C -10 COMMERCIAL/INDUSTRIAL
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Questions and Answers

What is the minimum recommended transformer rating to properly operate a 2HP (horsepower) 3-phase motor at 230 volts?

  • 1 kVA
  • 2 kVA
  • 3 kVA (correct)
  • 4 kVA

    • What is the standard power factor commonly considered for the 3-phase generators used in large commercial environments?

  • 0.6
  • 0.7
  • 0.8 (correct)
  • 0.9

    • What is the recommended welding process for use in underground circuit connections?

  • Exothermic (correct)
  • Endothermic
  • Retrothermic
  • Biothermic

    • What is the standard height of grounding rods commonly available in the market?

    <p>8 ft. to 10 ft.</p> Signup and view all the answers

    Which of the following service points must be directly connected to a grounding electrode?

    <p>All of the above</p> Signup and view all the answers

    Which of the following materials are commonly used in the construction of grounding rods?

    <p>Copper, Copper-Clad Steel, Stainless Steel</p> Signup and view all the answers

    Which one of the following operations is NOT associated with the functions of an electrical transformer?

    <p>Improves power factor</p> Signup and view all the answers

    What is the most common voltage on the commercial 3-phase generator sets normally used in the industry?

    <p>480 Volts</p> Signup and view all the answers

    Which of the following are the major types of equipment grounding schemes?

    <p>Clean, Dirty, Structural</p> Signup and view all the answers

    Which of the following statements is false regarding a grounding connection?

    <p>Always paint first and then install the connection</p> Signup and view all the answers

    Which of the following ratios of power de-rating will occur, if you convert a 3-phase generator to a single-phase generator through a phase conversion mechanism?

    <p>30%</p> Signup and view all the answers

    How many types of excitation are commonly used in generators?

    <p>2 Types</p> Signup and view all the answers

    Which of the following arrangements is commonly used for the improvement/correction of the power factor of an electric motor?

    <p>A parallel capacitive load</p> Signup and view all the answers

    Which of the following are two major types of 3-phase transformer connections commonly used in the industry?

    <p>Wye &amp; Delta</p> Signup and view all the answers

    Normally, what is the ratio of starting current for a 3-phase motor?

    <p>400%–1000% of full load current</p> Signup and view all the answers

    Which of the following types of induction occurs in the secondary winding of a transformer due to a revolving magnetic field in the primary winding?

    <p>Mutual induction</p> Signup and view all the answers

    Which of the following conductors should be neither switched nor fused in an electrical power system?

    <p>Neutral conductor</p> Signup and view all the answers

    Which of the following statements is NOT true about a neutral point in an alternating current electrical system?

    <p>The common point of a 3-phase/3-wire delta connection</p> Signup and view all the answers

    Which of the following factors is related to the over-excitation problem commonly observed in generators?

    <p>All of the above</p> Signup and view all the answers

    What is the phase difference between the three windings of a 3-phase induction motor?

    <p>120 electric degrees</p> Signup and view all the answers

    What is the function of a diode bridge installed on an electrical generator?

    <p>Conversion of AC power</p> Signup and view all the answers

    What are two main types of encoders commonly used on commercial motors for motion control?

    <p>Linear &amp; Rotary</p> Signup and view all the answers

    Which of the following arrangements do NEC standards warrant for a transformer that has only primary overcurrent protection?

    <p>Proper bonding and grounding of transformer</p> Signup and view all the answers

    Which of the following pairs of color codes is recommended by the NEC for neutral conductors?

    <p>Gray &amp; White</p> Signup and view all the answers

    Which of the following types of motors will require an additional starting mechanism?

    <p>Synchronous motor</p> Signup and view all the answers

    Which of the following pole numbers are commonly used in synchronous motors in the industry?

    <p>2, 4, 6</p> Signup and view all the answers

    What is the minimum gauge required for copper bonding conductors used in a system with a maximum overcurrent protection of 100 Amperes?

    <p>8 AWG</p> Signup and view all the answers

    Which of the following statements is true about an electric motor?

    <p>It converts electrical energy to mechanical energy</p> Signup and view all the answers

    If the increase in voltage output of a generator is held constant through auto voltage regulator settings while changing the frequency from 50 Hz to 60 Hz, what will be the impact on output power?

    <p>It will increase by 5%</p> Signup and view all the answers

    The center tap of the secondary winding of a split-phase transformer is connected to:

    <p>Grounded neutral</p> Signup and view all the answers

    What is the recommended size of aluminum grounding conductor required for electrical equipment, which is installed with 600-ampere overcurrent protection?

    <p>2/0 AWG</p> Signup and view all the answers

    What is the maximum allowable ratio of conduit fill for an existing conduit?

    <p>40%</p> Signup and view all the answers

    What is the range of energy loss in different types of electrical transformers?

    <p>2% to 5%</p> Signup and view all the answers

    Which of the following voltages is carried by smaller legs of commercial transformers in the electric industry?

