3 ph neutral current

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binney

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I posted this in response to another forum thread, but got no response.

The formula I used was
A^+B^+C^-(AB+BC+CA)=N CURRENT IN 3 PH

I?ve never calculated out the current on the Neutral in 3-ph before. I?ve always assumed if my circuits were close to being balanced and used for linear loads that I had no need to count the N as current carrying.

A B C N

10 10 10 0

10 10 0 10

6 15 9 63

10 10 2 64

16 16 0 256

16 16 2 196

16 16 14 4

Shut off a few switches, and the amps jump down on 1 phase and the N sky rockets.

Am I doing the math right??????????? I can?t be!!

What do harmonic loads do to the Neutral???
 
Re: 3 ph neutral current

You must take the square root of the final answer to your formula. Generally speaking, the neutral load won't be greater than the difference between any two phase loads.

Harmonic currents add on the neutral conductor on 4-wire wye-systems. This is stated throughout the code in FPN's.

[ March 13, 2005, 06:46 PM: Message edited by: bphgravity ]
 
Re: 3 ph neutral current

Harmonics add onto to current but how much, a significant amount or not?
 
Re: 3 ph neutral current

with certain types of "switching power supplies" it is my understanding that the "effective" value of "triplen" current in the neutral can be more than double the phase current and will also be at three times the frequency
 
Re: 3 ph neutral current

So one of your measurements was 16 Amps on A and B, 0 amps on C, and 256 amps on the Neutral??? Is that right??

That doesn't sound right. What is this and exactly what are these switches turning on or off?

Steve
 
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