# Finding line current when neutral current is given?



## 480sparky (Sep 20, 2007)

If you're given 3 out of the four variable (assuming it's a 3-ph wye system), it's just a 'math' question.










Ai=known & given
Ci=known & given
Ni=known & given

Solve for Bi.


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## Cletis (Aug 20, 2010)

*simple*

that's simple algebra that any master should be able to do without a calculator...


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## McClary’s Electrical (Feb 21, 2009)

√((Ia²+Ib²+Ib²)-(Ia*Ib)-(Ib*Ic)-(Ia*Ic))


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## CelticElect (Nov 17, 2011)

*Transpose*



480sparky said:


> If you're given 3 out of the four variable (assuming it's a 3-ph wye system), it's just a 'math' question.
> 
> 
> 
> ...


Right, I know the formula. I need to know to transpose it. Oh, Cletis we could use your help here too, since you are so smart and any master can do it.


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## brian john (Mar 11, 2007)

Cletis said:


> that's simple algebra that any master should be able to do without a calculator...


 
Please by all means lay it out for us.

A=20
B=?
C=19
N=13.5


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## Cletis (Aug 20, 2010)

*Geez*

I'm just saying it's algebra 1/2. That's 7th grade manipulations

Just sq. the right and left sides for now. I'll solve when I get back...


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## CelticElect (Nov 17, 2011)

Cletis said:


> I'm just saying it's algebra 1/2. That's 7th grade manipulations
> 
> Just sq. the right and left sides for now. I'll solve when I get back...


Cletis

That is how you get rid of the square root. The rest is in the dark with me. If you and another math magician can figure it out, more power to ya.


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## Cletis (Aug 20, 2010)

*problem*

It wouldn't be any fun to go right to answer. 

How about we all work it out to brush up on our math skills. Here to start. I'm outta here. Check back in later

Order of solving an algebra problem.

Parentheses and Brackets -- Simplify the inside of parentheses and brackets before you deal with the exponent (if any) of the set of parentheses or remove the parentheses.

Exponents -- Simplify the exponent of a number or of a set of parentheses before you multiply, divide, add, or subtract it.

Multiplication and Division -- Simplify multiplication and division in the order that they appear from left to right.

Addition and Subtraction -- Simplify addition and subtraction in the order that they appear from left to right.


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## 480sparky (Sep 20, 2007)

Cletis said:


> It wouldn't be any fun to go right to answer.
> 
> How about we all work it out to brush up on our math skills. Here to start. I'm outta here. Check back in later
> 
> ...


Well, duh







...... that's the _Order of Operations_.

Now tell us how to *Transpose the formula* so it reads Bi=___________________.


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## Cletis (Aug 20, 2010)

*Transpose*

you are right. 

Here is one basic example of transposing which can be applied to line voltage problem.


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## 480sparky (Sep 20, 2007)

Cletis said:


> you are right.
> 
> Here is one basic example of transposing which can be applied to line voltage problem.



Googling your way to wisdom? :laughing:


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## Cletis (Aug 20, 2010)

480sparky said:


> Googling your way to wisdom? :laughing:


Sort of. Trying to find simple problems to show how to solve bigger problems for those that are weak in the algebra area.


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## troublemaker1701 (Aug 11, 2011)

480sparky said:


> Well, duh
> 
> 
> 
> ...


It is not that simple B=? is the last step of the problem


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## Cletis (Aug 20, 2010)

*ok*

Ok. Here are some wild and crazy guess's

B = 

a. 4.6

b. 2.3

c. 0 

d. 10.4

e. none of the above 

??


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## RePhase277 (Feb 5, 2008)

It isn't that simple to solve for B since it will be on both sides of the equation in multiple terms after squaring to get rid of the radical. I haven't worked the problem, but I suspect it will take multiple rearrangements and may be a quadratic solution as well.


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## troublemaker1701 (Aug 11, 2011)

The first step is to reverse equation 
13.5=sqrt(20^(2)+B^(2)+19^(2)-20xB-20x19-Bx19
sqrt(20^(2)+B^(2)+19^(2)-20xB-20x19-Bx19=13.5
second step is to remove sqrt by squaring of equation
(20^(2)+B^(2)+19^(2)-20xB-20x19-Bx19=13.5^(2)
third simplify right side
(20^(2)+B^(2)+19^(2)-20xB-20x19-Bx19=182.25
4th simplify left side
(20^(2)+B^(2)+19^(2)-39B-380=182.25
400+B^(2)+361-39B-380=182.25
761+B^(2)-39B-380=182.25
381+B^(2)-39B=182.25
5 zero out right side by subtracting 182.25 from both sides
198.75+B^(2)-39B=0
subtract 198.75 from both sides
B^(2)-39B= -198
I got the hard part done


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## troublemaker1701 (Aug 11, 2011)

NOT REALLY now the hard stuff starts


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## Cletis (Aug 20, 2010)

