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Electrical Formula  

 

Contents


Ohms Law
Three Phase, Single Phase & DC Formula
Voltage Drop Formula
Maximum Circuit Length

Legend

R = Resistance, in ohms
P = Power, in watts
V = Voltage, in volts
I = Current, in amps
HP = Horsepower
L = Length
Eff = Efficiency e.g. 85% = 0.85
pF = Power Factor
Output kW = Net effective mechanical power of a motor

 

 

Ohms Law
  Power =     V2      or     R x I2     or     V x I 
R
  Voltage =     P      or     R x I     or   
I
  Resistance =     V      or     V2     or     P 
I P I2
  Current =     P      or     V     or   
V R

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Three Phase, Single Phase & DC Formula
Three Phase Single Phase Direct Current
kW = I x V x 1.732 x pF kW = I x V x pF kW = I x V
1000 1000 1000
kW = KVA x pF kW = KVA x pF
kW = HP x 746
1000 x Eff
Output
kW =		 I x V x 1.732 x pF x Eff Output
kW =		 I x V x pF x Eff Output
kW =		 I x V x Eff
1000 1000 1000
kVA = I x V x 1.732 kVA = I x V
1000 1000
kVA = kW
pF
I = kW x 1000 I = kW x 1000 I = kW x 1000
V x 1.732 x pF x Eff V x pF x Eff V x Eff
I = kVA X 1000 I = kVA X 1000
V x 1.732 V
I = HP x 746 I = HP x 746 I = HP x 746
V x 1.732 x pF x Eff V x pF x Eff V x Eff
HP = I x V x 1.732 x pF x Eff HP = I x V x pF x Eff HP = I x V x Eff
746 746 746
HP = kW x Eff x 1000
746
HP = kVA x Eff x 1000 x pF
746
pF = kW x 1000 pF = kW x 1000
I x V x 1.732 I x V
Eff = HP x 746 Eff = HP x 746 Eff = HP x 746
I x V x 1.732 x pF I x V x pF I x V

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Voltage Drop
Vc = 1000 x Vd or Vd = Vc x L x I where:   Vc = mV/Am
L = Length
I = Current
Vd = Voltage Drop
L x I 1000
  Australian Standards specify a maximum of 5% voltage drop across the entire circuit (including
  mains, submains and final subcircuit).

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Maximum Circuit Length Calculation
Lmax = where:   Tha = System Impedance Factor
Uo = Phase Voltage
Sph = Cable CSA
Spe = Cable Earth CSA
Resistivity = Resistivity for Copper
Ia = Magnetic release operating current,
     or fuse interupting capacity
Tha x Uo x Sph x Spe
Ia x Resistivity x (Sph+Spe)

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Disclaimer

Tecfind takes reasonable steps to ensure that this web site is kept up to date, but makes no warranties, representations or assurances, whether expressed or implied, as to the currency, reliability, accuracy or completeness of any information or data provided.
Author: Bill Wood 
Copyright © 2003 [Tecfind]. All rights reserved.