    <p>120 volts</p> Signup and view all the answers

    Which of the following activities is not related to routine maintenance of a standby diesel generator?

    <p>No-load testing</p> Signup and view all the answers

    Which of the following voltages is carried by the wild leg of a commercial transformer?

    <p>208 volts</p> Signup and view all the answers

    Which of the following applications does NOT use an induction motor?

    <p>Paper mill</p> Signup and view all the answers

    According to NEC's definition, which of the following statements is false regarding a tap conductor?

    <p>It is a service conductor</p> Signup and view all the answers

    What minimum gauge of wire is recommended for connecting a 2 HP 3-phase motor (230/460 volts) located 100 feet away from the transformer?

    <p>12 AWG</p> Signup and view all the answers

    What is the minimum recommended width of the copper grounding strip for equipment grounding?

    <p>3.5”</p> Signup and view all the answers

    Which of the following line-to-line (phase-to-phase) voltage ratios is correct for Y-connected three-phase transformers?

    <p>1.73 times of a line-to-neutral voltage</p> Signup and view all the answers

    Which of the following conditions is required for concrete encasement when using PVC conduit for wiring electric equipment in Class I hazardous locations?

    <p>At least 2” concrete thickness &amp; 24” cover from the grade to conduit top</p> Signup and view all the answers

    Electrical motors can be found in all of the following applications except:

    <p>Expressway</p> Signup and view all the answers

    Which of the following problems will occur, if the prime mover of any one of the two generators operating in parallel/synch fails?

    <p>Reversal of power will occur in the faulty generator</p> Signup and view all the answers

    What is the maximum resistance of a single rod, plate, or pipe used as a grounding electrode?

    <p>25 Ohms</p> Signup and view all the answers

    Which of the following types of wires is commonly used to handle 110–600 volts in wet as well as dry conditions?

    <p>All of the above</p> Signup and view all the answers

    According to the NEC, a transformer containing liquid that can burn is required to be installed _____________ in Class I/Division I locations.

    <p>In a closed vault</p> Signup and view all the answers

    What is the minimum recommended size of spare conduit while laying cable conduits from a transformer to power distribution system panels?

    <p>2”</p> Signup and view all the answers

    Which of the following is NOT a part of a 3-phase induction motor?

    <p>Slip ring</p> Signup and view all the answers

    What is the minimum recommended distance between two rods, plates, or pipes when using a two-rod grounding electrode?

    <p>6 feet</p> Signup and view all the answers

    Which of the following parameters is tested and verified through Megger testing on electrical transformers?

    <p>Insulation Resistance</p> Signup and view all the answers

    If the primary windings are a higher voltage and the secondary windings are a lower voltage, what type of transformer is this?

    <p>Step down transformer</p> Signup and view all the answers

    What is the phase-to-phase (line-to-line) voltage of a commonly used split-phase transformer?

    <p>240 volts</p> Signup and view all the answers

    What will happen if the frequency of a 50 Hz generator is changed to 60 Hz?

    <p>Nominal voltage increases by 20%</p> Signup and view all the answers

    Which of the following tap conductor rules, as recommended by the NEC, commonly applies in commercial electrical services?

    <p>25-foot tap rule</p> Signup and view all the answers

    Which one of the following transformer tests is very critical for connecting multiple transformers in parallel or in a bank?

    <p>Polarity test</p> Signup and view all the answers

    What is the minimum gauge of copper ground ring required for a grounding electrode?

    <p>2 AWG</p> Signup and view all the answers

    Which of the following may be the result of a faulty voltage regulator on a 3-phase generator?

    <p>All of the above</p> Signup and view all the answers

    Which of the following materials is used to manufacture the core of an electric transformer?

    <p>Thin sheets of silicon and steel alloy</p> Signup and view all the answers

    According to NEC standards, what is the maximum allowable percentage of overload protection on each phase of a motor marked with a temperature rise up to 104°F?

    <p>125% of full load current</p> Signup and view all the answers

    Which of the following tests is NOT performed on an oil sample taken from a transformer?

    <p>Voltage drop</p> Signup and view all the answers

    Which of the following positions is the correct connecting point for a neutral conductor in a Star (Wye) connection of a transformer?

    <p>Center of Wye connection</p> Signup and view all the answers

    Which of the following arrangements is commonly used to step-up and step-down the voltage in a transformer?

    <p>Winding turn ratio</p> Signup and view all the answers

    What is the minimum melting point of a sealing compound required for sealing the cable conduits used for electrical equipment installation in Class I/Division 1 locations?

    <p>200°F</p> Signup and view all the answers

    What problem can occur if proper lubrication of a motor is not done on a recommended time interval?

    <p>Bearings will cease to move</p> Signup and view all the answers

    According to NEC standards, which of the following surge protection arrangements is mandatory on commercial electrical installations in Class I/Division 1 locations?

    <p>All of the above</p> Signup and view all the answers

    Which of the following statements is NOT true about the grounding of a transformer-driven alternating current system?

