Electrical Code Calculations, Level I (1-4)

Where types of insulated conductors from Table 310.16 are installed in other than 30°C ambient temperature areas, match the following insulated conductors to the proper ambient temperature correction factor using Table 310.15(B)(1).

1.08 .82 .88 .94

What is the ampacity of a 1 AWG THW copper conductor installed in a raceway located in an ambient temperature of 110°F? Calculate to the nearest ampere.

107 A

Three 1/0 AWG XHHW-2 aluminum conductors are installed in a rigid metal conduit, Type RMC, in an ambient temperature of 105°F. All of the conductors are current-carrying conductors. Determine the ampacity of the current-carrying conductors. Calculate to the nearest ampere.

117 A

Nine 3/0 AWG THHN aluminum conductors are installed in a three-inch RMC in an area with an ambient temperature of 35°C. Only six of the conductors are current-carrying conductors. Determine the ampacity of the 3/0 AWG conductors for this application. Calculate to the nearest ampere.

134 A

Twelve 12 AWG THHN copper conductors are installed in a one-inch 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. Determine the ampacity of each of the 12 AWG conductors. Calculate to the nearest ampere.

14 A

A 14 AWG XHHW-2 copper conductor is connected to a circuit breaker with termination temperature limitation marked (not to exceed) 60°C. What is the ampacity of this conductor now that it is connected to this circuit breaker?

15 A

Twenty 10 AWG THWN aluminum current-carrying conductors are installed in the same conduit in an ambient temperature of 30°C. Determine the ampacity of each of the current-carrying conductors. Calculate to the nearest ampere.

15 A

A 3-phase, 4-wire feeder supplies a continuous load of 75 amperes and a noncontinuous load of 75 amperes to a second floor equipment distribution switchboard.

175 A

The following conductors are installed in rigid metal conduit in an ambient temperature of 40°C. Using Table 310.18, identify the correct ampacity for these insulated conductors.

186 A 94 A 346 A 191 A

The following conductors are installed open in free air, with an ambient temperature of 40°C. Using Table 310.19, identify the correct ampacity for these insulated conductors.

198 A 142 A 629 A

The calculated load for a 3-phase, 480-volt circuit is 98 amperes. Each installation consists of three single insulated copper conductors in rigid metal conduit, Type RMC. Identify the correct copper conductor size needed for each insulation type.

1AWG 3AWG 3AWG

An existing 12 AWG TW copper conductor is connected to a new replacement circuit breaker with termination temperature limitation marked (not to exceed) 60/75°C. What is the ampacity of this conductor now that it is connected to this circuit breaker?

20 A

Twelve 12 AWG THHN copper conductors are installed in a one-inch 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. Determine the ampacity of each of the 12 AWG conductors. Calculate to the nearest ampere.

20 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 EMT in an ambient temperature of 86°F. Determine the ampacity of the 10 AWG conductors in this application. Calculate to the nearest ampere.

25 A

The minimum cubic inch (in.3) capacity of a box that contains six 14 AWG and six 12 AWG conductors is ? .

25.5

A 10 AWG THWN copper conductor is connected to a circuit breaker with termination temperature limitation marked (not to exceed) 60°C. What is the ampacity of this conductor now that it is connected to this circuit breaker?

30 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 EMT in an ambient temperature of 30°C. The conductors are 10 AWG THHN copper. What is the ampacity of each of the current-carrying conductors? Calculate to the nearest ampere.

32 A

An EMT raceway contains two 3-phase, 480-volt branch circuits. Determine the minimum standard size circuit breaker required for each of the 27 kW, 3-phase noncontinuous loads.

35 A

The following conductors are the same AWG size and have the same THW insulation, but are made up of different conductor materials. Using Table 310.16, identify the correct ampacity for these insulated conductors.

35A 30A 30A

A three-conductor 8 AWG Type NM cable is installed in an area with an ambient temperature of 94°F. Determine the ampacity of the copper circuit conductors. Calculate to the nearest ampere.

