PE Review test 1

What is the burial depth of a 15kV direct buried cable?

30" NESC pg 236

The resistance between two ground rods with similar characteristics measure 30ohms if these gnd rods are jumpered together, what is the resistance between the rods and earth?

7.5ohms

Positive Sequence currents are: a. same magnitude, same phase b. same magnitude, phase 120 degree apart c. same mag, different phase

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per NEC standards vfd is rated at 19.9 amps per NEC standards what is the breaker rating for vfd?

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per NEC standards what is the setting for the ground fault for service entrance of 480 volts? a. 2400A b. 1200A c. 3000A

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Two transformers are parallel connected in a fault occurs t1 is equal to 0.08 per unit and T2 is equal to 0.09 per unit which transformer will have more fault current?

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per NEC standards, what is the minimum distance for multiple ground electrodes?

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A motor is fed from a vfd rectifier. what would happen to the system if the vfd voltage is maintained and there is an increase in vfd frequency? a. decrease in magnetic flux b. decrease or increase in torque c. decrease or increase in speed

Current Decreases as frequency increases. Therefore decreases available Torque

How do you size an MCP?

MCP provides short circuit protection NEC 430.52***** look into this more

A $100k balloon payment will be made in 4 years. At 12% interest, find the present value.

P= (100) (p/f, 12%, 4)

What Power Quality term descrobes a transient of short duration and high magnitude?

Surge

find the voltage drop of the conductor if the current is 40 A the length is 400 ft the conductor is # 6 AWG copper uncoated and it's single phase. reactance can be ignored

VD= ????

In a single line to ground fault which of the following is true? a. 0 sequence flows b. positive sequence flows c. 0, positive, negative sequence flows d. negative flows

Zero, Positive, and negative flow

Which of the following device will help prevent electrical shock on a 120V circuit? a. GFCI b. AFCI c. CB d. Fuse

a. GFCI

For a delta system what is the minimum number of PTs and CTs for billing? a. 1PT/1CT b. 2PTs/2CTs c. 2PTs/3CTs d. 3PTs/3CTs

b. 2PTs/2CTs

An apparatus is designed to be dust tight. What classification of hazardous locations can this apparatus be installed at? a. Class II, Division 1 b. Class II, Division 2 c. Class I

b. Class II, Division 2; NEC 500.5, 500.7

A motor is fed from a VFD rectifier. What would happen to the system if the VFD voltage is maintained and increase VFD frequency? a. decrease mag flux b. decrease/increase torque c. decrease/increase speed

flux = v/f . If Freq ↑, mag flux↓ and Torque ↓

Find internal rate of return with a 75k investment today, 90k payback after 3 years

i= 6.3% 75=90(1+i)^ -3

A serivce is fed by 4 sets of 500kcmil conductors, 4 per phase, through four different sets of steel conduits. What is the appropriate sized grounding conductor? a. four 3/0 gnd conductors, one in each conduit b. one 3/0 gnd conductor in one of the conduits

one 3/0 gnd conductor in one of the conduits

A 10V to 100V DC step up circuit is shown. 100W is drawn. Find the current through the diode

1 amp

NEC What is the max deya allows of a CB to trip to 3000A to gnd fault?

1 second NEC 230.95

A generator provides emergency power to a public building. After a power loss, what is the max amount of time allowed until emergency power is supplied?

10 seconds NEC 700.12

What an NEMA standard cabinet should be used for oil or coolant spraying and splashing environment with an indoor condition?

13

four lines are connected to a ring bus if a fault occurs on one of the lines how many circuit breakers will trip?

2

What is the required gnd electride conductor size for a service fed by four sets of 250kcmil conductors, 4 per phase?

2/0 Table 250 4*250kcmil=1000kcmil

what is the maximum distance you can put a receptacle GFCI by a pool?

20 ft

the self discharge rate of a battery is least affected by? a. concentration (specific gravity) of electrolyte b. age of battery c. temperature d. nominal voltage of the battery or terminal voltage of the battery

Nominal Voltage of Battery

Positive sequence current are: a. same magnitude, same phase b. same magnitude, phase 120° apart c. same magnitude, different phase

Equal Magnitudes, Equal Displacement angles (120 degrees apart)

A synchronous generator outputs reactive power. How do you increase the output of MVARs

Increase field current

How to get rid of noise/harmonics on VFD?

Increase the switching Frequency of the vfd

If the spacing of conductors in transmission line increases, what will decrease? a. inductance b. capacitance c. GMD d. resistivity

Line Capacitance will will decrease, Line Inductance will increase.

What is the relationship of the losses to the load for a squirrel cage motor?

Load Losses are square to the load plus no-load losses

What is the max size inverse time CB required to protect a 480V circuit with the following loads: Lighting 10kVA Heating 15kW Design Motor B 25kVA?

