Delmar's Standard Textbook of Electricity 4th. Edition by Stephen L. Herman | 9781418065805 | 1418065803

Basic Electrical

Delmar's Standard Textbook of Electricity

7 SOLVED PROBLEMS

99 SOLVED PROBLEMS

Question: 25.1

Assume that the RLC parallel circuit shown in Figure 25–2 is connected to a 240-V, 60-Hz line. The resistor has a resistance of 12 Ω, the inductor has an inductive reactance of 8 Ω, and the capacitor has a capacitive reactance of 16 Ω. Complete the following unknown values: Z—impedance of the ...

Verified Answer:

Impedance The impedance of the circuit is the reci...

Question: 11.8

An electric annealing oven is located in an area with an ambient temperature of 125°F. The oven contains a 50-kW electric heating element and is connected to 480 volts. The conductors are to be copper with type THHN insulation. The termination temperature is not known. The furnace is expected to ...

Verified Answer:

Determine the amount of current needed to operate ...

Question: 8.2

Both of the preceding circuits were solved by first determining which parts of the circuit were in series and which were in parallel. The circuits were then reduced to a simple series or parallel circuit. This same procedure can be used for any combination circuit. The circuit shown in Figure 8–9 ...

Verified Answer:

The first step is to reduce the top part of the ci...

Question: 11.14

A three-phase motor is located 175 ft from its source of power. The conductors supplying power to the motor are 1/0 AWG aluminum. The motor has a full-load current draw of 88 A. What is the voltage drop across the conductors when the motor is operating at full load? ...

Verified Answer:

E_{D} = \frac{1.732 \times 17 \Omega-CM/...

Question: 11.2

Can Type THHN insulation be used in wet locations? ...

Verified Answer:

Locate Type THHN insulation in the second column. ...

Question: 21.3

An AC oil-filled capacitor has a voltage rating of 300 WVDC. Will the voltage rating of the capacitor be exceeded if the capacitor is connected to a 240-V, 60-Hz line? ...

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The DC voltage rating of the capacitor indicates t...

Question: 21.2

A capacitor is connected into a 480-V, 60-Hz circuit. An ammeter indicates a current flow of 2.6 A. What is the capacitance value of the capacitor? ...

Verified Answer:

The first step is to calculate the value of capaci...

Question: 32.3

An 800-hp, three-phase squirrel-cage motor is connected to 2300 V. The motor has a code letter of J. What is the starting current of this motor? ...

Verified Answer:

Table 430.7(B) of the NEC gives a value of 7.1 to ...

Question: 30.2

A DC motor is connected to a 120-VDC line and has a current draw of 1.3 A. The motor is operating a load that requires 8 lb-in. of torque and is turning at a speed of 1250 RPM. What is the efficiency of the motor? ...

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The first step is to determine the horsepower outp...

Question: 21.2

A small indicating lamp has a rating of 2 W when connected to 120 V. The lamp must be connected to a voltage of 480 V at 60 Hz. A capacitor will be connected in series with the lamp to reduce the circuit current to the proper value. What value of capacitor will be needed to perform this job? ...

Verified Answer:

The first step is to determine the amount of curre...

Question: 16.3

An inductor with negligible resistance is connected to a 480-V, 60-Hz line. An ammeter indicates a current flow of 24 A. How much current will flow in this circuit if the frequency is increased to 400 Hz? ...

Verified Answer:

The first step in solving this problem is to deter...

Question: 15.9

A half-wave rectifier is connected to 277 VAC. What is the average DC voltage? ...

Verified Answer:

average = RMS ×

\frac{0.9}{2}

avera...

Question: 15.6

A sine wave has a peak value of 354 V. What is the RMS value? ...

Verified Answer:

RMS = peak × 0.707 RMS = 354 V × 0.707 RMS = 250.2...

Question: 13.1

A coil has an inductance of 1.5 H and a wire resistance of 6 Ω. If the coil is connected to a battery of 3 V, how long will it take the current to reach its full Ohm’s law value of 0.5 A (3 V/6 Ω = 0.5 A)? ...

Verified Answer:

To find the time of one time constant, use the for...

Question: 2.1

An elevator must lift a load of 4000 lb to a height of 50 ft in 20 s. How much horsepower is required to operate the elevator? ...

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Find the amount of work that must be performed, an...

Question: 2.4

An electric hair dryer has a power rating of 1000 W. How much current will it draw when connected to 120 V? ...

Verified Answer:

The quantity to be found is amperage, or current. ...

Question: 2.5

An electric hotplate has a power rating of 1440 W and a current draw of 12 A. What is the resistance of the hotplate? ...

Verified Answer:

The quantity to be found is resistance, and the kn...