NEC 2008 code
A 2-wire circuit is 0.5 miles long and consists of conductors which have a resistance of 0.125 ohm per 1000 feet. If 6 amperes flow in the circuit when 120 volts is applied, the percentage voltage drop will be most nearly in percent: a) 1.7 b) 2.5 c) 3.3 d) 6.8
Ans C) 3.3 Solution: Step 1: 2 x .5 miles = 5280 ft. Step 2: 5280/1000= 5.28 5.28 x 0.125= .66 ohms Step 3: VD = I X R = 6 amps x .66 ohms = 3.96 v Step 4: 3.96vd/120v = .033 or .033 x 100= 3.3
Feeder and service loads for fixed electric space heating shall be calculated at _____ percent of the total connected load. A) 80 B)100 C)125 D)200
Ans. (B) 100 Article 220.51
The point of attachment of overhead premises wiring to a building shall in no case be less than ___above finished grade. A) 8ft B) 10ft C) 12ft D) 15ft
Ans. (B) 10ft. Article 225.16 (a)
A battery that has an EMF of two volts and an internal resistance of 0.2 ohm causes a current of the ampere to flow through a load . The terminal voltage of the battery under these conditions is a) 0.2 b) 0.4 c) 1.8 d) 2.2
Ans: C) 1.8 Solution: Vd = I x R = 1 x .2 = .2 volts E line = EMF - Vd 2 - .2 = 1.8 volts
What size branch-circuit conductors are required for the underground conductors of a 44A continous load, if the equipment terminals are rated 75'C? (a) 10 AWG (b) 8 AWG (c) 6 AWG (d) 4 AWG
Ans: C) 6 AWG Article : 210.20 (A)(1) Solution: 75C conductors - 6AWG 44A x 1.25= 55A
The resistance in ohms, of a 25 ampere, 50 millivolts shunt is approximately: a) 2 b) .2 c) 0.02 d) 0.002
Ans: D) 0.002 Solution: R= E/I = .05/25= .002
the maximum length of a feeder tap conductor in a high-bay manufacturing building over 35 ft. high shall be___ a) 15 ft b) 20 ft c) 50 ft d) 100 ft
Ans: D) 100 ft. Article 240.21 (b)(4)
In clothes closets, recessed incandescent or LED luminairs with a completely enclosed lamp can be installed in the wall or the ceiling , proviede there is a minimum clearance of ___between the luminaire and the nearest point of a storage space. a) 3 in. b) 6 in. c) 9 in. d) 12 in.
Ans: D) 12 in. Article 410.16 (b)(1)
The minimum clearance for Service-drop conductors not exceeding 600V that pass over commercial areas subject to truck traffic is ____ a) 10 ft b) 12 ft c) 15 ft d) 18 ft
Ans: D) 18 ft Article 230.24 (b)(4)
The minimum clearance for overhead feeder conductors not exceeding 600V that pass over commercial areas subject to truck traffic is____ a) 10 ft b) 12 ft c) 15 ft d) 18 ft
Ans: D) 18 ft. Article 225.18
A single-phase load connected to a 220v line takes 30 amps and dissipates 5,280 watts. The power factor is: A) 50% B) 60% C) 70% D) 80%
Ans: D) 80% Solution: P/E x I x P.F. P.F. = 5280/220v X 30a= .8
The impedance of a coil varies a) directly with the frequency b) inversely with the frequency c) inversely with its inductance d) inversely with its resistance
Ans: A) directly with the frequency
The iron cores of transformers are laminated because this: a) reduces the Eddy-current b) increases the Hysteresis c) increase the turns ratio d) reduces the wight of the transformer
Ans: A) reduces the Eddy-current
The two to six disconnects for a disconnecting means for a building supplied by a feeder shall be _____. A)the same size B)grouped C)in the same enclosure D)none of these
Ans. (B) grouped Article 225.34 (a)
The maximum unbalanced feeder load for household electric ranges,wall-mounted ovens,and counter-mounted cooking units shall be considered as ____percent of the load on the ungrounded conductors. A)50 B)70 C)85 D)115
Ans. (B)70 Article 220.61 (b)(1) Table 220.55
When sizing a feeder for the fixed appliance loads in dwelling units, a demand factor of 75% of the total nameplate ratings can be applied if there are ____ or more appliances fastened in place on the same feeder. A) two B) three C) four D) five
Ans. (C) four Article : 220.53
The MINIMUM size Overhead Service -drop conductors shall not be smaller than _____copper or ____ aluminum.
