calculations

Question 1

Voltage drop of two #12 Conductors (.40ohms) supplying a 16a load 100’ away

Answer 1

IxR

16a X .40 = 6.40a

Question 2

What is the resistance of a circuit conductor when the conductor voltage drop is 7.20v and the current flow is 50a

Answer 2

E/I

7.20 / 50a = .144ohms

Question 3

What is the power loss in watts of a conductor that carries 24A and has a voltage drop of 7.20V

Answer 3

IxE

24A X 7.20V= 172w

Question 4

What is the approximate power consumed by a 10KW heat strip rated @ 230v, When connected to a 208v circuit

Answer 4

230vx230x / 10,000 =5.29ohms
208x208 / 5.29 = 8,178 / 10000 = 8.20KW
Answer 8KW

Question 5

The total circuit resistance of two 12 AWG conductors (each 100’ long is .40ohms. If the current of the circuit is 16a
What is the power loss of the conductors

Answer 5

Isquared X R = (16ax16a)X(.40) = 102.4

100watts

Question 6

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

Answer 6

P=I X R
E= 120v X 3% (.03) = 3.60v
12a X 3.60v
Power = 43.20

Question 7

What does it cost per year (at 8cents per KWh) for the power loss of a 12 AWG circuit conductor (100’ long) that has a total resistance of .40ohms and a current flow of 16a

Answer 7

Power per Hr = I squared X R
Power per Hr = 102.4
102.40 X 24=2457.6 X 365 = 897024( hours per year) / 1000 = 897kwh X .08 = $71.76

Question 8

What is the power consumed by a 10KW heat strip rated 230v connected to a 115v circuit

Answer 8

P= E squared / R
230v x 230v / 10,000watts 
P= 5.29watts 
Connected voltage 115 X 115 / 5.29w = 2500
2500/ 1000 = 2.5KW

Question 9

To find Kw from watts divide by _______

Answer 9

1,000

Question 10

125% in decimal form is

Answer 10

1.25

Question 11

250% in decimal form is

Answer 11

2.50

Question 12

An over current protection devise must be sized no less then _______ % of the continuous load

Answer 12

125

Question 13

Increase the whole number 45 by 35%

Answer 13

.35 add 1 = 1.35 x 45 = 60.75

Question 14

To find the reciprocal

Answer 14

Divide the number 1 / (percentage)

Question 15

Formula for area is

Answer 15

Pie x r squared (Radius is 1/2 the diameter)

3.14 x the radius squared

Question 16

3 phase multiplier

Answer 16

1.73

Question 17

What is the current of a 36,000w @ 208 volt

Answer 17

208 x 1.73=359.84
36,000w / 359.84
100a

Question 18

Cubic inches Length x Width x depth

Example 4sq box that is 1-1/2” deep

Answer 18

4x4x1.50=24 Cu In

Question 19

To find watts from Kw multiply by _______

Answer 19

1000

Question 20

The input of a transformer is 300w The transformers efficiency is 90% Since output is always less then input because of efficiency, what is the transformer output

Answer 20

240w

Question 21

Electron current flows from _______ to ________

Answer 21

negative to positive

Question 22

What is the voltage drop over two 12 AWG conductors (resistance is .20 per 100’) supplying a 16a load located 50’ ft from the power supply

Answer 22

E vd = I X R
16a x .10 (50’)
1.6 +1.6 for second wire
3.2v

Question 23

What is the resistance of the circuit conductors when the conductor voltage drop is 3v and the current flowing in the circuit is 100a

Answer 23

R= E/I
3/100
.03

Question 24

What is the current flow in amperes through a 7.5kw heat strip rated at 230v. When the load is connected to 230v

Answer 24

Change 7.5kw to watts (7500)

7500/230=32.6a

Question 25

What is the conductor power loss in watts for a 10 AWG conductor that has a voltage drop of 3 percent and carries a current flow of 24a

Answer 25

240v x .03 = 7.2 vd

24a x 7.2v=172w