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Math
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10-24-2007, 09:52 PM
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#1 |
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Member
Trade: Electrical
Join Date: May 2006
Location: so cal.
Posts: 58
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Math
I have a question if you have 36kva at 230 volts 3 phase what is the math formula to get the amperage per leg. I know it has 1.73 in it but can't for the life of me remember it. If you could help that would be great.
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10-24-2007, 09:54 PM
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#2 |
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Union Electrician
Trade: Inside Wireman
Join Date: Apr 2006
Location: Salt Lake City
Posts: 1,217
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Re: Math
36000/230*1.73
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10-24-2007, 09:57 PM
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#3 |
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Service & Repairs
Trade: Electrician
Join Date: Dec 2006
Location: Rahway, New Jersey
Posts: 3,998
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Re: Math
VA/ Volts x 1.73
36,000 VA divided by 230 volts x 1.73 Answer is 271 amps per leg.
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Electrician service in Rahway, Cranford, Clark, Westfield, Mountainside, Scotch Plains, Fanwood, Roselle, Roselle Park, and New Jersey | Same day electrical service and repairs | Licensed and Insured Electrician in Rahway Last edited by Magnettica; 10-24-2007 at 10:00 PM. |
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10-24-2007, 09:58 PM
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#4 |
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Electrical Contractor
Trade: Electrical
Join Date: Sep 2003
Location: NY State
Posts: 2,179
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Re: Math
Watts divided by volts divided by the square root of 3 (1.73).
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10-24-2007, 10:04 PM
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#5 |
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Member
Trade: Electrical
Join Date: May 2006
Location: so cal.
Posts: 58
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Re: Math
so 36000divided by 230 divided by 1.73 = 90 amps per leg correct?
wow thats alot of power for a cnc machine. |
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10-24-2007, 10:16 PM
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#6 |
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Electrical Contractor
Trade: Electrical
Join Date: Sep 2003
Location: NY State
Posts: 2,179
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Re: Math
Not for a big one.
 Another way is: watts / (voltsx1.73) as Joe and Mag wrote. Same result. 36000÷(230x1.73) 36000÷397=90.68 or 36000÷230÷1.73 156.52÷1.73=90.47
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10-24-2007, 10:21 PM
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#7 |
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Member
Trade: HVAC/R
Join Date: Oct 2007
Posts: 60
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Re: Math
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10-24-2007, 10:23 PM
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#8 | |
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Fentoozler
Trade: Professional Pie and Pastry Taster
Join Date: May 2007
Location: New Jersey
Posts: 5,585
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Re: MathQuote:
36,000/(1.73*230)=
36,000/398= 90.5A How are you arriving at 271 per? (90.5*3=271.5)
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10-24-2007, 10:23 PM
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#9 |
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Pro
Trade: Union Electrician
Join Date: Oct 2007
Location: Chicago
Posts: 135
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Re: Math
The answer is on pages 57 and 58 of your Ugly's book.
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10-24-2007, 10:41 PM
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#10 | |
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Service & Repairs
Trade: Electrician
Join Date: Dec 2006
Location: Rahway, New Jersey
Posts: 3,998
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Re: MathQuote:
I blanked up. I did 36kva/ 230 and took that sum and multiplied it by 1.73. I see where I went wrong. |
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10-25-2007, 09:59 PM
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#11 | |
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Old School Marine
Trade: Union Journeyman Electrician
Join Date: Sep 2007
Location: Ocean NJ
Posts: 374
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Re: MathQuote:
Hmmm, that would have made a big difference in the price of the wire......... |
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10-25-2007, 11:13 PM
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#12 |
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Union Electrician
Trade: Inside Wireman
Join Date: Apr 2006
Location: Salt Lake City
Posts: 1,217
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Re: Math
I believe that secondary windin configuration has something to do with the calc. (Wye or Delta).
Without vast knowledge I think Mag could also be right, given the configuration wasn't given in the question? Last edited by Sparky Joe; 10-25-2007 at 11:15 PM. |
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10-26-2007, 06:27 PM
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#13 |
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Service & Repairs
Trade: Electrician
Join Date: Dec 2006
Location: Rahway, New Jersey
Posts: 3,998
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Re: Math
Mistakenly, I gave total amperage of all 3 legs, not amps per leg.
270/ 3 = 90 |
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10-26-2007, 06:32 PM
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#14 | |
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Fentoozler
Trade: Professional Pie and Pastry Taster
Join Date: May 2007
Location: New Jersey
Posts: 5,585
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Re: MathQuote:
HUH? A 3Ø load with 90A per leg needs a 300A CB ('cause there is NO 270A CB)?
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10-26-2007, 06:42 PM
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#15 |
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Service & Repairs
Trade: Electrician
Join Date: Dec 2006
Location: Rahway, New Jersey
Posts: 3,998
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Re: Math
I thought we were talking about amperage per leg?
Yes, a 300A breaker would be correct protecting a 270 amp load. 240.4 (B) |
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10-26-2007, 06:50 PM
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#16 | ||
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Fentoozler
Trade: Professional Pie and Pastry Taster
Join Date: May 2007
Location: New Jersey
Posts: 5,585
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Re: MathQuote:
Quote:
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10-26-2007, 06:55 PM
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#17 |
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Service & Repairs
Trade: Electrician
Join Date: Dec 2006
Location: Rahway, New Jersey
Posts: 3,998
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Re: Math
Because at 90 amps per leg
a = 90 amps b= 90 amps c = 90 amps 90 + 90 + 90 = 270 Are u messing with me? |
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10-26-2007, 08:09 PM
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#18 | |||
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Fentoozler
Trade: Professional Pie and Pastry Taster
Join Date: May 2007
Location: New Jersey
Posts: 5,585
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Re: MathQuote:
I'm trying to figure out how we went from this... Quote:
Quote:
I realize you had a brain-fart on the math previously...but what's with the 270A ?
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10-26-2007, 09:05 PM
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#19 |
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Electrical Contractor
Trade: Electrical
Join Date: Sep 2003
Location: NY State
Posts: 2,179
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Re: Math
You guys are giving me a headache.
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10-27-2007, 01:29 AM
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#20 |
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Service & Repairs
Trade: Electrician
Join Date: Dec 2006
Location: Rahway, New Jersey
Posts: 3,998
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Re: Math
The 270 comes from 36kva divided by 230 times 1.73.
270 divided by 3 is 90. 270 is the result of a incorrect math figure that mathmatically works out to be the sum of all three legs. It's just something I picked up on after I realized where |
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