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# Computing amps (220v 3 phase) from 250 amp, 400 v equipment

## Computing amps (220v 3 phase) from 250 amp, 400 v equipment

#1
11-14-14, 11:04 AM
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Join Date: Nov 2014
Location: usa
Posts: 1
Computing amps (220v 3 phase) from 250 amp, 400 v equipment

Hello, first time poster here. I have a quick question regarding converting from European voltage to US voltage.

The equipment is wired for 250 amp 400 volt service. I need to know how many amps that would pull after using a transformer to step it down to 220v 3 Phase.

If I use the general equation Watts = Volts X Amps I get 100,000 watts. If I plug that number into the equation using 220v I get 454.5 amps (100,000/220 = amps), which seems like far too much.

Is there a different equation for this conversion?

#2
11-14-14, 11:12 AM
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Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 16,321
Yes, there are different equations used with three-phase. I don't often work with three-phase so I have to look it up every time but it involves multipliers which include the following numbers. 1.41, 0.707 and 1.73 I honestly don't remember which you use or where you use it. It also depends upon the transformer connection you use.

One of the commercial electricians should be able to answer the question but it could be a few hours to even a couple of days for them to respond.

#3
11-14-14, 01:17 PM
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Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 9,785
So the scenario is you want to operate the equipment at 400V 3P from a 220V 3P (odd) service, using a transformer?

#4
11-14-14, 04:29 PM
Member
Join Date: Oct 2013
Posts: 511
What kind of equipment is this?
If it was designed to run at 400V, you may not be able to successfully use it at 220V.
And if you're talking 3 phase, you will likely be looking at running it at 208V.

#5
11-14-14, 04:43 PM
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Join Date: Mar 2006
Location: USA
Posts: 29,711
Sounds like European equipment. UK voltage 415VAC + 6% and - 10% and European is 380VAC +10% and -6%

#6
11-14-14, 07:13 PM
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Join Date: Jan 2010
Location: United States
Posts: 9,880
There are too many things to remember already so I don't worry about trying to remember formulas. I just use this site to select the formula I need.

Reliance - Formulas & Calculations

#7
11-14-14, 07:58 PM
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Join Date: Oct 2012
Location: Jersey
Posts: 65,415
Lots of useful formulas there.... thanks Joe.

#8
11-14-14, 08:25 PM
Member
Join Date: Oct 2013
Posts: 511
Joe,
I think the formula the OP is thinking of is for output voltage when wiring in delta and wye configurations.