40 A

Determine the ampacity of six 8 AWG THW copper conductors installed in EMT in an ambient temperature of 30°C. All of the conductors are current-carrying conductors. Calculate to the nearest ampere.

40 A

Determine the ampacity of three 8 AWG THWN copper conductors installed in EMT in an ambient temperature of 40°C. All of the conductors are current-carrying conductors. Calculate to the nearest ampere.

44 A

Nine 4 AWG THW aluminum conductors are installed in a rigid nonmetallic conduit. Three 8 AWG THW copper conductors are installed in the same raceway for use as equipment grounding conductors. The conductors are installed in an area with an ambient temperature of 30°C, and all of the 4 AWG conductors are current-carrying conductors. Determine the ampacity of the circuit conductors. Calculate to the nearest ampere.

45 A

A box five inches square and two inches deep has a total volume of ?

50

A 3-conductor 8 AWG copper Type MC cable is installed in an area with an ambient temperature of 96°F. The conductors within the cable assembly have THHN insulation, and all three conductors are considered current-carrying conductors. Determine the ampacity of the current-carrying conductors in this application. Calculate to the nearest ampere.

50 A

Two 8 AWG XHHW-2 copper conductors are connected to a two-pole circuit breaker with termination temperature limitation marked (not to exceed) 60/75°C. What is the ampacity of these conductors now that they are connected to this two-pole circuit breaker?

50 A

Three 10 AWG FEP copper conductors are installed in a metal raceway in an area with an ambient temperature of 60°C. Using Table 310.18, calculate the ampacity of the conductors. Calculate to the nearest ampere.

56.4 A

Twelve 1 AWG THWN copper conductors are installed in a three-inch EMT in an ambient temperature of 101°F. All of the conductors are current-carrying conductors. Determine the ampacity of the 1 AWG THWN conductors for this application. Calculate to the nearest ampere.

57 A

Three single insulated conductors are installed in a conduit that is run through an area with an ambient temperature of 110°F to supply a calculated load of 65 amperes. Using Table 310.16, what is the minimum size THHN copper conductor(s) required?

6

Six 4 AWG THW copper conductors are installed in the same raceway in an ambient temperature of 30°C. All of the conductors are current-carrying conductors. Determine the ampacity of the 4 AWG current-carrying conductors. Calculate to the nearest ampere.

68 A

An EMT raceway contains two 3-phase, 480-volt branch circuits. What minimum size THHN branch circuit conductor is required for one of the circuits when it supplies a noncontinuous load of 27 kW?

8 AWG

The following conductors are installed open in free air, with an ambient temperature of 30°C. Using Table 310.17, identify the correct ampacity.

85 A 140 A 265 A 340 A

What is the ampacity of a 1 AWG THW copper conductor installed in a raceway located in an ambient temperature of 55°C? Calculate to the nearest ampere.

87.1 A

The following conductors are the same AWG size and are made up of the same copper conductor material, but have different types of insulation. Using only Table 310.16, identify the correct ampacity for these insulated conductors.

95A 115A 115A 130A

The temperature correction factor portion of Table 310.15(B)(1) indicates that as the ambient temperature increases, the ampacity of the conductor increases.

False

Identify each of the following items as either a device or a fitting.

Fitting Device Device Fitting

Identify each of the following items as either a device or a fitting.

Fitting Device Fitting Fitting

Identify and match the following conduit bodies to their correct term.

LB LL T

A conductor's ampacity is directly related to the type of insulation used on the conductor.

True

Generally, conduit bodies marked with their volume by the manufacturer are permitted to contain splices.

True

Regular 600-volt building wire will fall within the voltage rating of Table 310.16.

True

Single insulated 2 AWG THW copper conductors installed in a raceway in an ambient air temperature of 30°C will have a lower ampacity than when installed as open conductors in free air at the same ambient temperature of 30°C.

