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.
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
