Electrical Formula Part-1

Parallel Circuits :

• Total resistance is always less than the smallest resistor = 1/(1/R1+ 1/R2+ 1/R3+ ...1/Rn)
• Total current is equal to the sum of the currents of all parallel resistors
• Total power is equal to the sum of power of all parallel resistors
• Voltage is the same across each of the parallel resistors

Series Circuits : 

• Total resistance is equal to the sum of all the resistors =(R1+R2+R3+...Rn)
• Current in the circuit remains the same through all the resistors
• Voltage source is equal to the sum of voltage drops of all resistors
• Power of the circuit is equal to the sum of the power of all resistors

Considering 50Hz frequency:
Capacitive Reactance (Xc) in Ohms = 1/(2πf C)
Inductive Reactance (XL) in Ohms = 2π f L
Effective (RMS) AC Amperes = Peak Amperes x 0.707
Effective (RMS) AC Volts = Peak Volts x 0.707
Peak AC Volts = Effective (RMS) AC Volts x  2
Peak Amperes = Effective (RMS) Amperes x  2
Power Factor (PF) = Watts/VA
VA (apparent power) = Volts x Ampere or Watts/Power Factor
VA 1-Phase = Volts x Amperes
VA 3-Phase = Volts x Amperes x  3
Watts (real power) Single-Phase = Volts x Amperes x Power Factor
Watts (real power) Three-Phase = Volts x Amperes x Power Factor x3

Formula for Efficiency:
Input = Output/Efficiency
Output = Input x Efficiency
Efficiency in % = Output/Input x 100
Efficiency = Output/Input
Horsepower = Output Watts/746 

For more see:Electrical formula Part-II