Neutral Cal.

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Flight987

Senior Member
If you pulled a multi-wire circuit from a 120/208 volt panelboard, consisting of circuit #2, circuit #4, and circuit
#6, and a grounded conductor, where there are 14A's on circuit #2, 15A's on circuit #4, and 7 A's on circuit
#6, how much current would be present on the Neutral?
I did the square root Neu. Cal.. What do I do when L squared # or larger than Lx numbers? To me it is a
simple Form. to work through. The answer is 7.55 I's No I didn't get it right, the answer is from the test key.
 
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david luchini

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Location
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Engineer
Did you use this formula: N=sqrt(A^2 + B^2 + C^2 - AB - AC - BC)?

This would provide an accurate answer if the power factor of each circuit current was the same. It would probably provide a good estimate where power factors are not the same on each circuit.

Plugging your values into that formula, I get 7.55 amps.




 

Flight987

Senior Member
No I

No I

No I didn't use that Fom. I used square root of L1Sq.+L2Sq.+L3Sq.- L1xL2xL3. I have not seen your Form.
in Mike's book's or by looking at Mike's fold out raceway chart. The question is word for word right from the
Prat. test.
 

Flight987

Senior Member
Did you

Did you

Did you recieve the last responce from ? Still learnig how to work this forum site. When I am finshed edt. a
message, what to click on to send it to you?
 

david luchini

Moderator
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Location
Connecticut
Occupation
Engineer
No I didn't use that Fom. I used square root of L1Sq.+L2Sq.+L3Sq.- L1xL2xL3. I have not seen your Form.
in Mike's book's or by looking at Mike's fold out raceway chart. The question is word for word right from the
Prat. test.

I don't know where your formula came from...it is not correct.

Try it as square root of L1Sq.+L2Sq+L3Sq-(L1xL2)-(L2xL3)-(L1xL3)
 

Flight987

Senior Member
I Is From

I Is From

It is from Mike Holt, Illustrated Guide to Electrical Formulas With Sample Calculations. I is the one he teaches
in the Exam. Prep. book. I can't type it very well. Page 183 Exam. Prep. book and page 116 in G T E F W S Cal.
I have used that one many times. It is the only one that he had in DVD's also.
 

david luchini

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Location
Connecticut
Occupation
Engineer
It is from Mike Holt, Illustrated Guide to Electrical Formulas With Sample Calculations. I is the one he teaches
in the Exam. Prep. book. I can't type it very well. Page 183 Exam. Prep. book and page 116 in G T E F W S Cal.
I have used that one many times. It is the only one that he had in DVD's also.

Sorry, don't have any of those books or DVDs.

I suspect you are transposing it wrongly.

Try square root of L1Sq.+L2Sq+L3Sq-(L1xL2+L2xL3+L1xL3)
 

Smart $

Esteemed Member
Location
Ohio
Sorry, don't have any of those books or DVDs.

I suspect you are transposing it wrongly.

Try square root of L1Sq.+L2Sq+L3Sq-(L1xL2+L2xL3+L1xL3)
Here's a version in algebraic equation format...

NeutralCurrentFormula.gif


...and I must reemphasize accuracy results only if the power factors (incl. leading or lagging) for all three line currents are identical. Otherwise, vector math or diagramming is required for any reasonable accuracy.
 

Flight987

Senior Member
God sent

God sent

It turned out to be a mistake on my part. Mike's Neu. Cal. work's fine. As he say's, slow down. But, it was a
God sent mistake. It lead me to here of the other Cal., that you talked about. I can't see that one now, but
can you help me on how to use this one. Kinda explain your smart's on why we need to use this otherone
at sometime. I didn't have algerbra in highschool, I am 49 year's young and math was allway's hard for me,
but I take my time and think hard and I get it done. Even table 220.55, I was supprised how well I did. Mike
say's the that table is almost impossible to teach. I don't give up trying. If I don't get it, I go over it, untill I
get it. 30 year's working in trade with Farther it would be nice if I could forget everything from past and just see
the new. No Dad has no clue, how the code apply's, and the math. He never had any math. Back to second
Form.. Could help with this? I am awally's willing to listen. That is back second formula that you showed me.
 
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Flight987

Senior Member
It seem that

It seem that

It seem's that it is the same Formula! The typer didn't put an x in the spot that it belong's. Instead there was a
dot or somthing put in there.
 

Smart $

Esteemed Member
Location
Ohio
It seem's that it is the same Formula! The typer didn't put an x in the spot that it belong's. Instead there was a
dot or somthing put in there.
Yes, it is the same formula. In algebraic notation, the multiplication operation is sometimes denoted with a dot rather than an ?. At other times when dealing with symbolic and letter constants or variables, multiplication operation notation is omitted.
a?b?c = a?b?c = abc​
 
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Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Here is a formula for a spreadsheet. Enter this formula in cell D5. Then enter Neutral currents in A5, B5 and C5

=SQRT(((A5*A5)+(B5*B5)+(C5*C5))-((A5*B5)+(B5*C5)+(A5*C5)))


If you like it is done here. Once the page opens go to file download and save as an excel spreadsheet. For some reason it does not work on line
 
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