Generator Overcurrent Protection Quiz
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Questions and Answers

According to Article 440, how should motor-compressors be protected against overload and failure to start?

  • By a separate overload relay that is responsive to motor-compressor current
  • By a thermal protector integral with the motor-compressor
  • By a fuse or inverse time circuit breaker responsive to motor current
  • All of the above (correct)

    • What is the maximum percentage at which the separate overload relay should trip for motor-compressors?

  • 140% (correct)
  • 100%
  • 125%
  • 150%

    • Which devices are permitted to serve as the branch-circuit short-circuit and ground-fault protective device for motor-compressors?

  • Separate overload relay
  • Thermal protector integral with the motor-compressor
  • Fuse or inverse time circuit breaker (correct)
  • All of the above

    • Which standard defines a stationary unit (generator) as 'an engine generator that is intended to be hard-wired and/or permanently installed'?

    <p>UL 2200</p> Signup and view all the answers

    Which type of generator must be marked with their reactances using the correct industry terms?

    <p>Portable generators</p> Signup and view all the answers

    Which article covers the installation and other requirements for generators?

    <p>Article 445</p> Signup and view all the answers

    Which standard provides information on the location of generators?

    <p>NFPA 37-2021</p> Signup and view all the answers

    According to the text, what is the purpose of compliance with 445.18(A)?

    <p>To protect the worker servicing the generator</p> Signup and view all the answers

    What is the requirement for the means of shutdown of the prime mover according to the text?

    <p>To equip provisions for backfeed protection</p> Signup and view all the answers

    According to the text, what is the purpose of disabling all prime mover start control circuits?

    <p>To protect the worker servicing the generator</p> Signup and view all the answers

    According to the text, what type of room air conditioners does Part VII apply to?

    <p>Room air conditioners that control temperature and humidity</p> Signup and view all the answers

    According to the text, how should the enclosures of room air conditioners be connected?

    <p>To the equipment grounding conductor</p> Signup and view all the answers

    According to the text, what is the maximum length of a flexible cord used to supply a room air conditioner rated 120 volts?

    <p>3.0 m (10 ft)</p> Signup and view all the answers

    According to the text, what type of protection device should single-phase cord- and plug-connected room air conditioners be provided with?

    <p>Leakage-current detector-interrupter (LCDI)</p> Signup and view all the answers

    Which type of generators are being manufactured with inverter-based designs?

    <p>All generators</p> Signup and view all the answers

    What is the minimum ampacity of the conductors from the generator output terminals to the first distribution device(s) containing overcurrent protection?

    <p>100 percent of the nameplate current rating of the generator</p> Signup and view all the answers

    What type of overcurrent protection is required for two-wire, dc generators?

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

    What is the ampacity requirement for neutral conductors of dc generators that must carry ground-fault currents?

    <p>Larger than the minimum required size of the largest conductor</p> Signup and view all the answers

    Which of the following is true about conductors supplied from the generator output terminals?

    <p>They must have a minimum ampacity based on the nameplate current rating of the generator.</p> Signup and view all the answers

    Under what conditions are tapped conductors permitted from the load side of the protected terminals of a generator set equipped with overcurrent protection?

    <p>When the generator set is equipped with a listed overcurrent protective device or a combination of a current transformer and overcurrent relay.</p> Signup and view all the answers

    For which type of generators are tapped conductors not permitted?

    <p>Portable generators rated 15 kW or less where field wiring connection terminals are not accessible.</p> Signup and view all the answers

    What provides short-circuit protection for the tap conductors in a generator equipped with a listed branch-circuit overcurrent protective device or a combination of a current transformer and overcurrent relay?

    <p>The listed branch-circuit overcurrent protective device or a combination of a current transformer and overcurrent relay on the tap conductor source side terminals.</p> Signup and view all the answers

    Which of the following devices can be used for overload protection for motor-compressors and equipment on 15- and 20-ampere, single-phase, branch circuits?

    <p>A fuse or inverse time circuit breaker</p> Signup and view all the answers

    What is the maximum continuous current that a thermal protector applied in accordance with 440.52(A)(2) should permit?

    <p>156 percent of the marked rated-load current or branch-circuit selection current</p> Signup and view all the answers

    What type of protection should be provided for motor-compressors and equipment used on 15- or 20-ampere 120-volt, or 15-ampere 208- or 240-volt, single-phase branch circuits?

    <p>Overload protection</p> Signup and view all the answers

    What is the maximum rating for the attachment plug and receptacle or cord connector for motor-compressors and equipment that are cord- and attachment-plug-connected and used on 15- or 20-ampere 120-volt, or 15-ampere 208- or 240-volt, single-phase branch circuits?

