Electrical Fundamentals and Formulas Flashcards
Power Factor is?
The ratio between true power (W) and apparent power (VA). PF= W/VA
The two forms of Reactance are?
XL= Inductive {a coil}
XC= Capacitive {a capacitor}
When 2 resistances are connected in series_______?
Current in each resistor will be the SAME.
Current in a capacitive circuit______?
Leads the applied voltage in time.
Motor Efficiency =
Power Efficiency =
Eff = HP X 746 / 1.73 X E X I X pf
Power out/ Power In
Current (I) in an inductive circuit
Lags voltage
True Power (W)
W = E x I x pf
Power Factor
PF = W / VA
Resistance (R)
E / I
E x E / W
w / I x I
Current (I)
E / R
W / E
Sq root of W / R
Voltage (E)
I x R
W / I
SQ root of W x R
Watts
E x I
I x I x R
E x E / R
Formula for unequal parallel resistors?
R1 x R2 / R1 + R2
The sum os series voltage drops ____?
equals the applied voltage.
Total resistance in parallel is _________ than any one resistance.
Less
In an AC wave, 30* of phase is ________ of a cycle.
360* / 30* = 12
1/12 sec
In a 60 cycle system, what length of time does it take to go 90*?
90* / 360* = .25
60 cycles / .25 = 240
1 / 24 seconds
Power Formula
Watts = Amps x Voltage x Pf
1ph: P = I x E x pf
3ph: P = 1.73 x I x E x pf
Total Voltage Drop for a circuit
Vdrop = 2 x I x R
3ph Vdrop = 1.73 x I x R
1 Horse Power
Hp = 746 watts
Current from Watts formula
I = W / E
Watts divided by Volts
Full Load Current for equipment Formula
I = kVA x 1000 / Volts
I = kVA x 1000 / 1.73 x Volts
The unit hertz is equal to
cycles per second
When voltage & current appear at their zero and peak values at the same time.
They are In-phase
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?
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
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?
- Rt = R1 + R2 (Rt = 560 + 240) =800
- find current ( same in series) I = 120 x 800 = .15A
- V2 = .15A X 240 = 36V
V = 36V
A 1ph resistance type strip heater is energized at 120V and has a rating of 4500W. What will the strip heater draw?
I = W/E
I = 4500 / 120V
I = 37.6 A
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?
Vdrop = 2 x K x I x L / Area
Vdrop = 2 x 12 x 26A x 200ft / 10,380cmil
Vdrop = 12.9V
Table 8, CH 9- 10AWG =
