Memory Formula

25Nov/09Off

Memory Formula

Where can I Find an Electrical Formula List?

I'm looking for somewhere i can print out a lost of Electrical Formulas. Although I am hoping that it's the formulas with a description next to them and maybe an explanation as to how to do them. I've done a few of the formulas but I don't have any of them commited to memory and can't find a good place to get them in a way i can understand it better. So any websites with Electrical formulas and explanations of them, or if an experienced electrician would write them for me(which is A LOT to write) that would be great. Thanks

E = Voltage / I = Amps /W = Watts / PF = Power Factor / Eff = Efficiency / HP = Horsepower
AC/DC Formulas
To Find Direct Current AC / 1phase
115v or 120v AC / 1phase
208,230, or 240v AC 3 phase
All Voltages
Amps when
Horsepower is Known HP x 746
E x Eff HP x 746
E x Eff X PF HP x 746
E x Eff x PF HP x 746
1.73 x E x Eff x PF
Amps when
Kilowatts is known kW x 1000
E kW x 1000
E x PF kW x 1000
E x PF kW x 1000
1.73 x E x PF
Amps when
kVA is known kVA x 1000
E kVA x 1000
E kVA x 1000
1.73 x E
Kilowatts I x E
1000 I x E x PF
1000 I x E x PF
1000 I x E x 1.73 PF
1000
Kilovolt-Amps I x E
1000 I x E
1000 I x E x 1.73
1000
Horsepower
(output) I x E x Eff
746 I x E x Eff x PF
746 I x E x Eff x PF
746 I x E x Eff x 1.73 x PF
746

Three Phase Values
For 208 volts x 1.732, use 360
For 230 volts x 1.732, use 398
For 240 volts x 1.732, use 416
For 440 volts x 1.732, use 762
For 460 volts x 1.732, use 797
For 480 Volts x 1.732, use 831

E = Voltage / I = Amps /W = Watts / PF = Power Factor / Eff = Efficiency / HP = Horsepower
AC Efficiency and Power Factor Formulas
To Find Single Phase Three Phase
Efficiency 746 x HP
E x I x PF 746 x HP
E x I x PF x 1.732
Power Factor Input Watts
V x A Input Watts
E x I x 1.732

Power - DC Circuits
Watts = E xI
Amps = W / E

Ohm's Law / Power Formulas
P = watts

I = amps

R = ohms

E = Volts
E=IR
P=I^2*R

Voltage Drop Formulas
Single Phase
(2 or 3 wire) VD = 2 x K x I x L
CM K = ohms per mil foot

(Copper = 12.9 at 75°)

(Alum = 21.2 at 75°)
Note: K value changes with temperature. Look up the necessary values from books.

L = Length of conductor in feet

I = Current in conductor (amperes)

CM = Circular mil area of conductor
CM= 2K x L x I
VD
Three Phase VD= 1.73 x K x I x L
CM
CM= 1.73 x K x L x I
VD
Calculating Motor Speed:

A squirrel cage induction motor is a constant speed device. It cannot operate for any length of time at speeds below those shown on the nameplate without danger of burning out.

To Calculate the speed of a induction motor, apply this formula:

Srpm = 120 x FP

Srpm = synchronous revolutions per minute.
120 = constant
F = supply frequency (in cycles/sec)
P = number of motor winding poles

Example: What is the synchronous of a motor having 4 poles connected to a 60 hz power supply?

Srpm = 120 x FP

Srpm = 120 x 60

Srpm = 7200

Srpm = 1800 rpm

1. Voltage and Current: Primary (p) secondary (s)
Power(p) = power (s) or Ep x Ip = Es x Is
A. Ep = Es x Is
Ip B. Ip = Es x Isx Ep

C. Is = Ep x Ipx Es

D. Es = Ep x Ip x Is

2. Voltage and Turns in Coil:
Voltage (p) x Turns (s) = Voltage (s) x Turns (p)
or Ep x Ts = Es x Ip
A. Ep = Es x Ip
Ts B. Ts = Es x Tp
Ep