The edge: Things you should know

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  1. individual conductors shall be insulated or covered. What is the exception? Considering a grounded conductor.
    The grounded conductor of a multi conductor cable shall be permitted to be bare. NEC 230.22 exc.
  2. the difference between a neutral and a grounded circuit conductor is?
    A. only a neutral will have equal potential to the ungrounded conductors
    B. only a neutral outer covering his white or natural gray 
    C. only a neutral carries unbalanced current
    D. there is no difference
    • A. only a neutral will have equal potential to the ungrounded conductors
    • B. only a neutral outer covering his white or natural gray
    • C. only a neutral carries unbalanced current
    • D. there is no difference
    • in the NEC handbook under Article 200. 1 it states "the grounded conductor is often, but not always, the neutral conductor. As defined in Article 100, a neutral conductor is one that is connected to the neutral point of an electrical system. In a single phase, 2 wire or 3 phase, corner grounded Delta system, the intentionally grounded conductor is not a neutral conductor, because it is not connected to a system nuetral point. 
  3. power factor is ______ _________ of current and voltage in an AC circuit?
    phase displacement. Source: Journeyman Electrician exam questions and answers, Tom Henry 2011. Also it is the formula/ratio of TP/AP (true power to apparent power and R/Z (Resistance to impedance.  The angle theta in a voltage or impedance triangle as well.
  4. hysteresis is? 
    A. the tool used to read the specific gravity of a battery  
    B the lagging of magnetism, in a magnetic metal, behind the magnetizing flux which produces it.
    C. The opposite of impedance
    D. none of these
    • A. the tool used to read the specific gravity of a battery  
    • B the lagging of magnetism, in a magnetic metal, behind the magnetizing flux which produces it.
    • C. The opposite of impedance 
    • D. none of these
  5. PVC shall have a minimum burial depth of?
    18 inches. source: table NEC 300.5, for 1KV to 22KV, above which the burial depth increases 6 inches.
  6. is enamel painted conduit allowed to be used outdoors?
    • No.
    • Source: n.e.c 306.1
  7. the Wheatstone bridge method is used for accurate measurements of?
    • Resistance
    •  A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Its operation is similar to the original potentiometer. It was invented bySamuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. One of the Wheatstone bridge's initial uses was for the purpose of soils analysis and comparison.
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  8. which of the following is true?
    A. EMT may be threaded
    B. the white colored conductor connected to the silver colored post on a duplex receptacle on a 120 volt two wire branch circuit is called the neutral conductor
    C. plastic water pipe is approved to be used for electrical conduit
    D. the screw shell of a lampholder may support a fixture Weighing 6 pounds.
    D. Per NEC 314.27A1 exc. a vertically mounted luminaire or lampholder weighing not more than 6 pounds shall be permitted to be supported on other boxes or plaster rings that are secure to other boxes, provided that the lumineer or its supporting yoke, or the lamp holder, is secured to the box with no less than two number 6 or larger screws.
  9. when a circuit breaker is in the open position do you have a short in the grounded or the ungrounded conductor?
    either. However, if the question poses an ungrounded Delta system then it would not include the neutral and this is how Europe does things.  The Wye system is rarely common. Remember also a neutral carries unbalanced load and a grounded conductor does not. Tom Henry’s 2011 Journeyman Electrician exam questions and answers pp 21
  10. wire connectors are generally classified as what type? Thermal or pressure?
    both.
  11. voltage of a circuit is best defined as?
    the effective difference of potential between two conductors.  Also represented by .707(Peak voltage)
  12. When calculating a single motor’s wire size you find the FLC (full load current) wire size in the ampacity tables 310.15(B)2(6) in 2015, is this the wire size? 

    At what voltage does part 2 of art 430 apply?
    No.  An adjustment factor of 125 percent must be applied for a continuous DUTY motor. NEC 430.22 or art 430 part 2.

    part 2 (motor circuit conductors) of art 430 shall not apply to motor circuits over 1000 NOMINAL volts. (Nor does part 3: Motor and branch circuit overload protection)

    please note that in the 2017 handbook it states in the informational section part 3 art. 430(A)1 that a continuous duty motor is not the same as a continuous load. As defined in art 100 by the term duty.
  13. what is the difference between the terms continuous duty and continuous load in NEC art 100 definitions?
    Continuous duty and continuous load are not the same.  Duty refers to operation at a substantially constant load for an indefinitely long time. Whereas, load is for maximum current for 3 hours or more.
  14. What is the current drawn when PF is .91? This question requires what mathematical formula?
    • watts         
    • pf x voltage
  15. What must be remembered when using the lighting load demand factors, table 220.42 when calculating the total number of branch circuits for illumination?
    That table 220.42 “lighting load demand factors” shall not be used in determining the number of branch circuits.
  16. The amperage in a dual voltage motor will be ______ if the voltage is doubled despite ohm’s law finding I using R.

