ELECTRICAL ENGINEERING FORMULAS

DIRECT CURRENT(DC)

I = current(amps.), V = voltage(volts), R = resistance(ohms), P = power(watts)

• CURRENT:

I = V/R or I = P/V    

• VOLTAGE:

          V= P/I or V = IR  

• POWER:

          I²R or VI       

• RESISTANCE:

          R = V/I   

ALTERNATING CURRENT(AC)

Il = line current(amps.), Ip = phase current(amps.), Vp = phase voltage(volts), Vl = line voltage(volts), Z = impedance(ohms), P = power(watts)

f = power factor(angle), VAR = volt-ampers

• CURRENT(single phase):

         I = P/(Vp cos(f)

• CURRENT(3 phase):

          I = P/√3(Vl cos(f)) or I = P/3(Vp cos(f))

• POWER(single phase):

          P = (VpIp cos(f))

• POWER(3 phase):

          P = √3(VlIl cos(f)) or P = 3(VpIp cos(f))