OFFICE
FACTORY
242/44 Moo 3
106/39 Moo 5
T. Phala A. Ban Chang
T.Plutaluang A.Sattahip
Rayong 21130
Chonburi 20180
THAILAND
THAILAND
PH: +66 (0)84 325 8889 (English) +66 (0)86 1130027 (Thai) FAX: +66 (0)38 602244
EMAIL: info@vikingpowersystems.com
www.vikingpowersystems.com
Common Electrical formulas
Ohm's Law
The basic relationships are:
volts = amps x ohms
watts = volts x amps
ohms = volts / amps
Impedance
Capacitive impedance (XC) is measured in ohms
XC = 1 / ( 2 f C), when f in frequency in Hz and C is capacitance in farads
Inductive impedance (XL) is measured in ohms
XL = 2 f L, when f in frequency in Hz and L is inductance in henrys
Resistive load
This is normally measured in Kilowatts (kW).
Ohm’s law for a simple resistive load
amps = volts / ohms
kW = amps x volts / 1000
2
kW = volts / (1000 x ohms)
2
kW = amps x ohms / 1000
Power factor
Power factor (pf) = Cos Ø = kW / kVA.
kW = kVA x pf
2
kVAr = kVA x (1-pf )
Three Phase Power
With three (3) phase power each line is 120 degrees out of phase with the next so different formula are required
kW = (1.732 x volts x amps x pf)/1000
amps = (kW x 1000) / (volts x pf x 1.732)
Three Phase Efficiency (Eff)
The formula below can be used to calculate the efficiency of a three phase motor (HP = Horsepower)
Eff = (HP x 746) / (volts x amps x pf x 1.732)
The above is only a selection of the more common formulas. These days most people rely on the internet via
computer or tablet for these calculations. A very good App is available for Android and Apple devices that make
these calculations easy:
“Electrical Engineering Pack” ….. from…… www.sparklesolutions.net
We at Viking Power Systems are not associated with this site but highly recommend their Electrical Engineering
software as we have used it ourselves !
Page 1