Unit 5: Box and Raceway Sizing Flashcards
Applying NEC® requirements to determine the proper sizing of outlet, junction, and pull boxes, as well as raceways, ensuring adequate space for conductors and compliance with code regulations. (25 cards)
Fill in the blank:
Where flexible cord is used as the wiring method to supply ac motors,the required size of the conductors shall be selected in accordance with _____ of the NEC.
Section 400.5
Fill in the blank:
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
Fill in the blank:
When used outdoors and ambient temperature is not a factor, size 6/3 w/g Type UF cable has an ampacity of _____.
55 amperes
Fill in the blank:
Shore power for boats shall be provided by single receptacles rated not less than ____\__.
30 amperes
Fill in the blank:
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
Fill in the blank:
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
Fill in the blank:
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
D 3-phase Power Formula
First find the VA: 208 volts x 1.732 x 243 amperes = 87,542 VA
87,542 ÷ 1000 = 87.5 kVA
Fill in the blank:
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
Fill in the blank:
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
Fill in the blank:
The maximum permitted distance between supports of straight horizontal runs of threaded trade size 2 in. rigid metal conduit is _____.
16 feet
Fill in the blank:
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
When splicing existing underground service conductors to extend to a new service location, the NEC requires:
I. the use of splice boxes
II. the conductors to be protected with a covering of at least two (2) inches of concrete
neither I nor II
Fill in the blank:
Equipment supplied by Class 1 circuits such as fire alarm, control, and signaling circuits shall be grounded, unless operating at less than _____
50 volts
Fill in the blank:
A single-phase, 120/240-volt, 18 kW rated home standby generator has a full-load current rating of _____ .
75 amperes
A Single-Phase Current Formula
I = power I = 18 kW x 1,000 = 18,000 = 75 amperes
volts 240 volts 240
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
Fill in the blank:
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
Fill in the blank:
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) = 6.7 = 7 receptacles
12 ft. (per receptacle)
Fill in the blank:
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 75oC copper feeder conductors are required to supply the following group of 3-phase, 208-volt motors?
- one (1) 15 hp wound-rotor
- one (1) 71⁄2 hp induction-type
- one (1) 3 hp induction-type
3 AWG THWN
15 hp FLC - 46.2 amperes x 125% = 57.75 amperes
71⁄2 hp FLC - 24.2 amperes x 100% = 24.20 amperes
3 hp FLC – 10 .6 amperes x 100% = 10.60 amperes
Total = 92.55 amperes
*NOTE: Size 3 AWG THWN conductors with an ampacity of 100 amperes should be selected from Table 310.16.
Which of the following is not required to be marked on the nameplate of a dry-type transformer?
a. kVA rating
b. manufacturer
c. voltage
d. overcurrent protection
d. overcurrent protection
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
Fill in the blank:
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
Fill in the blank:
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