    Example question: A dual-voltage three-phase motor draws a current of 45 amperes when connected to a 240 volt, three phase circuit.  How much current will the same motor draw if connected to a 480 volt three-phase circuit? Source: Electrician’s exam preparation guide, Dale C. Brickner, 2011: PP 48
    halfed.  Remember that a dual voltage motor will have the winding in series for high voltage and parallel for low voltage.
  17. What formula is used to find ‘R’ (resistance) in a length of wire? You will need to know the specific resistance for copper and aluminum.  What are they?
    • R=K×L
    •      CM  ;where CM is circular mils, K is specific resistance of 12.9 for copper and 21.2 for Aluminum, and L is length. Notice the 2kli/cm would be a voltage drop calculation for single phase.
  18. Motor branch circuits and feeders ocpd is rounded up or down?
    • Motor branch circuits are rounded up and feeders are rounded down.  
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  19. What is the Cubic inches of a #14 awg wire and a #12 wire?
    • #12 is 2.25 cu in.
    • #14 is 2.00 cu in.
  20. What is a motor branch circuit? Define.
    Would the below image showing a conductor supplying multiple motors be a branch circuit?
    • That portion of the circuit that extends beyond the final over current protection. No. NEC definitions
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  21. Noninsulated busbars will have a minimum space of_______ inches between the bottom of enclosure and busbars. What about insulated busbars?
    10 inches is the maximum space between enclosures and this. NEC T408.5 And 8 inches if insulated.
  22. Although a wound rotor motor is used for speed control applications, what type of motor has a large speed range?
    A DC motor has this. Tom Henry 2011 Journeyman Exam Questions and Answers. PP4
  23. The normal rotation of an induction motor is? facing the front of the motor. (The front of motor is the end opposite the shaft).
    Counterclockwise is the normal rotation for this type of motor, not facing the shaft; whereas it is clockwise facing the shaft. Tom Henry 2011 Journeyman Exam Questions and Answers. PP19

    It's based on the direction of the rotating magnetic field, which is dependant on the phase rotation. Hence if you swap in two line leads on a three phase motor, the direction of the magnetic field and thus motor will reverse. (This would usually be T1 and T3)

    Reference https://www.physicsforums.com/threads/3-phase-induction-motor-direction-of-rotation.229734/
  24. What electrical apparatus concerns a Class A device?
    Ground-Fault Circuit Interrupter (GfCl)- A device intended for the protection of personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a class A device.  NEC Definitions article 100.
  25. open circuit test on a transformer is a test for measuring what?  Define this.
    • iron losses are tested with this test on a transformer keeping the HV side open and using the LV side. iron loss: the loss of available energy by hysteresis and eddy currents in an electromagnetic apparatus (as a transformer) versus copper loss. Tom Henry 2011 Journeyman Exam Questions and Answers. PP30
    • Usually high voltage (HV) winding is kept open and the low voltage (LV) winding is connected to its normal supply. A wattmeter (W), ammeter (A) and voltmeter (V) are connected to the LV winding as shown in the figure. Now, applied voltage is slowly increased from zero to normal rated value of the LV side with the help of a variac. When the applied voltage reaches to the rated value of the LV winding, readings from all the three instruments are taken.
  26. hot resistance of an incandescent lamp is approximately______times its cold resistance.
    This type of resistance in an incandescent lamp is ten times the cold resistance. Tom Henry 2011 Journeyman Exam Questions and Answers. PP34
  27. What is the below image a picture of?Image Upload
    Amphenol Plugs.  They must have the wires soldered on one end
  28. When are you allowed to support an enclosure that does not contain a device(s), other than splicing devices, or supports a luminaire(s), a lampholder, or other equipment and is supported by entering raceways only…..?
    • ….shall not exceed 1650 cm3 or 100 in 3 in size. It shall have threaded entries or identified hubs. It shall 1 be supported by two or more conduits threaded wrench tight into the enclosure hubs. Each conduit shall be secured within 900 ram (3 ft) the enclosure, or within 450 mm (18 in.) of the enclosure if all conduit entries are on the same side. 
    • Source: 314.23E 2017 NEC
  29. Non-combustible surfaces that are broken or incomplete around boxes employing a flush-type cover or faceplate shall be repaired so there will be no gaps or open spaces greater than?
    • 3 mm (1/8 in.) at the edge of the box.
    • Source: 314.21 NEC 2017
  30. Is it allowable to have conductors of each phase, ground, or EGC to be grouped together in parallel conduits by isolated phase?  A phase in one, B in another, and so on?  Site the code section if it is allowed.
    • NEC 300.3B1
    • Exception: Conductors installed in nonmetallic raceways and run underground shall be permitted to be arranged as isolated phase, neutral, and grounded conductor installations. The race shall be installed in close proximity, and the isolated phase, neutral, and grounded conductors) shall comply with the provisions of 300.20(B)
  31. What is another term for an ATS the is an open transitions transfer switch?
    open transition transfer switch is also called a break-before-make transfer switch. A break-before-make transfer switch breaks contact with one source of power before it makes contact with another. It prevents backfeeding from an emergency generator back into the utility line, for example
  32. What is another name for a closed automatic transfer switch?
    A closed transition transfer switch (CTTS) is also called a make-before-break transfer switch.