True

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.

True

Table 310.16 lists the ampacity of a 12 AWG TW copper conductor at ? , and 240.4(D)(5) limits the overcurrent protection to ? .

a. 20 A / 20 A

The two most common conductor terminal temperature ratings associated with circuit breakers and other equipment rated 100 amperes or less are ? .

a. 60°C and 75°C

Which of the following statements are permitted according to 314.23 for supporting boxes?

a. A device box is mounted and firmly fastened on a wood stud with two nails located inside the box and less than 1/4 inch from the back or ends of the box.

In general, boxes and fittings shall be securely fastened in place.

a. True 300.11(A)

The neutral conductor of a 2-wire, single-phase circuit supplying a household refrigerator is considered to be a current-carrying conductor according to the provisions of Table 310.15(C)(1).

a. True 310.15(E)(1)

A T-type conduit body with an 80 in.3 capacity is used to support a stem-mounted luminaire. The two conduits are threaded wrench tight into the T, and each of these conduits is supported within 18 inches of the conduit body. The T conduit body itself is not independently supported. This is an acceptable installation according to the Code.

a. True 314.23(E)

In addition to temperature ratings of wire terminals, a circuit breaker may be marked with another temperature rating such as 25°C or maybe even as high as 40°C. This marking most likely specifies the ? temperature.

a. ambient

Section 110.12(A) requires unused openings, other than those intended for the operation of equipment, those intended for mounting purposes, or those permitted as part of the design for listed equipment, to be ? .

a. closed

A device is defined as a unit of an electrical system, other than a conductor, that carries or ? electric energy as its principal function.

a. controls 100

The term ampacity is defined as the ? current, in amperes, that a conductor can carry continuously under conditions of use without exceeding its temperature rating.

a. maximum

A 3-phase, 4-wire feeder supplies a continuous load of 75 amperes and a noncontinuous load of 75 amperes to a second floor equipment distribution switchboard.

b. 2/0 AWG

A calculated branch-circuit load is 173 amperes. Considering all various conductor insulation types, the minimum size AWG copper conductor permitted to serve the load is ? .

b. 2/0 AWG

The calculated load for a 3-phase, 240-volt load is 196 amperes. The installation consists of three single insulated conductors in electrical metallic tubing, Type EMT. What size RHW copper conductors are needed?

b. 3/0 AWG

What is the ampacity of each 10 AWG copper conductor with 90°C insulation within a 3-conductor Type NM nonmetallic sheathed cable?

b. 30

Each conductor of a 3-conductor (3/C) armored cable (Type AC) assembly using 10 AWG insulated copper conductors with 75°C insulation has an ampacity of ? .

b. 35 A

The three most common insulated conductor temperature ratings associated with Table 310.16 are ? .

b. 60°C, 75°C, and 90°C

Which of the following statements is/are true according to 314.16(C) when applied to conduit bodies?

b. A conduit body enclosing 6 AWG conductors and smaller shall have a cross-sectional area of at least twice the cross-sectional area of the largest conduit or tubing to which it can be attached.

Control circuits are considered to be current-carrying conductors according to the provisions of Table 310.15(C)(1).

b. False 310.15(C)(1)

The equipment grounding conductor is considered to be a current-carrying conductor according to the provisions of Table 310.15(C)(1).

b. False 310.15(F)

Read the installation information for this situation and determine whether the installation is acceptable or a violation of Section 314.20. A device box for a duplex receptacle is installed 1/4 inch behind the finished surface of a wood panel wall in an office area.

b. Violation

Read the installation information for this situation and determine whether the installation is acceptable or a violation of Section 314.20. The front edge of a device box for a single-pole switch is installed in a sheetrock wall 1/2 inch behind the finished surface of the sheetrock.

b. Violation

An outlet is defined by the NEC as a point on the wiring system at which ? .