*solve*

Now you just have to solve by factoring


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## troublemaker1701 (Aug 11, 2011)

Cletis said:


> Now you just have to solve by factoring


OK show me


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## Cletis (Aug 20, 2010)

*like this*

kinda like this 

Solve x2 – 5x = 0.
This two-term quadratic is easier to factor than were the previous quadratics: I can factor an x out of both terms, taking the x out front. (Warning: Do not "divide the x off", do not make it magically "disappear", or you'll lose one of your solutions!)

x(x – 5) = 0 
x = 0 or x – 5 = 0 
x = 0 or x = 5

Then the solution to x2 – 5x = 0 is x = 0, 5


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## Cletis (Aug 20, 2010)

*oops*

x^2 + 5x = 0


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## 480sparky (Sep 20, 2007)

troublemaker1701 said:


> It is not that simple B=? is the last step of the problem


That's what I'm asking for.... the steps to get there with.


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## Cletis (Aug 20, 2010)

*try*

try 

B^(2)-39B= -198 now for x^2 + 5x = 0 with those other steps as examples

so 

b(b x -39) = -198

I think...i've been drinking last few hours so...:drink:


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## troublemaker1701 (Aug 11, 2011)

480sparky said:


> That's what I'm asking for.... the steps to get there with.


Look at 17


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## Cletis (Aug 20, 2010)

*Dang*

Dang, we are real close. I think I screwed up but I know we are close. I may have to wait til alcohol wears off tomorrow to retackle this? 

Folow this one 

x2 + 5x + 6 = 0

so substute

B^2 -39B + 198 = 0 then solve (factor) this maybe


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## troublemaker1701 (Aug 11, 2011)

I am going to bed 9 am comes around pretty quick


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## Cletis (Aug 20, 2010)

*few more*

i'm gonna have a few more beers. I'll probably hit this tomorrow night but I think it's almost done. Just factoring and foil method I think


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## Cletis (Aug 20, 2010)

*got*

this is what I got in fractional form 

{ 39 ± Sq Root ( 1.5210e+3 - 792 ) } / 2


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## Cletis (Aug 20, 2010)

*6 and 33*

ok. got 6 and 33 

B^2 -39B + 198 

Using 6

36 - 234 + 198 = 0

using 33 

1089 - 1287 +198 = 0


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## 480sparky (Sep 20, 2007)

troublemaker1701 said:


> Look at 17



From Cletis. :whistling2:


BTW, to answer Brian's set of variables, it's 32.972


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## frenchelectrican (Mar 15, 2007)

brian john said:


> Please by all means lay it out for us.
> 
> A=20
> B=?
> ...


For Delta connected or Wye connection for the B question ??

I will post the answer in the moment.

Merci,
Marc


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## don_resqcapt19 (Jul 18, 2010)

You could always cheat and use the "guess and check" method with an spreadsheet neutral current calculator. You put the A and C currents in and they try values of B until you get 13.5 amps of neutral current. Yes I know that you don't learn how to do the math that way, but you can quickly get the correct answer.


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## brian john (Mar 11, 2007)

don_resqcapt19 said:


> You could always cheat and use the "guess and check" method with an spreadsheet neutral current calculator. You put the A and C currents in and they try values of B until you get 13.5 amps of neutral current. Yes I know that you don't learn how to do the math that way, but you can quickly get the correct answer.


I limped through high school Algebra that way


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## Cletis (Aug 20, 2010)

*ok*



480sparky said:


> From Cletis. :whistling2:
> 
> 
> BTW, to answer Brian's set of variables, it's 32.972


ok. That makes sense then. I had it down to 33 or 6 for solutions last night. That was sort of fun in a sick way working on ol quadratic equations. I need to figure out how to get 33 now instead of 6 as other option and were done I think. The rest of all this thread is good I think for the algebra....


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## Cletis (Aug 20, 2010)

*Btw*



brian john said:


> Please by all means lay it out for us.
> 
> A=20
> B=?
> ...


Oh, BTW. I was being "Highly Sarcastic". The "Your a Master you should know the answer to that" or "Any Master should know answer to that" seems to be the ongoing jab at anyone who asks anything about anything on here. I was poking fun. I was around teachers for years in a really hard subject and if someone ever laughed or ridiculed someone who asked a question no matter how stupid it seemed you would get a big scolding. This was EE, Physics, etc.. type material so......There are too many things to know in this business to know even close to everything and we really should back off making fun of people that ask questions that may seem simple to yourself. We need a sarcastic smiley on here or something. 

But, that was 7th or 8th grade quadratic equations still. I actually had somewhat of a time with it. I knew it very well in 7th grade AP but it has been like 40 yrs of non-use so I'm glad I brushed up on this thread.


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## 480sparky (Sep 20, 2007)

Cletis said:


> ok. That makes sense then. I had it down to 33 or 6 for solutions last night. That was sort of fun in a sick way working on ol quadratic equations. I need to figure out how to get 33 now instead of 6 as other option and were done I think. The rest of all this thread is good I think for the algebra....