    A typical emergency system uses open transition, so there is an inherent momentary interruption of power to the load when it is transferred from one available source to another (keeping in mind that the transfer may be occurring for reasons other than a total loss of power). In most cases this outage is inconsequential, particularly if it is less than 1/6 of a second.  these require a less than 100 millisecond transfer.
  33. Why is single point grounding so necessary? Consider lightning.
    The reference paragraph below explains that between any two points on a conductor, or lets say ground system, you may have significant potential differences as current resulting from lighting activity is introduced into this conductor or the conductors of the system. With DC current we merely consider the true circuit resistance. With AC and RF we must consider the impedance of the circuit and that is where the 600 kV of the example below comes into play.

    • By having all equipment, including antenna transmission lines, power, telephone, cable TV, etc, all entering the facility at nearly the same point and all being bonded to a single common ground point, little current will flow between these systems and therefore there will be essentially no difference of potential between the components of the system (everything within the shelter) during lightning activity.  
    • -mike holt
    • http://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/Single-Point-Ground~20040427.php
  34. Consider RF transmission line theory. A quarter wave length or odd multiple of a quarter wavelength of transmission line at its resonate frequency will appear as what?
    Consider RF transmission line theory. A quarter wave length or odd multiple of a quarter wavelength of transmission line at its resonate frequency will appear "open" at the source end even if the opposite (load) end of the transmission line is effectively "short" circuited. 

    • Http://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/Single-Point-Ground~20040427.phpd segment of the spectrum
    • -mike holt
  35. According to this section, if the grounding electrode conductor is connected to a single ground rod or multiple ground rods, the grounding electrode conductor is not required to be bigger than No._____copper or No. ___aluminum. Likewise, any connection to one or more concrete-encased electrodes, such as ½ in. rebar, does not need to be larger than No. 4 copper.
    According to this section, if the grounding electrode conductor is connected to a single ground rod or multiple ground rods, the grounding electrode conductor is not required to be bigger than No. 6 copper or No. 4 aluminum. Likewise, any connection to one or more concrete-encased electrodes, such as ½ in. rebar, does not need to be larger than No. 4 copper.

    The reason for these limits is that the purpose of the grounding electrode conductor is not to carry fault current. The job of the grounding electrode conductor is to connect the non-current carrying parts of the electrical system to the earth and keep the potential on enclosures and conduit to 0 volts
  36. Is the the purpose of the GEC to conduct fault current?
    source: https://www.jadelearning.com/jadecc/courses/UNIVERSAL/NEC05.php?imDif=10109.1
    no.  The reason for these 6awg cu to a single ground rod and 4awg encased (both max) is that the purpose of the grounding electrode conductor is not to carry fault current. The job of the grounding electrode conductor is to connect the non-current carrying parts of the electrical system to the earth and keep the potential on enclosures and conduit to 0 volts. It also serves to conduct lightning strikes.
  37. Where can a system bonding jumper be landed and cite the code section.
    As noted in 250.30(A) of the NEC, a system bonding jumper must be installed at the same location where the grounding electrode conductor terminates to the neutral terminal of the separately derived system; either at the separately derived system or the system disconnecting means, but not at both locations [250.30(A)(1)].
  38. Define a bonding jumper, system. And in what code cycle was this new?
    The term Bonding Jumper, System has been added to Article 100 in the 2011 NEC and is defined as follows: The connection between the grounded circuit conductor and the supply-side bonding jumper, or the equipment grounding conductor, or both, at a separately derived system.
  39. If you are asked “what’s the apparent power in VA of two 40W lamps with a power factor of 89%.....what is the formula?
    • If you know how many watts and the PF you can find the apparent power. The formula is Watts/PF=VA
    • PP 81 “Electrical Exam Preperation” Mike Holt 2014
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johnbowens
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Card Set:
The edge: Things you should know
Updated:
2018-02-14 02:06:47
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General nec nfpa 70 code trivia. Giving the electrician an upper edge. Focusing on little known exceptions or obscure code.
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