NEC 430.53 Light: 10kva/[480*sqrt3]=12A*125% (continuous)=15A Heat: 15kW/[480*sqrt3]= 18A*100% (non-cont)= 18A Des B: 25kVA/[480*sqrt3]=30*250%=75A Total: 108A --> next size CB 110A

A 4-pole induction motor is loaded to a torque of 50NM with a slip of 2.3%. What is the speed if the load is added such that the torque is increased to 100NM?

1720 RPM 50nm/100nm= 2.3%/S S=4.6% .046=1800-nr/1800-->nr

Which NEMA standard cabinet should be used for oil and coolant spraying and splashing environment with indoor condition?

13 (check)

Find the maximum spacing of lamps given: Lamps placed 12 feet high along a 30ft wide alley. 1 ft-candle illumination. Given Lumens/lamp, CU, LLD, LLF

40 1fc= (n*Lxc)/A ---->> A= W x L

what method is not practiced in modeling the power flow for voltage bus? a. shunting capacitor b. changing transformer top

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To increase the electrical safety of an outlet located near water, a gnd fault circuit interrupter (GFCI) is used. in this situation, which of the following is the least likely reason a typical CB provides inadequate protection for individuals using this outlet: a. CBs do not open when there is an imbalance in current in the hot and neutral wires b. CBs are typically used to protect equipment and help prevent conductors from overheating and humans from electrical shock c. CBs are usually break at a current level much greater than the let-go current d. CBs trip too quickly

CBs trip too quickly

The field of a DC generator is normally located at the

Stator

Find the power of the motor. V=208. Equivalent circuit shown. slip is 5% 208V, # poles, Rth, Xth, and X2 given. What is the power delivered to the motor?

Torque= Pout/w= (3I²R)/ω = 3*R*1/ω* V²/[(Rtotal)²+Xtotal² ]

What does GFCI read? a. Line and Neutral b. Line and Ground c. Ground to Neutral d. none of the above

a. Line and Neutral NEC 210.8

Given the torque speed curve of an induction motor which region is the steady state region?

to the right of the peak.

An autotransformer feeds an induction motor half of its rated voltage to reduce the starting torque. how is the starting torque affected?

torque is reduced to 1/4 of the starting torque

An autoxfmr is used to start a motor at 40% of the motor's rated voltage to reduce the starting torque. What is the starting torque of the motor if it is started at 40% of its rated voltage?

torque ₄₀%= 16% * torque starting

A xfmr is operating at max efficiency. Its output is 30kW. Core losses equal 900W. Find efficiency of the xfmr. (THE ANSWER IS IN LINHS TESTS)

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Given the following circuit: CB-line with CT to 51,51N- XFMR Delta-Wye GND- 12kV bus- 12kV feeder feeding only loads. Why is the gnd fault protection set to a minimum? a. Coordination b. no coordination c. High gnd fault current d. Low gnd fault current

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In the 3P system, 13.8kV delta/ 13.8kV why rated at 230kVA. The test voltage 830V is to be applied to the high side of the transformer to determine the per unit impedance of the xfmr. a. 10% b. 6% c. 2% d. 1%

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per NEC standards, what size of conduit should be used if it is to fill for four space 300 kcmil, one full neutral conductor and 1/0 ground conductor

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NEC - Four 500kcmil in a conduit serve a 3P 4W harmonic load. Find the ampacity of the cable

??? Multiply by 0.8 for cable bundling derating. The neutral is counted as a live wire since harmonic currents are flowing.

Which measurement will not work? a, Measure voltage across a load b. Measure voltage in parallel with load c. Measure current in parallel with a load d. Measure current in series with a load

C. Measure current in parallel with a load

A motor fed by a 5k HZ vfd rectifier is making a high-pitched objection noise what is the best method to eliminate the noise? a. increase the line distance between vfd and motor b. decrease the line distance between vfd and motor c. increase the switching frequency of vfd d. add reactor on the line side of vfd

c. increase the switching frequency of vfd

The main service panel for residential service is located in the home's basement. A subpanel is located in the attached garage, the two panels are connected using a number 6 AWG cable containing two hot wires a neutral and one ground wire. From the standpoint of safety the best grounding method is to: a separately and locally Earth ground both the main panel and subpanel, and then connect the corresponding end of the cables ground wire to these local Earth grounds b. provide the connections as given an A and for added safety splice the cable Midway and locally ground the cables ground wire at the splice location c. locally Earth ground the main panel and connect the corresponding end of the ground wire to the main panels chassis however do not locally Earth ground the sub panel but connect the corresponding end of the cables ground wire to the sub panels chassis d. do not earth ground either the main panel or the subpanel but instead connect the corresponding end of the cables ground wire to the nearest hot water pipe and use a GFCI at both the main panel and the sub panel

c. locally Earth ground the main panel and connect the corresponding end of the ground wire to this main panels chassis however do not locally Earth ground the subpanel but connect the corresponding end of the cables ground wire to the sub panels chassis