Electrical Fundamentals and Formulas

Question 1

Power Factor is?

Answer 1

The ratio between true power (W) and apparent power (VA). PF= W/VA

Question 2

The two forms of Reactance are?

Answer 2

XL= Inductive {a coil}
XC= Capacitive {a capacitor}

Question 3

When 2 resistances are connected in series_______?

Answer 3

Current in each resistor will be the SAME.

Question 4

Current in a capacitive circuit______?

Answer 4

Leads the applied voltage in time.

Question 5

Motor Efficiency =
Power Efficiency =

Answer 5

Eff = HP X 746 / 1.73 X E X I X pf
Power out/ Power In

Question 6

Current (I) in an inductive circuit

Answer 6

Lags voltage

Question 7

True Power (W)

Answer 7

W = E x I x pf

Question 8

Power Factor

Answer 8

PF = W / VA

Question 9

Resistance (R)

Answer 9

E / I
E x E / W
w / I x I

Question 10

Current (I)

Answer 10

E / R
W / E
Sq root of W / R

Question 11

Voltage (E)

Answer 11

I x R
W / I
SQ root of W x R

Question 12

Watts

Answer 12

E x I
I x I x R
E x E / R

Question 13

Formula for unequal parallel resistors?

Answer 13

R1 x R2 / R1 + R2

Question 14

The sum os series voltage drops ____?

Answer 14

equals the applied voltage.

Question 15

Total resistance in parallel is _________ than any one resistance.

Answer 15

Less

Question 16

In an AC wave, 30* of phase is ________ of a cycle.

Answer 16

360* / 30* = 12
1/12 sec

Question 17

In a 60 cycle system, what length of time does it take to go 90*?

Answer 17

90* / 360* = .25
60 cycles / .25 = 240
1 / 24 seconds

Question 18

Power Formula

Answer 18

Watts = Amps x Voltage x Pf
1ph: P = I x E x pf
3ph: P = 1.73 x I x E x pf

Question 19

Total Voltage Drop for a circuit

Answer 19

Vdrop = 2 x I x R
3ph Vdrop = 1.73 x I x R

Question 20

1 Horse Power

Answer 20

Hp = 746 watts

Question 21

Current from Watts formula

Answer 21

I = W / E
Watts divided by Volts

Question 22

Full Load Current for equipment Formula

Answer 22

I = kVA x 1000 / Volts
I = kVA x 1000 / 1.73 x Volts

Question 23

The unit hertz is equal to

Answer 23

cycles per second

Question 24

When voltage & current appear at their zero and peak values at the same time.

Answer 24

They are In-phase

Question 25

3 electric devices are connected in parallel on a circuit with the first device having a restance of 6 ohm, the second having a resistance of 10 ohms, and the third having a resistance of 15 ohms. What is the total resistance?

Answer 25

Rt = R1 x R2 / R1 + R2 Rt = 6 x 10 / 6 + 10 Rt = 60 / 16 = 3.75 Rt = 3.75 x 15 / 3.75 + 15 Rt = 56.25 / 18.75 = 3 Rt = 3 ohms

Question 26

2 light bulbs are connected in series and supplied at 120 V. 1 light has a resistance of 560 ohms and the other has a resistance of 240 ohms. The voltage across the lamp with 240 ohms is?

Answer 26

1. Rt = R1 + R2 (Rt = 560 + 240) =800 2. find current ( same in series) I = 120 x 800 = .15A 3. V2 = .15A X 240 = 36V V = 36V

Question 27

A 1ph resistance type strip heater is energized at 120V and has a rating of 4500W. What will the strip heater draw?

Answer 27

I = W/E I = 4500 / 120V I = 37.6 A

Question 28

A single phase electric motor draws 28A and is supplied by a 10AWG stranded uncoated copper conductor. The length of the circuit from the panel to the motor is 200ft. What is the voltage drop when the motor s running?

Answer 28

Vdrop = 2 x K x I x L / Area Vdrop = 2 x 12 x 28A x 200ft / 10,380cmil **Vdrop = 12.9V** | Table 8, CH 9- 10AWG =