b. current is taken to supply utilization equipment 100

The neutral conductors of a 4-wire, 3-phase wye circuit, where most of the load is nonlinear and connected to ? , are considered to be current-carrying conductors according to the provisions of Table 310.15(C)(1).

b. fluorescent lighting 310.15(E)(3)

Ampacity Tables 310.18 and 310.19 apply to conductors that have an insulation rating ranging from 150°C to ? .

c. 250°C

Table 310.16 can be used when there are not more than ? single insulated current-carrying conductors installed in a raceway.

c. 3

The ampacities listed in Table 310.16 are based upon an ambient air temperature of ? .

c. 30°C (86°F)

The ampacities of Table 310.17 are for an ambient temperature of ? .

c. 30°C (86°F)

Table 310.16 lists the ampacity of a 10 AWG THHN copper conductor at ? , and 240.4(D)(7) limits the overcurrent protection to 30 amperes.

c. 40 A

The ampacities of Tables 310.18 and 310.19 are based on an ambient temperature of ? .

c. 40°C

The maximum number of 10 AWG THHN aluminum conductors permitted in a four-inch by 11/2-inch octagonal box by Table 314.16(A) is ? .

c. 6

Each conductor of a 3-conductor (3/C) service-entrance (Type SE) cable assembly using 4 AWG aluminum conductors with 90°C insulation has an ampacity of ? .

c. 75 A

The temperature rating of Type THWN insulation is ? and the temperature rating of Type THWN-2 is ? .

c. 75°C / 90°C

In which of the following situations would the basic rule of 300.15 require a box or fitting to be installed? (Note: The term "basic rule," as used here, indicates that exceptions or other conditions do not apply.)

c. Both a. and b.

From the list below, select the three Celsius and Fahrenheit insulation temperature ratings listed in Table 310.16

c. I., IV., VI.

Are THHN 90°C conductors permitted to be connected to the terminals of a circuit breaker and used at their 90°C ampacities as shown in Table 310.16?

c. Only if the circuit breaker is listed and identified for such use

The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the ? temperature rating of any connected termination, conductor, or device.

c. lowest

A fitting is defined as an accessory, such as a locknut, bushing, or other part of a wiring system, that is intended primarily to perform a(n) ? rather than an electrical function.

c. mechanical 100

The voltage rating of conductors covered by Table 310.16 is up to and including ? .

d. 2,000 V

The calculated load for a 3-phase, 240-volt load is 196 amperes. The installation consists of three single insulated conductors in electrical metallic tubing, Type EMT. What size RHW aluminum conductors are needed?

d. 250 kcmil

The Code lists the cubic inch (in.3) capacity of a four-inch square by 21/8-inch deep metal outlet box as ? .

d. 30.3 in.3

A size 1 AWG TW aluminum conductor must be replaced. What is the minimum size THHN copper conductor (of at least equal ampacity) required to fulfill this replacement?

d. 4 AWG

A calculated branch-circuit load is 178 amperes. Considering all various conductor insulation types, the minimum size AWG aluminum conductor permitted to serve the load is ? .

d. 4/0 AWG

Which of the following boxes would be permitted for the installation of three 10 AWG conductors and three 6 AWG conductors?

d. 411/16 in. × 21/8 in. square box

Determine the ampacity of three 8 AWG THWN copper conductors installed in EMT, in an ambient temperature of 30°C. All of the conductors are current-carrying conductors.

d. 50 A Table 310.16

The maximum number of 14 AWG THWN copper conductors permitted in a four-inch by 11/2-inch octagonal box by Table 314.16(A) is ? .

d. 7

Table 314.16(A) limits the number of 12 AWG conductors that may be installed in a four-inch by 11/2-inch square box to ? .

d. 9

Section 300.11 is the basic rule requiring boxes and fittings to be ? fastened in place.

d. securely

Where different temperature limitations of individual components are applied to a single circuit, the principle of the ? is often used to determine the temperature rating of the entire circuit.

d. weakest link