neutral amp vs panel amp

[hairsh.k]

Hi, I am an engg. student. In just saw a panel board having different bus bar for main and neutral bus bar. Is it possible and why? Nameplate Tag says
AMP: 30
NEUT AMP: 100
VOLTS : 208Y/120, 3P,4W

 

[LarryFine]

Welcome to the forum.

Please explain what you mean by " different bus bar for main and neutral bus bar."

What is the "main" bar?

 

[hairsh.k]

please follow this link and download the image, that was type above
AMP: 30
NEUT AMP: 100
VOLTS : 208Y/120, 3P,4W
these are the rating.my question is it possible, neutral amp and main amp can be different in same panelboard and how. generally neutral amp and main amp are same. let me know if you need more info.

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[ptonsparky]

That's certainly what it says. Any chance you have the complete label ?

 

[hairsh.k]

check this link : https://www.dropbox.com/s/sc33k7mmo8mw796/IMG_1987.jpg?dl=0
this is all I have, is possible? any documents how for this of link.

 

[LarryFine]

My first guess is it's a mis-print, and should say "300 amps."

 

[hairsh.k]

My first guess is it's a mis-print, and should say "300 amps."

but is it possible that we can use different rating bus bar for main and neutral in same panel board.

 

[LarryFine]

but is it possible that we can use different rating bus bar for main and neutral in same panel board.

It is. But, in 3-phase panels, the neutral current is normally a fraction of the line currents.

Why would a panel have such a low rating? And, why with a much heavier neutral bus?

 

[hairsh.k]

It is. But, in 3-phase panels, the neutral current is normally a fraction of the line currents.

Why would a panel have such a low rating? And, why with a much heavier neutral bus?

I thought it was typo but again I saw another name plate having 20A main and 100A neutral at 480Y/277. I can't find the answers on internet that is why I came here for expert's opinion. thanks for your reply.

 

[hairsh.k]

please see another panel image having different panel amp. and neutral amp.

 

[Carultch]

Hi, I am an engg. student. In just saw a panel board having different bus bar for main and neutral bus bar. Is it possible and why? Nameplate Tag says
AMP: 30
NEUT AMP: 100
VOLTS : 208Y/120, 3P,4W

For linear loads, where voltage and frequency are in direct proportion, and both are close enough to be modeled as simple sine waves, it is OK to use a neutral that is the same amp rating as the panel itself.

For harmonic-intensive loads, it becomes important to anticipate neutral current that is greater than the current on any phase. This has to do particularly with harmonics that are multiples of 3 for three-phase, because these add up, rather than cancel, on the neutral and conductor. Or even harmonics, for 120/240V split phase, would have the same effect.

What harmonic means, has to do with the wave shape of the waveform of current not being a perfect sine wave. As an engineer, you've probably learned about the Fourier series, which is a concept of how other shapes of waveforms (square waves, triangle waves, sawtooth waves, etc) can be expressed a summation of sine waves. There is the fundamental waveform at the lowest frequency, which produces the general pattern to the wave shape and repeat pattern. Then, in addition to that, there are higher frequencies at ratios from the fundamental frequency, which distort the wave shape from a perfect sine wave, to the shape it really is. Given a 60 Hz grid frequency, it is the 180 Hz harmonics that have this problem on three phase systems. And to a lesser extent, any multiple of 180 Hz.

 

[LarryFine]

But a panel this large with only a 20- or 30-amp main?

 

[Carultch]

But a panel this large with only a 20- or 30-amp main?

Another possibility is that there are fewer standard size neutral busbar ratings. Such that any panel 100A and less, would have a 100A neutral, due to the lack of availability of smaller busbars.