Exam Practice Help

Static Design

I posted this up in another thread but go no response. Can you answer these and show the math? from Holts practice exams.

What does it cost per year (at 8 cents per kWh) for the power loss of a 12 AWG circuit conductor (100 ft long) that has a total resistance of 0.4Ω and current flow of 16A?

1. $30

1. $50

1. $70

1. $90

What is the conductor power loss in watts for a 120V circuit that has a 3 percent voltage drop and carries a current flow of 12A?

1. 43W

1. 86W

1. 172W

1. 1,440W

The total circuit resistance of two 12 AWG conductors (each 100 ft long) is 0.4Ω. If the current of the circuit is 16A, what is the power loss of the conductors in watts

1. 75W

1. 100W

1. 300W

1. 600W

mickeyco

Four electricians are given one pie cut into eight slices, one of the electricians is Celtic, how many slices does each electrician get?




.

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TxElectrician

forget the question...where the heck is the ohm key on my computer?

Magnettica

Alt/ Option + Z = Ω

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480sparky

OK, so where's the Option key?

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rbsremodeling

on my computer it is alt/option = Q = Ω. are you using a MAC?

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Magnettica

What does it cost per year (at 8 cents per kWh) for the power loss of a 12 AWG circuit conductor (100 ft long) that has a total resistance of 0.4Ω and current flow of 16A?

It's been a couple of years for me but I have to know this for the exam so here goes.

VD (Voltage Drop) = KxIxL/ A (or CM) for 1Ø

K =10.4 for copper
I = 16 amps
L = Length
A = 0.4Ω

KxIxL/ A (or CM) = 41,600

0.008 = 8 cents per kilowatt hour

41,600/ 0.008= ????

I'm lost, someone please help, I forgot how to do this calculation.

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Magnettica

Of course, doesn't everyone use a Mac?

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Magnettica

What is the conductor power loss in watts for a 120V circuit that has a 3 percent voltage drop and carries a current flow of 12A?

12A x 120V = 1440W

1440W/3% = 43.2W

43 watts

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Magnettica

The total circuit resistance of two 12 AWG conductors (each 100 ft long) is 0.4Ω. If the current of the circuit is 16A, what is the power loss of the conductors in watts?

0.4 x 16 = 6.4

16 x 6.4 = 102.4

100 watts

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Static Design

Thanks for the help, I am still trying to figure out number 1.

TinkerGA

To answer your first question :
$70
Cost per year = Power for year in kWh x $o.o8
Use pie chart
P= I (squared) x R
I = 16A
R = .04 (ohms) This is estimated actually .396
Power per hour = (16A x 16A) x 0.4(ohms)
Power per hour = 102.4W
Power for the year in kWh = (102.4W x24 hours x 365 days)/1,000
Power for the year in kWh = 897 kWh
Cost per year in = 897 kWh x $0.08
Cost per Year =$71.76


Gave .4 as resistance NEC Chapter 9 table 8 gives ohms in kft uncoated for 12 awg is 1.98 (divide 1.98 by 1,000 ft. ) that give you ohms per foot. then multiply that by 100 ft. and multiply by 2 for 2 conductors = .396 ohms


Next question :

the answer is 43W =
P=IxE

I = 12A
E= 120V x 3%
E= 3.6 V

P= 12A x 3.6V
P= 43.2W

Next question :

answer 100W
P = I(squared) x R
I = 16A
R = 0.4ohms ( refer to question 1)
P= (16A x 16A) x 0.4ohms
P= 102.4W

Use the pie wheel. All power loss of conductors in theory is wasted electricity not used, most commonly known as resistance in wire.

Static Design

Why are you dividing by 1000?

rbsremodeling

kilowatt = 1000 watts.


what test are you studying for?

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Static Design

I got it now, I was dumb founded for a minute.

I am thinking about the electrical exam in the future, I haven't dealt with this stuff in years so I am trying to sharpen my electric theory skills before taking the plunge.

Magnettica

Welcome to the forum!

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Tinstaafl

Paradox alert!

If Celtic is an electrician, and by definition Celtic gets all the pies, other electricians get none. Therefore, each electrician's share=2(Celtic/4(3*0)), which by any math equals less than zero.

Magnettica

I had to laugh because I just got MH's exam prep book and these are questions 50, 51, and 52 in the book. Good thing I answered them correctly.