ELECTRIC Flashcards

The voltage waveform will lag behind the current waveform in a circuit supplying electricity to capacitive loads:

Answer: True

In Capacitor Circuit Voltage waveform lags current waveform and has leading power factor. Inductive circuit will be exactly opposite

Which of the following machines is the most efficient?

Answer: Electrical Transformer

Electrical Transformer will have higher efficiency as there is no rotating parts and airgap in the flux path involved in it. Generally efficiency of the Transformer is of the order of 95% to 99% during full load operation

During no-load operation, an induction motor's power factor will be in the range:

Answer: 0.2

Induction motor during no load condition will draw high magnetizing current. This magnetizing current will not do any useful work (rotating the load). Therefore power factor will be low during no load in Induction Motor

Conductors with _____ marked on the insulation are not allowed to be used in wet locations.

Answer: THHN

As shown in Table 310.104(A), conductors with THHN insulation are approved for use in dry and damp locations only and conductors with THWN, THHW, and THW insulation are recognized for use in dry and wet locations.

Given: The local utility company provides a 120/240 volt, single-phase electrical system to a one-family dwelling unit with a demand load of 200 amperes. What is the MINIMUM size of aluminum THW conductors required for this residence's service-entrance conductors?

Answer: 4/0 AWG

Section 310.15(B)(7)(1) permits one-family dwelling 120/240 volt, single-phase, service-entrance conductors to be sized at an ampacity of not less than 83% of the service rating. Therefore, 200 amperes x 83% = 166 amperes Table 310.15(B)(16) indicates size 4/0 AWG THW aluminum conductors with an allowable ampacity of 180 amperes should be selected for this dwelling.

The full-load current rating, in amperes, of a 150 kVA single-phase transformer with a secondary voltage of 120/240 installed in a multi-family dwelling is _____.

Answer: 625 amperes

To find the full-load current rating of the single-phase transformer apply the single-phase current formula as shown: I = (150 kVA x 1000) / 240 volts = 15,000/240 = 625 amperes

Which of the circuit breakers listed below does not have a standard ampere rating?

Answer: 75 amperes

Table 240.6(A) illustrates the standard ampere ratings for fuses and circuit breakers. A circuit breaker with an ampere rating of 75 amperes is not a standard ampere rating.

The MINIMUM length of the free conductor must be left at each junction box for splicing conductors or connecting to luminaires or devices is.

Answer: 6 inches

As per Section 300.14 at least 6 in. of free conductor is to be left at each junction box for splices or the connection of luminaires or devices. The intent of this rule is to ensure enough conductor slack for the terminal connections or splices to be made easily.

Overhead service-drop conductors must not be smaller than _____ in general.

Answer: 8 AWG copper

Section 230.23(B) requires overhead service-drop conductors to be not smaller than 8 AWG copper or 6 AWG aluminum or copper-clad aluminum. Do not get service-drop conductors, the overhead conductors between the utility electric supply system and the service point, confused with the service-entrance conductors, the conductors from the service point from the utility company to the service disconnecting means

The NEC specifies that a galvanized eye-bolt be installed NOT less than _____ above finished grade when used as a point of attachment for electrical service.

Answer: 10 ft.

The intent of Section 230.26 is to provide adequate vertical clearance of the conductors and prevent physical damage to the conductors and prevent persons from making accidental contact with the conductors which may create a shock hazard or electrocution. In no case shall the point of attachment of the service-drop conductors to be less than 10 ft. above finished grade.

Why is it required for the metallic conduits to have electrical continuity?

Answer: To establish an effective ground-fault path and facilitate the operation of the overcurrent protective device.

Electrical continuity is required for metallic conduit to establish an effective ground-fault path and facilitate the operation of the overcurrent protective device. Reference Section 250.4(A)(4) and (5).

Receptacle outlets for countertop surfaces must be located above, but not more than _____ above, the countertop or work surface in dwelling units.

Answer: 20 inches

In compliance with Section 210.52(C)(5), receptacle outlets installed for countertop or work surfaces in dwelling units may be located on or above, but not more than 20 in. above the countertop or work surface. The intent of this rule is to eliminate the use of unsightly extension cords (which reduces the amount of usable countertop space) on the countertop or work surface to supply cord-and-plug connected appliances. Also, receptacles located more than 20 inches above countertops or work surfaces may interfere with the cabinetry to be installed.

The ampacity adjustment factors for more than three (3) current-carrying conductors in the raceway are not required to be applied when conductors are installed in a conduit or tubing nipple of _____ or less in length.

Answer: 24 inches

Section 310.15(B)(3)(a)(2) clarifies that adjustment factors for more than three (3) current-carrying conductors in raceways shall not apply where the raceway is not more than 24 inches in length. Where more than 3 current-carrying conductors are installed in short lengths of conduit or tubing, the heating effect caused from the additional conductors is insignificant therefore, the allowable ampacity of the conductors is not greatly reduced.

When lighting units, general-use receptacles, or other appliances are supplied via a branch circuit, the total marked rating of a 120-volt, cord-and-plug-connected room air conditioner shall not exceed _____ of the branch circuit's rating, according to the NEC.

Answer: 50%

According to the National Electrical Code (NEC) Article 440.62(B), when a branch circuit supplies other loads like lighting or general-use receptacles, the total marked rating of a cord-and-plug-connected room air conditioner cannot exceed 50% of the branch circuit's ampere rating. This rule ensures that there is sufficient capacity remaining on the circuit for other connected appliances and lighting, preventing overloading and potential safety hazards.

Which of the following should not be placed over a stairway step?

Answer: overcurrent devices

The National Electrical Code (NEC) Article 240.24(D) specifically prohibits locating overcurrent devices, such as circuit breaker panels or fuse boxes, over the steps of a stairway. This safety regulation is in place to prevent individuals from falling and sustaining injuries while attempting to access or work on these electrical components. Working on electrical panels requires stable footing, which a stairway step does not provide.

At least one (1) single-phase, 125-volt, 15- or 20-ampere receptacle must be located not less than _____ from and not more than _____ from the inside wall of a permanently installed outdoor swimming pool on residential or commercial properties.

Answer: 6 feet - 20 feet

The National Electrical Code (NEC) Article 680.22(A)(1) mandates the placement of at least one single-phase, 125-volt, 15- or 20-ampere receptacle near permanently installed outdoor swimming pools. This receptacle must be located not less than 6 feet and not more than 20 feet from the inside wall of the pool. This requirement ensures convenient access for pool equipment while maintaining a safe distance to minimize the risk of electrical shock.