    <p>20 amperes at 125 volts or 15 amperes at 250 volts</p> Signup and view all the answers

    According to the text, what is the purpose of the emergency engine shutdown device?

    <p>To disconnect the generator from the equipment it supplies</p> Signup and view all the answers

    Which of the following is true about the engine shutdown device used as a disconnecting means?

    <p>It must be capable of being locked in the open position</p> Signup and view all the answers

    When is the engine shutdown device not required to be a locking-type device?

    <p>When it is used only as the engine shutdown required by 445.19(A)</p> Signup and view all the answers

    Which of the following is NOT a reason why an overcurrent device should not be installed in series with the shunt winding of an autotransformer between Points A and B?

    <p>Exception for autotransformers with input current less than 9 amperes</p> Signup and view all the answers

    What is the purpose of the 2-pole disconnect switch with overcurrent devices OC-1a and OC-1b in the exhibit?

    <p>To protect the input circuit</p> Signup and view all the answers

    Why is it not permitted to have an overcurrent device located in series with the shunt winding and the overcurrent device in an autotransformer?

    <p>Voltage feedback problem</p> Signup and view all the answers

    According to the text, which type of generators are required to have a remote emergency stop switch?

    <p>Generators with a rating greater than 15 kW</p> Signup and view all the answers

    What is the purpose of requiring shutdown of the prime mover for generators greater than 15 kilowatts?

    <p>To provide a remote shutdown means in the event of an emergency</p> Signup and view all the answers

    According to the text, where should the emergency shutdown device be located for one- and two-family dwelling units?

    <p>Outside the dwelling unit at a readily accessible location</p> Signup and view all the answers

    What is the requirement for ground-fault circuit-interrupter (GFCI) protection on receptacles of 15-kW or smaller portable generators?

    <p>Receptacle outlets shall have listed GFCI protection for personnel</p> Signup and view all the answers

    According to Table 450.3(A), what is the maximum rating or setting of overcurrent protection for transformers rated over 1000 volts in supervised locations only?

    <p>300%</p> Signup and view all the answers

    What is the maximum rating or setting of overcurrent protection for transformers rated over 1000 volts in any location with a secondary rated over 1000 volts and a transformer with 6% impedance?

    <p>600%</p> Signup and view all the answers

    How many circuit breakers or sets of fuses are permitted for secondary overcurrent protection in transformers rated over 1000 volts?

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

    What is the maximum percentage of the rated secondary current that the sum of the ratings of the circuit breakers for secondary protection in transformers rated over 1000 volts is permitted to exceed?

    <p>300%</p> Signup and view all the answers

    Which type of transformers are not covered by Article 450?

    <p>Transformers used with Class 2 and Class 3 circuits</p> Signup and view all the answers

    What is the purpose of the exception to 445.20(A)?

    <p>To address the problems of proper operation of a GFCI-protected 125-volt receptacle on a generator</p> Signup and view all the answers

    Which sections in Article 240 and Article 245 are referenced in the informational note?

    <p>240.4 and 245.27</p> Signup and view all the answers

    What is the purpose of compliance with Article 450?

    <p>To provide guidance for the installation of transformers</p> Signup and view all the answers

    According to Table 450.3(B), what is the maximum rating or setting of overcurrent protection for transformers with currents less than 9 amperes?

    <p>250%</p> Signup and view all the answers

    What is the maximum rating or setting of overcurrent protection for transformers with currents of 9 amperes or more, according to Table 450.3(B)?

    <p>125%</p> Signup and view all the answers

    Which method of protection requires primary protection only for transformers, according to Table 450.3(B)?

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

    Which method of protection requires secondary side overcurrent protection at not more than 125 or 167 percent, provided the primary side overcurrent protection is not more than 250 percent of the primary side current rating, according to Table 450.3(B)?

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

    Which of the following is true about the primary overcurrent device for a transformer?

    <p>It provides short-circuit protection for the transformer</p> Signup and view all the answers

    In which cases can the secondary circuit conductors of a transformer be protected by overcurrent devices in the primary circuit conductors?

    <p>For a transformer with a 2-wire primary and a 2-wire secondary</p> Signup and view all the answers

    What methods can be used to handle the increased heating effects of nonlinear load currents on a transformer?

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

    For applications rated not more than 1000 volts, nominal, what article covers the overcurrent protection requirements for transformer conductors?

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

    Which of the following is the correct equation to calculate the voltage that would appear across the primary winding of a transformer when the load impedance is very low?

    <p>$208/32 × 208$</p> Signup and view all the answers

    What is the voltage that would appear across the primary winding of a transformer when the load impedance is very low and the supply voltage is 208 volts?