    <p>Any size of grounding electrode can be used</p> Signup and view all the answers

    What is the recommended size of grounding copper conductor required for electrical equipment that is installed with a 600-ampere overcurrent protection?

    <p>1 AWG</p> Signup and view all the answers

    Which heat removal mechanism is commonly used in large commercial transformers?

    <p>Oil cooling</p> Signup and view all the answers

    According to the NEC, which of the following points can be used for the grounding of a transformer-driven alternating current system?

    <p>All of the above</p> Signup and view all the answers

    How long do the motor starting capacitors normally operate in the motor-starting circuit to start a motor?

    <p>3 to 5 seconds</p> Signup and view all the answers

    Which type of generator is commonly used for the generation of high power in commercial electrical systems?

    <p>Rotating field synchronous generators</p> Signup and view all the answers

    Which of the following devices disconnects the starting windings on an induction motor when it reaches 80% of its speed?

    <p>Centrifugal switch</p> Signup and view all the answers

    Which of the following can be the possible cause of a generator running at no load but with no AC output?

    <p>All of the above</p> Signup and view all the answers

    In a 3-phase generator, which of the following feeds voltage to an auto voltage regulator (AVR)?

    <p>Auxiliary windings</p> Signup and view all the answers

    Which of the following color codes is specified for a grounding conductor?

    <p>Green</p> Signup and view all the answers

    If a generator is running on no load and AC output voltage remains between 60 V to 100 V, which of the following may be the cause of the problem?

    <p>Voltage regulator may be faulty</p> Signup and view all the answers

    Which of the following is the main reason of development of overcurrent in electric motors?

    <p>All of the above</p> Signup and view all the answers

    The measurement of continuous overload capacity at which a motor can operate without any damage to its life/performance is known as:

    <p>Service factor</p> Signup and view all the answers

    Which of the following types of transformers is commonly used?

    <p>All of the above</p> Signup and view all the answers

    If the load on a squirrel cage induction motor is reduced from the rated load, what will be the impact on the power factor?

    <p>Power factor decreases</p> Signup and view all the answers

    What is the maximum allowable phase unbalance for the proper operation of electrical motors?

    <p>1%</p> Signup and view all the answers

    What is the recommended conduit size for a luminary pole to junction box with a distance between about 5 ft. to 10 ft?

    <p>1”</p> Signup and view all the answers

    Which of the following factors directly affect the speed of a synchronous motor?

    <p>Frequency</p> Signup and view all the answers

    How many classes of hazardous locations have been identified by the NEC recommendations for commercial electrical equipment installation?

    <p>3 Classes</p> Signup and view all the answers

    What is the impact on the lubrication interval of a motor that is installed vertically?

    <p>Lubrication interval halves</p> Signup and view all the answers

    Which of the following is the industry's best practice for the installation of a conduit while crossing a roadway?

    <p>Installation of one extra conduit</p> Signup and view all the answers

    Which of the following equipment is commonly used to check the health of diodes in the bridge connection installed on generators?

    <p>Ohmmeter</p> Signup and view all the answers

    Which of the following pairs of insulation colors is NOT recommended by the NEC for phase (Hot) conductors?

    <p>White &amp; Green</p> Signup and view all the answers

    Which of the following protection systems is commonly used for controlling the voltage of a generator?

    <p>Automatic voltage regulator (AVR)</p> Signup and view all the answers

    Which of the following motors is NOT a synchronous motor?

    <p>Squirrel cage motor</p> Signup and view all the answers

    What is the maximum allowable voltage of any electrical part that can be left without insulation in dry conditions for Class I/Division 1 locations?

    <p>30 Volts</p> Signup and view all the answers

    If a motor uses a cord and plug as a disconnect, what should the attachment plug be rated for?

    <p>Horsepower</p> Signup and view all the answers

    How much electric power, in watts, will a 1-horsepower (HP) motor consume while operating at ideally 100% efficiency?

    <p>746 watts</p> Signup and view all the answers

    Which of the following motors produces constant speed?

    <p>Synchronous motor</p> Signup and view all the answers

    What is the maximum tolerable variation in power frequency that a commercial motor can withstand for proper motor operation?

    <p>5%</p> Signup and view all the answers

    How many divisions of each class of hazardous location have been identified by NEC standards?

    <p>2 Divisions</p> Signup and view all the answers

    Which of the following are two major types of alternating current motors extensively used in the industry?

    <p>Induction motor &amp; Synchronous motor</p> Signup and view all the answers

    What is the standard tolerable variation of voltage for 3-phase motors commonly used in the industry?

    <p>+/- 10%</p> Signup and view all the answers

    Which of the following problems for 3-phase generators is the main reason for negative phase sequence in the generators?

    <p>Unbalanced phase currents</p> Signup and view all the answers

    Which of the following types of motor requires an additional DC power source other than an alternating current source?

    <p>Synchronous motor</p> Signup and view all the answers

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