electrical calculation of total current of 380v and 220v 3phase supply

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al6776bert@yahoo.com.ph Member Join Date: Jan 2009 Posts: 7	electrical calculation of total current of 380v and 220v 3phase supply 01/10/2009 1:55 PM
	Sir, i want to calculate the total load in current (ampere) for the following voltages supply. In our place we have two different types of voltage supply namely: 1) is the 3 phase 380v which has a line to neutral or ground voltage of 220v and a phase to phase voltages of 380v. and 2) is the 3 phase 220v which has a line to neutral of 110v and phase to phase of 220v. They told me that the formula of getting the total current in amp is I= total watts x power factor divided by square root of 3 x 220v.. my question is where did 220v came from.. and how do you apply this formula to what i said 3 phase 380v and 3 phase 220v power supply 60hz. please advise me with the correct formula or are there any formula in computing total current to get the main amp. (i.e main breaker supply of a load)
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wareagle Guru Join Date: Jun 2008 Location: Alabama Posts: 1610 Good Answers: 61	#1 Re: electrical calculation of total current of 380v and 220v 3phase supply 01/10/2009 4:08 PM
	The formula is amps = wattage/(1.73 x voltage). If the 380 volt and 220 volt are separate services, then determine the wattage for each voltage and substitute it into the formula. Total amps would be the addition of the two. If the 380 volt service feeds the 220 volt service via a transformer then just use the 380 volts in the formula to get the total amps.
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Anonymous Poster	#2 Re: electrical calculation of total current of 380v and 220v 3phase supply 01/11/2009 9:36 AM
	to calculate the current in amp there is only 2 cases : 1- in 3 phases system, voltage = 380V the power in Watt is P= (square root of 3)x380x(current in amp)x(power factor) 2- in Single phase, voltage = 220V the power in Watt is P= 220x(current in amp) so in the 2 conditions you can find the current in amp
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MuradRabei Member Join Date: Jan 2009 Location: Palestine Posts: 6	#3 Re: electrical calculation of total current of 380v and 220v 3phase supply 01/11/2009 5:27 PM
	The correct formula is: for 380/3Ph/60Hz and 220/3/60 P(3PH)=sqrt(3)IVPfEff where P: Power, I: Current, V: Voltage, Pf: power factor, Eff: Effeciency so I=P/(sqrt(3)VPfEff) for 220V/1Ph/60Hz which came from 380V line and Neutral and 110 or 120V/1Ph/60Hz which came from 220V line and Neutral P=IVPfEff so I=P/(VPfEff) in your case suppose Eff=1 Note I=I1+I2+....In sum of loads current in each circuit alone or Itotal=Ptotal/.....as above to select the Main Circuit Breaker use this formula below: MOCP=2.25*Imax+the other load Amps, Maximum Operating Current Protection you can choose MCB which is the next lower value of MOCP
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Anonymous Poster	#4 Re: electrical calculation of total current of 380v and 220v 3phase supply 01/12/2009 3:12 PM
	al6776bert; your 220 volt 3 phase with a neutral would have a 127 volt from neutral to any phase. perry
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