33

106 A

Question 34

Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ? . a. ampacity adjustment b. correction c. both a. and b. d. none of the above

Answer 34

c. both a. and b. CODE REF: 110.14(C)

Question 35

Which formula matches the question below and these directions? What is the maximum fuse size for a transformer with a 31.25-ampere full load current rating? Use Table 450.3(B) using primary only protection. a. OCPD ≤ FLA × 1.25 b. OCPD ≥ FLA × 1.25 c. OCPD > FLA × 1.25 d. OCPD = FLA × 1.25

Answer 35

a. OCPD ≤ FLA × 1.25

Question 36

Multiple tables are needed for ampacity calculations. Match the intended use listed below to the appropriate table. Ampacities of Insulated Conductors in Raceway, Cable, or Earth (Directly Buried) Ampacities of Single-Insulated Conductors in Free Air Conductor Constructions and Applications Single-Phase Dwelling Services and Feeders

Answer 36

Ampacities of Insulated Conductors in Raceway, Cable, or Earth (Directly Buried) Table 310.16 Ampacities of Single-Insulated Conductors in Free Air Table 310.17 Conductor Constructions and Applications Table 310.4(1) Single-Phase Dwelling Services and Feeders Table 310.12(A)

Question 37

Which of the following is part(s) of the definition of ampacity? a. Able to carry current continuously b. Maximum current, in amperes c. Under the conditions of use d. Without exceeding its temperature rating e. All of the above

Answer 37

e. all of the above

Question 38

Three 1/0 AWG THW aluminum conductors are installed in rigid metal conduit, Type RMC, in an ambient temperature of 86°F. What is the ampacity of the three current-carrying conductors? Round to the nearest ampere.

Answer 38

120 A

Question 39

Throughout the NEC, conductor sizes are expressed in ? or ? . (Pick two.) a. American Wire Gauge (AWG) b. amperes c. circular mils d. feet e. square inches

Answer 39

a. American Wire Gauge (AWG) & c. circular mils CODE REF: 110.6

Question 40

Which formula matches the wording taken from the Code and these directions? What is the maximum fuse size for a transformer with a six-ampere full load current rating? Use Table 450.3(B) using primary only protection. a. OCPD ≤ FLA × 1.67 b. OCPD ≥ FLA × 1.67 c. OCPD > FLA × 1.25

Answer 40

a. OCPD ≤ FLA × 1.67

Question 41

Two 4 AWG XHHW-2 aluminum conductors are installed in rigid metal conduit, Type RMC, in an ambient temperature of 50°C. What is the ampacity of the two current-carrying conductors? Round to the nearest ampere.

Answer 41

62 A

Question 42

Which of the following temperature ratings will NOT determine the final ampacity of a conductor? a. Conductor Insulation b. Device c. Rating of a fuse protecting the conductor d. Termination

Answer 42

c. Rating of a fuse protecting the conductor CODE REF: 110.14(C)

Question 43

tables used to calculate conductor ampacity are found in which two parts of article 310? pick 2 a. I b. II c. III d. IV e. V

Answer 43

b. II & c. III

Question 44

The NEC ___ intend to define terms which have general usage elsewhere. a. does not b. does

Answer 44

a. does not

Question 45

where the conductor material is not specified, the sizes given in the NEC shall apply to ____ conductors a. aluminum b. copper c. copper clad aluminum d. any of the above

Answer 45

b. copper CODE REF: 310.3(B) and 110.5

Question 46

if a branch circuit minimum ampacity calculation results in a value of 20.45, what is the minimum size branch circuit that would be permitted when rounding is considered?

Answer 46

20 A

Question 47

When the NEC is followed during an electrical installation, the installation will be ____. a. adequate for good services b. convenient c. efficient d. essentially fee from hazards

Answer 47

d. essentially free from hazards

Question 48

Which formula matches the wording taken from the Code and these directions? The ampacity of conductors that connect a capacitor to the terminals of a motor or to motor circuit conductors shall not be less than one-third the ampacity of the motor circuit conductors. Transpose the formula to find maximum motor circuit ampacity for a given capacitor conductor size. a. ampacity ≤ 1/3 × motor conductor ampacity b. cap. cond. ampacity ≥ 1/3 × motor cap. cond. ampacity c. motor circ. cond. ampacity ≤ 3 × cap. cond. ampacity d. cap. cond. ampacity = 1/3 × motor cap. cond. ampacity

Question 49

Three 4 AWG THHN copper conductors are installed in electrical metallic tubing, Type EMT, in an ambient temperature of 40°C. What is the ampacity of the three current-carrying conductors? Round to the nearest ampere.

Answer 49

86 A