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#127800 - 01/04/02 05:44 AM Voltage drop calculation
cinkerf Offline
Member

Registered: 12/03/00
Posts: 81
Loc: Pittsburgh, Pennsysvania. ...
In today's code question of day http://www.ecmag.com/cqd/index.cfm?ID=20020104 two methods for performing voltage drop calculations were given for an A.C. circuit. Is one method better than other? Is one method more popular than the other?

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#127801 - 01/04/02 05:57 AM Re: Voltage drop calculation
Bill Addiss Offline
Member

Registered: 10/07/00
Posts: 4196
Loc: NY, USA
Frank,

I've always tried to use formulas that are simple (for me) to remember. In this case Ohm's Law; (I = E/R)

E = I x R where E is the Voltage

Bill

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#127802 - 01/04/02 07:18 AM Re: Voltage drop calculation
Frank Cinker Offline
Member

Registered: 07/29/01
Posts: 317
Loc: Pennsylvania
Thanks Bill. By the way, Happy New Year....

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#127803 - 01/04/02 07:21 AM Re: Voltage drop calculation
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: WI, USA
For short distances (less than 150 ft), I use simple formulas. I like the Square D Motor Data Calculator voltage drop feature.

For longer distances I like to consider the impedance of the system rather than only the resistance. This means worrying about the raceway, Power Factor, and phase configuration. I use the tables in the Ferraz-Shawmut Book of Electrical Information.

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#127804 - 01/04/02 10:09 AM Re: Voltage drop calculation
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
I just found this site with some downloadable elecrical software. It has a series voltage drop calculator for multiple loads on long runs. It is free and I downloaded it this morning. Looks like it will work nice, but I haven't really played with it yet. http://www.edreference.com/default.asp
Don(resqcapt19)
_________________________
Don(resqcapt19)

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#127805 - 01/04/02 02:16 PM Re: Voltage drop calculation
Frank Cinker Offline
Member

Registered: 07/29/01
Posts: 317
Loc: Pennsylvania
Over the years I've take several certification examinations. Only small calculators were permitted to be used. I've had luck using the following calculation for voltage drop for single phase circuits: VD=2KLI/CM. x.866 if three phase circuit. For these particular exam questions power factor, raceway etc were not a factor. I was thankful for that...

For those of you who took exams, what formula did you use?

[This message has been edited by Frank Cinker (edited 01-06-2002).]

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#127806 - 01/09/02 03:49 AM Re: Voltage drop calculation
George Corron Offline
Member

Registered: 05/16/01
Posts: 728
Loc: Lorton, Va USA
Guys,
Ugly's has always been the standard around here. Don, Uglys was issued to me by the IBEW in my apprenticeship, since we came through about the same time didn't you use it ? If they quit publishing Uglys I've always said I'm leaving the trade. It is also the standard used locally for most every test.

Single phase, 2 wire = 2K X L X I / Cm

3 phase, 3 wire = 1.73K X L X I/ Cm

K = 12.9 for copper, 21.2 for aluminum
L = length, I = amps, and Cm = Circular mil area from Chap 9, Table 8

The only thing you have to check occasionally is the "K" rating, that has moved around since I came in the trade because the cma table was revised.

I've been around long enough that #10 wire was 10,000 cm, it has been revised to 10,380, but the formula has pretty much remained the same.

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#127807 - 01/10/02 07:33 PM Re: Voltage drop calculation
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
George,
They didn't give us "Ulglys", but those are the formulas that we were taught.
Don
_________________________
Don(resqcapt19)

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#127808 - 01/10/02 11:41 PM Re: Voltage drop calculation
Elzappr Offline
Member

Registered: 12/20/01
Posts: 273
Loc: Oregon
The K factor has changed through the years because the Ohms per 1000ft figure in Table 8 of Ch 9 depends on the assumed temperature. In the '87 code they stopped assuming 25C and started assuming 75C.
K is just shorthand for: (dc resistance value) X (circular mil area) divided by 1000.
You have to watch out for the assumed temperature if you are going to use the formula with a K factor...not to be confused with K factors of transformers!

[This message has been edited by Elzappr (edited 01-11-2002).]

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#127809 - 01/11/02 08:48 PM Re: Voltage drop calculation
sparky66wv Offline
Member

Registered: 11/17/00
Posts: 2339
Loc: West Virginia
I would not have passed my journeyman's without an UGLY's... Is the 2002 out yet?
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