    <p>$208/32 × 208$</p> Signup and view all the answers

    What is the voltage that would appear across the primary winding of a transformer when the load impedance is very low and the supply voltage is 240 volts?

    <p>$240/32 × 240$</p> Signup and view all the answers

    According to 450.14, where should the disconnecting means for transformers (other than Class 2 or Class 3 transformers) be located?

    <p>Either in sight of the transformer or in a remote location</p> Signup and view all the answers

    According to 450.21(A), what are the separation requirements for transformers from combustible materials?

    <p>10 feet</p> Signup and view all the answers

    According to 300.22(C)(3), in what type of spaces are transformers permitted to be installed?

    <p>Hollow spaces used for environmental air</p> Signup and view all the answers

    Which type of protective device must be provided on the secondary side of the network transformers?

    <p>Circuit breaker and reverse-current relay</p> Signup and view all the answers

    What is the purpose of the reverse-current relay in the network protector?

    <p>To prevent power from being fed back into the transformer</p> Signup and view all the answers

    What type of protective device is commonly used to protect the secondary ties in the network system?

    <p>Current limiter</p> Signup and view all the answers

    What is the grounding requirement for the transformer secondary supplying the grounded secondary tie system?

    <p>Grounded in accordance with 250.30 for separately derived systems</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of overcurrent protection for transformers rated over 1000 volts in any location with a secondary rated over 1000 volts and a transformer with 6% impedance?

    <p>167 percent of the primary side current rating</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of overcurrent protection for transformers rated over 1000 volts in supervised locations only?

    <p>250 percent of the primary side current rating</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of overcurrent protection for transformers with currents less than 9 amperes?

    <p>42 percent of the primary side current rating</p> Signup and view all the answers

    According to the text, what is the maximum percentage of the rated secondary current that the sum of the ratings of the circuit breakers for secondary protection in transformers rated over 1000 volts is permitted to exceed?

    <p>150 percent</p> Signup and view all the answers

    Which of the following is true about the installation of grounding autotransformers on the load side of a supply system grounding connection?

    <p>It is prohibited for services, separately derived systems, and feeders and branch circuits that supply separate buildings or structures.</p> Signup and view all the answers

    What type of transformer is used to create a neutral reference point on a circuit supplied from a grounded system?

    <p>Zigzag transformer</p> Signup and view all the answers

    In what scenario can a line-to-ground fault in a feeder circuit cause serious damage to a zigzag transformer?

    <p>When the rating of the circuit in which the line-to-ground fault occurs exceeds the rating of the circuit in which the zigzag transformer is used.</p> Signup and view all the answers

    What type of autotransformer is used to create a 3-phase, 4-wire distribution system from a 3-phase, 3-wire ungrounded system?

    <p>Grounding autotransformer</p> Signup and view all the answers

    According to the text, what is the purpose of compliance with IEEE C57.12.00-2015 and IEEE C57.12.01-2020?

    <p>To dispose of transformer full-load heat losses without exceeding the transformer rating</p> Signup and view all the answers

    According to the text, what is the purpose of marking the required clearances on the transformer?

    <p>To prohibit storage on the horizontal and readily accessible top surfaces of the transformer</p> Signup and view all the answers

    According to the text, what is the purpose of bonding the terminal bar to the enclosure in a dry-type transformer?

    <p>To prevent the transformer enclosure from being evaluated as a grounding and bonding device</p> Signup and view all the answers

    According to the text, when are dry-type transformers 1000 volts or less located in the open not required to be readily accessible?

    <p>When they meet the ventilation requirements</p> Signup and view all the answers

    According to Article 450, what is the ampacity requirement for the tie circuit if loads are connected at the transformer supply points at each end of the tie and overcurrent protection is not provided in accordance with Parts I, II, and VIII of Article 240?

    <p>67 percent of the rated secondary current of the highest rated transformer supplying the secondary tie system</p> Signup and view all the answers

    What is the ampacity requirement for the tie circuit if load is connected to the tie at any point between transformer supply points and overcurrent protection is not provided in accordance with Parts I, II, and VIII of Article 240?

    <p>100 percent of the rated secondary current of the highest rated transformer supplying the secondary tie system</p> Signup and view all the answers

    Under what conditions should the conductors of each phase or neutral comply with 450.6(A)(4)(a) or (A)(4)(b)?

    <p>When the tie consists of more than one conductor per phase or neutral</p> Signup and view all the answers

    What is the requirement for the means of interconnection for the conductors of each phase or neutral in a tie circuit that is not interconnected?

