NEC Practice Test (Code)

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What conductor size is needed for a single-family housing unit with an estimated load of 220 amps and a maximum unbalanced neutral load of 110 amps?

Correct! Wrong!

Service conductor for 225 Amperes load = 3/0 AWG neutral conductor for unbalanced load 110 = 3 AWG

What size service conductors are needed for a 190 A calculated load in a dwelling? The service disconnect breaker has a 200-amp rating.

Correct! Wrong!

Answer : 2/0 AWG Note : Service conductors that supply individual dwelling unit or single dwelling unit can have ampacity rating of 83% of service disconnect. The conductor ampacity for 200 A service disconnect = 0.83 * 200 = 166 amperes Refer : NEC Table 310.15(B)(16) 2/0 AWG with ampacity 175 amperes ( 750 C) is suitable as service conductor

If the raceway contains four 1/0 THWN conductors, what is the ampacity of a 1/0 THWN conductor in a dry location at a temperature of 1040 F?

Correct! Wrong!

The conductor ampacity of 1/0 THWN in dry location ( 900C) = 170 amperes ( NEC Table 310.15(B)(16)) Ambient temperature correction factor at 1080F = 0.91 ( NEC Table 310.15(B)(2)) Raceway conductor bundle adjustment factor for 4 conductors = 0.8 ( NEC Table 310.15(B)(3)(a)) corrected ampacity = 170 * 0.8*0.91 = 124 amperes

The branch conductor's ampacity, which supplies power to the motor with an FLC of 25 amperes, is

Correct! Wrong!

Conductor ampacity = 125% of FLC = 1.25 * 25 = 31.25 amperes

The connected load of a single family dwelling unit is 4000 VA. The calculated demand load is which of the following?

Correct! Wrong!

First 3000 VA the demand factor is 100% = 3000 * 100 % = 3000 VA remaining (4000-3000) = 1000 ( demand factor = 35%) = 1000 * 0.35 = 350 VA total demand load = 3000 + 350 = 3350 VA

The voltmeter at one end of the feeder reads 240 volts. What is the volt-minimum meter's reading voltage at the outlet of lighting loads?

Correct! Wrong!

The maximum voltage drop in feeder is 3 % the voltmeter reading = 240 – 0.03 * 240 = 240 – 7.2 = 232.8 volts

For a 4200 W, 240 V electric water heater connected in a building, what is the maximum size over current device required?

Correct! Wrong!

Protection rating for an electric water heater should be less than 150% of the rating of device. Protection size = 4200 / 240 * 1.5 Protections size = 26.25 A The nearest next size over current device is 30 A.

The entry points of underground ducts or conduits into the building must be sealed.

Correct! Wrong!

These must be sealed to prevent the entry of gases or moisture in to the building.

A 2/0 THWN conductor is placed in a dry area at a temperature of 450 degrees Celsius. What is the conductor's corrected ampacity?

Correct! Wrong!

Ampacity of 2/0 THWN conductor in dry location = 195 A ( NEC Table 310.15 (B)(16)) Correction Ampacity at ambient temperature 450 C = 0.87 (NEC Table 310.15(B)(2)) Corrected Ampacity of conductor = 0.87 * 195 = 170 Amperes

In a 3/4 EMT trade size, how many 10 AWG RHH conductors may be installed?

Correct! Wrong!

Total 6 10 AWG RHH conductors can be installed in trade size ¾ EMT.

What is the adjustment ampacity of a 3/0 THWN conductor in a wet location with an ambient temperature of 1080F? There are four 3/0 THWN conductors in the raceway.

Correct! Wrong!

3/0 THWN conductor ampacity in wet location (750C) = 175 Amperes ( NEC 310.15(B)(16)) Ambient temperature correction factor at 1080F = 0.85 ( NEC 310.15(B)(2)) raceway conductor bundle adjustment factor for 4 conductors= 0.8 ( NEC 310.15(B)(3)(a)) The conductor ampacity = 175 * 0.85 * 0.8 = 119 Amperes

A cord-and-plug-attached appliance is linked to a 25 ampere branch circuit. What is the maximum ampere rating that the appliance can handle?

Correct! Wrong!

Cord and plug connected equipment shall not exceed 80 percent of branch circuit rating 25 * 0.8 = 20 amperes

The capacity of the conductor is 150 amperes. If five conductors are placed in a flexible cord, what is the maximum conductor ampacity allowed for each conductor?

Correct! Wrong!

For 5 conductors in flexible cord allowed ampacity percentage = 80 % of rated amapcity Allowed amapcity of each conductor with 150 Ampere rating = 150 * 0.8 = 120 amperes.

Which of the following is the minimum size of a single supply-side bonding jumper for three metal raceways with 300 kcmil service conductors each?

Correct! Wrong!

NEC Table 250.102(C)(1) For over 3/0 AWG and 350 kcmil the required bonding jumper size is 2 AWG

On a 15 amp branch circuit operating at 120 volts, what is the maximum number of receptacles that can be installed?

Correct! Wrong!

P = 120 * 15 = 1800 Number of receptacles = 1800 / 180 = 10 receptacles

A 1/0 THWN in a wet location has a rated ampacity of 150 amperes. If the same conductor is used at a temperature of 400 degrees Celsius. What is the corrected ampacity?

Correct! Wrong!

Temperature correction factor of 1/0 THWN Conductor for 40-750 C = 0.88 The corrected ampacity = 0.88 * 150 = 132 amperes

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