I just punch the equation into my HP 48G+ and enter the variables into the Solver. :whistling2:


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## troublemaker1701 (Aug 11, 2011)

480sparky said:


> I just punch the equation into my HP 48G+ and enter the variables into the Solver. :whistling2:


Dang that is where I messed up I did it on paper.
:whistling2:


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## troublemaker1701 (Aug 11, 2011)

B=6.03
sqrt(20^(2)+B^(2)+19^(2)-20xB-20x19-Bx19=13.5
sqrt(20^(2)+6.03^(2)+19^(2)-20x6.03-20x19-6.03x19=13.5
sqrt(400+36.36+361-120.6-380-114.57=
sqrt(797.36-614.63)=
sqrt(182.73)=13.52


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## don_resqcapt19 (Jul 18, 2010)

B=32.98
sqrt(20^(2)+B^(2)+19^(2)-20xB-20x19-Bx19=13.5
sqrt(20^(2)+32.98^(2)+19^(2)-20x32.98-20x19-32.98x19=13.5
sqrt(400+1087.68+361-659.6-380-626.62=
sqrt(1848.68-1666.22)=
sqrt(182.46)=13.51


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## troublemaker1701 (Aug 11, 2011)

don_resqcapt19 said:


> B=32.98
> sqrt(20^(2)+B^(2)+19^(2)-20xB-20x19-Bx19=13.5
> sqrt(20^(2)+32.98^(2)+19^(2)-20x32.98-20x19-32.98x19=13.5
> sqrt(400+1087.68+361-659.6-380-626.62=
> ...


WOW is not math strange 2 right answers :blink::laughing:


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## 480sparky (Sep 20, 2007)

On paper, I came up with the 32.972.

My 48G+ comes up with 6.02780641469.


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## Cletis (Aug 20, 2010)

So... 6 and 33 were correct.


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## 480sparky (Sep 20, 2007)

Now I can't get the 32.972. I think we both made the same long-hand mistake somewhere. If I enter that and solve for N, it comes back as 14.59.


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## troublemaker1701 (Aug 11, 2011)

480sparky I like that calculator sure beats long hand
When I took my Masters you could only use a basic calculator.
But I don't remember a problem that complex on the exam.
I might be wrong its been 19 years since I took Masters.


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## 480sparky (Sep 20, 2007)

troublemaker1701 said:


> 480sparky I like that calculator sure beats long hand
> When I took my Masters you could only use a basic calculator.
> But I don't remember a problem that complex on the exam.
> I might be wrong its been 19 years since I took Masters.


I was able to use this calculator on my last test, but I never needed anything with this kind of firepower. I just used the basic 4-5 functions. I had an old TI 38 in my coat pocket, in case they refused to let me use this one, but they did.


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## Bulldog1 (Oct 21, 2011)

480sparky said:


> I was able to use this calculator on my last test, but I never needed anything with this kind of firepower. I just used the basic 4-5 functions. I had an old TI 38 in my coat pocket, in case they refused to let me use this one, but they did.



We aren't allowed to bring our own in the testing center. They provide it and a dry erase board, code book and fire alarm book.


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## brian john (Mar 11, 2007)

In my original quotation I used B=6.


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## brian john (Mar 11, 2007)

480sparky said:


> Now I can't get the 32.972. I think we both made the same long-hand mistake somewhere. If I enter that and solve for N, it comes back as 14.59.


You could do radio/TV voice over work.:thumbup:


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## 480sparky (Sep 20, 2007)

brian john said:


> You could do radio/TV voice over work.:thumbup:



I need to.......uh,........ 'eliminate' James Earl Jones first.


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## RePhase277 (Feb 5, 2008)

Is it surprising to have two right answers? Quadratics always do.


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## don_resqcapt19 (Jul 18, 2010)

480sparky said:


> Now I can't get the 32.972. I think we both made the same long-hand mistake somewhere. If I enter that and solve for N, it comes back as 14.59.


It works as a correct answer. See post #40.


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## troublemaker1701 (Aug 11, 2011)

best way to find load is use a amprobe and put away pencil and paper


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## brian john (Mar 11, 2007)

troublemaker1701 said:


> best way to find load is use a amprobe and put away pencil and paper


 
Sissy......:no:

Sometimes that is not feasible, such as with a switchboard with phase metering.


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## 480sparky (Sep 20, 2007)

troublemaker1701 said:


> best way to find load is use a amprobe and put away pencil and paper



So you have the ability to load a 3-ph panel to those numbers?


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## troublemaker1701 (Aug 11, 2011)

dang it I was just joking


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## brian john (Mar 11, 2007)

troublemaker1701 said:


> dang it I was just joking


We know but below a 100 post we get to pick on you.:no::no::whistling2:


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