    <p>The loads shall be connected to one or more individual conductors of a paralleled conductor tie without interconnecting the conductors of each phase or neutral</p> Signup and view all the answers

    According to the text, what is the minimum separation required for dry-type transformers rated 1121⁄2 kVA or less from combustible material when installed indoors?

    <p>300 mm (12 in.)</p> Signup and view all the answers

    According to the text, what is the minimum fire rating required for the transformer room for individual dry-type transformers rated over 1121⁄2 kVA?

    <p>1-hour fire rating</p> Signup and view all the answers

    According to the text, which type of transformers are exempted from the requirement of being installed in a transformer room?

    <p>Transformers with Class 155 or higher insulation systems and completely enclosed except for ventilating openings</p> Signup and view all the answers

    According to the text, what is the minimum insulation system rating required for dry-type transformers to be exempt from installation in transformer rooms or vaults?

    <p>Class 155</p> Signup and view all the answers

    According to the text, what is the maximum primary voltage allowed for dry-type transformers to be commonly used indoors?

    <p>35,000 volts</p> Signup and view all the answers

    According to the text, what is the minimum separation required for dry-type transformers rated 112½ kilovolt-amperes or less from combustible material?

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

    According to the text, what is the maximum distance allowed between dry-type transformers exceeding 112½ kVA and combustible materials of buildings, if the transformers have Class 155 insulation systems or higher and are completely enclosed except for ventilating openings?

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

    Which type of transformers have the greatest need for passive protection to prevent the spread of burning oil to other combustible materials?

    <p>Transformers insulated with mineral oil</p> Signup and view all the answers

    What is the minimum fire resistance requirement for the walls and roofs of transformer vaults?

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

    What is the minimum thickness requirement for the concrete floors of transformer vaults in contact with the earth?

    <p>100 mm (4 in.)</p> Signup and view all the answers

    What is the minimum height requirement for the door sill or curb of a transformer vault?

    <p>100 mm (4 in.)</p> Signup and view all the answers

    According to the text, what is the maximum number of parts per million PCBs that classifies a transformer as a PCB transformer?

    <p>500</p> Signup and view all the answers

    According to the text, what is the maximum total capacity of oil-insulated transformers that are permitted to be installed in a vault constructed of reinforced concrete?

    <p>1121/2 kVA</p> Signup and view all the answers

    According to the text, what is the maximum total rating of electric furnace transformers that are permitted to be installed without a vault in a building or room of fire-resistant construction?

    <p>75 kVA</p> Signup and view all the answers

    According to the text, what is the maximum total rating of a transformer that is permitted to be installed without a vault in a building or room of noncombustible or fire-resistant construction, if it is an integral part of charged-particle-accelerating equipment?

    <p>75 kVA</p> Signup and view all the answers

    Which of the following information is required to be indicated on the nameplate of each phase converter according to the text?

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

    What is the purpose of sizing single-phase conductors to prevent a voltage drop not exceeding 3 percent from the source of supply to the phase converter according to the text?

    <p>To ensure proper starting and operation of motor loads</p> Signup and view all the answers

    According to the text, what is the ampacity requirement for the single-phase supply conductors of a phase converter?

    <p>It depends on the rated input and output voltages</p> Signup and view all the answers

    Which type of phase converter does not have any moving parts?

    <p>Static-phase converter</p> Signup and view all the answers

    What is the minimum net area required for ventilation openings in a vault ventilated by natural circulation of air?

    <p>0.1 m2 (1 ft2)</p> Signup and view all the answers

    What is the maximum rating or setting of overcurrent protection for transformers rated over 1000 volts in any location with a secondary rated over 1000 volts and a transformer with 6% impedance?

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

    What is the purpose of installing a drain or other means for carrying off oil or water accumulation in vaults containing more than 100 kVA transformer capacity?

    <p>To facilitate maintenance</p> Signup and view all the answers

    According to the text, what is the purpose of a liquid confinement area in a nonflammable-fluid-insulated transformer?

    <p>To limit the extent of a spill if the tank leaks or ruptures</p> Signup and view all the answers

    According to 450.24, what is the requirement for nonflammable-fluid-insulated transformers installed indoors and rated over 35,000 volts?

    <p>They must be installed in a vault</p> Signup and view all the answers

    What is the purpose of a pressure-relief vent in a nonflammable-fluid-insulated transformer?

    <p>To provide pressure relief in case of a leak or rupture</p> Signup and view all the answers

    According to the text, why is a means for absorbing gases generated by arcing necessary in a nonflammable-fluid-insulated transformer?

    <p>To prevent the formation and emission of toxic or corrosive compounds</p> Signup and view all the answers

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