Unit 5: Box and Raceway Sizing Flashcards
Applying NEC® requirements to properly size outlet, junction, and pull boxes, as well as raceways, ensuring adequate space for conductors, fittings, and code compliance.
Fill in the blank:
Where flexible cord is used as the wiring method to supply ac motors, the MINIMUM size of the conductors shall be selected in accordance with ________ of the NEC®.
Section 400.5
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When an industrial control panel is supplied from a 3-phase, 4-wire, delta-connected electrical system, the phase having the higher voltage to ground is ________.
required to be the “B” phase
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When used outdoors and ambient temperature is not a factor, size 6/3 w/g Type UF cable has an ampacity of ________.
55 amperes
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Shore power for boats shall be provided by single “twist-lock” receptacles rated NOT less than ________.
30 amperes
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Where a mobile home has the main service disconnecting means installed outdoors, the disconnecting means shall be installed so the bottom of the enclosure is NOT less than ________ above finished grade.
Two feet
Determine the ampacity of a 3-conductor size 6 AWG XHHW aluminum SER cable installed in the attic of a one-family dwelling where the ambient temperature is 110 degrees F.
47.9 amperes
Size 6 AWG AL XHHW ampacity before correction = 55 amperes
55 amperes x .87 (temperature correction) = 47.85 amperes
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Unless specifically identified for a higher percentage of fill, the cross-sectional area of the conductors in a conduit seal shall NOT exceed ________ of the cross-sectional area of a rigid metal conduit of the same trade size.
25 percent
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Where a transformer is installed to supply a 243 ampere, 208-volt, 3-phase load the transformer must have a kVA rating of at LEAST ________.
90 kVA
First find the VA: 208 volts x 1.732 x 243 amperes = 87,542 VA
87,542 ÷ 1000 = 87.5 kVA
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Direct-buried cables or conductors located in a trench below two (2) inch thick concrete or equivalent shall have a MINIMUM cover requirement of ________.
18 inches
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The MAXIMUM unsupported length of Type MC cable used to supply a luminaire in an accessible ceiling is permitted to be NOT more than ________ in length.
6 feet
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The MAXIMUM required distance between trade size 2 in. rigid metal conduit supports is ________.
16 feet
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Where a submersible pump is located in a pond of a water treatment plant, the on land service equipment for the pump shall be NO closer than ________ horizontally from the shoreline.
5 feet
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For dwelling units, GFCI protection shall be provided for lighting outlets not exceeding 120 volts where installed in ________.
I. crawl spaces
II. bathrooms
I only
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Equipment supplied by Class 1 circuits such as fire alarm, control, and signaling circuits shall be grounded, UNLESS operating at less than ________.
50 volts
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A single-phase, 120/240-volt, 18 kW rated home standby generator has a full-load current rating of ________.
75 volts
I = power I/volts
= (18 kW x 1,000)/240 volts
= 18,000/240
= 75 amperes
Fill in the blank:
A premises wiring system supplied by a grounded ac electrical service, shall have a grounding electrode conductor connected to ________.
the grounded service conductor
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Intrinsically safe apparatus, associated apparatus, and other equipment shall be installed ________, unless the equipment is a simple apparatus that does not interconnect intrinsically safe circuits.
in accordance with the control drawings
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When a retail furniture store has 80 continuous linear feet of display show window, the NEC® mandates at LEAST ________ 125-volt, single-phase 15- or 20-ampere rated receptacle outlets shall be provided within 18 inches of the top of the show window for the show window lighting.
Seven
80 ft. (show window)/12 ft. (per receptacle)
= 6.7 = 7 receptacles
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Single grounding type receptacles, with GFCI protection that provide power for water pump circulation motors of permanently installed swimming pools shall be located at LEAST ________ from the inside walls of the pool.
6 feet
What MINIMUM size 75°C copper feeder conductors are required to supply the following group of 3-phase, 230-volt motors?
- one (1) 15 hp wound-rotor
- one (1) 71⁄2 hp induction-type
- one (1) 3 hp induction-type
4 AWG THWN
15 hp FLC - 42 amperes x 125% = 52.5 amperes
71⁄2 hp FLC - 22 amperes x 100% = 22.0 amperes
3 hp FLC – 9.6 amperes x 100% = 9.6 amperes
Total = 84.1 amperes
NOTE: Size 4 AWG THWN conductors with an ampacity of 85 amperes should be selected from Table 310.16.
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A transformer nameplate is NOT required to be marked with ________.
overcurrent protection
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In general, when current-carrying conductors are installed in parallel, the paralleled conductors in each phase shall ________:
I. be the same size in circular mil area
II. have the same insulation type
Both I and II
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In compliance with the rules set forth by the NEC®, conductors with type ________ insulation are not permitted for use in wet locations such as, where installed underground in a conduit or outdoors exposed to the weather.
THHN
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Where transformer vaults are not protected with an automatic fire-suppression system, they shall be constructed of materials that have a MINIMUM fire-resistance rating of ________.
3 hours