Ans. 8 AWG copper 6 AWG aluminum Article 230.23 (b)
The MINIMUM size Underground Service-Lateral conductors shall not be smaller than ____ copper or ____aluminum.
Ans: 4 AWG copper 2 AWG aluminum Article 230.31 (B) Amendment.
When service-entrance conductors exceed 1,100 kcmil for copper, the required grounded conductor for the service shall be sized not less than___ percent of the area of the largest ungrounded service-entrance conductor. a) 12.5% b) 15 c) 19 d) 25
Ans: A) 12.5% Article: 250.24 (c)(1)
In a dwelling unit , each wall space ___ or wider requires a receptacle a) 2 ft b) 3 ft c) 4 ft d) 5 ft
Ans: A) 2 ft Article 210.52 (A)(2)(1)
If the circuit's overcurrent device exceeds ______,the conductor ampacity must have a rating not less than the rating of the overcurrent device. A) 800A B)1000A C) 1,200A D) 2000A
Ans: A) 800A Article 240.4 (c)
The size of the fuse to be used in a circuit depends upon the: a) connected load b) size of wire c) voltage of the line d) rating of the switch
Ans: A) connected load
Multiwire branch circuits shall___ (a) supply only line-to-neutral loads (b) not be permitted in dwelling units (c) have there conductors originate from different panel boards (d) none of these
Ans: A) supply only line-to-neutral loads Article: 210.4(c)
A 3 phase 120/208 volt lighting panel that is located 750 feet from its source, takes 30 kilo watts. If the volt drop is not to exceed 2.5% and k=10.4 ohms per mil foot, the size wire required is approximately: a) #2 AWG b) 215,000 CMA c) 300,000 CMA d) 400,000 CMA
Ans: B) 215,000 CMA Solution: P/1.73 x E x I x P.F. I= 30,000/1.73 x 208 x 1= 83 amps Step 2: Vd= 2.5% x 208= 5.2 volts Step 3: 1.73 x k x I x L / cma x vd cma= 1.73 x 10.4 x83 x 750/ 5.2 = 215,385 cma
Branch circuit conductors within___ of a ballast shall have an insulation temperature rating of not lower than 90'C (194'F). (a) 1 in. (b) 3 in. (c) 6 in. (d0 8 in.
Ans: B) 3 in. Article 410.68
The minimum working space on a circuit that is 120 volts to ground, with exposed live parts and no live or grounded parts on the other side of the working space , is _____ (a) 1ft (b) 3ft (c) 4ft (d) 6ft
Ans: B) 3ft Article 110.26 (a)(1)
What is the maximum fault current that can flow through the earth to the power supply from a 120v ground fault to metal parts of a light pole that is grounded via a ground rod having a contact resistance to earth of 25 ohms? A) 2 amps B) 4.80 amps C) 3.2 amps D) 5 amps
Ans: B) 4.80 amps Solution: I=E/R I= 120v/25 ohms I= 4.80A
A D.C. motor takes a full load current of 50A. A thermal cutout protecting the motor against overloads should be set to open the circuit for not more than: A) 60 amps B) 58 amps C) 62.5 amps D) 100 amps
Ans: B) 58 amps Article 430.32 (1) Solution : 50 X 115%= 57.5 amps
An instrument that measures electrical energy is the: a) current transformer b) watthour meter c) dynamometer d) wattmeter
Ans: B) Watthour meter