Shared neutral amperage-3 phase system

[Besoeker]

I do see it that way as you did not provide any solutions.

But it might have avoided an error.

I must be missing the obvious, how will this be done with live, in use circuits?

The check you suggested could be used on live circuits to eliminate wrong neutrals and leave the remaining possible correct ones. It might be tedious but at least it it would go some way, or even a long way, to determining what's what. But the circuits will be turned off at some point - see post #19. That could be the opportune time to check continuity.

In other words, what sounds good from the confines of an office is not always practical on the job.

I totally agree.

 

[kwired]

use of a circuit tracer to find what neutral goes with which ungrounded conductor(s) should work.

I assume these gambling machines are cord and plug connected. Just plug the tracer into a receptacle and back at the panel(s) you will have signal on both conductors supplying that receptacle. Identify it however you wish and move on to the next one.

You will also be able to verify any mistakes like one neutral common to more than three phase conductors or with two conductors on same phase without turning anything off and be able to make a plan to correct it.

It will take some time with the number of circuits but so will about any other method.

 

[bw9470]

That'll work. . . I used the ckt tracer to identify all the ckts before we moved them to the temp. panels in the first place. Didn't think about it havin the signal on the neutral also- The only problem i foresee with this is that the maintenance staff has tied some of the neutrals to ground in an effort to combat some neutral problems in the past (i guess that's the reason?) This place is a wreck!!!! Maybe you've done some casino work before?

 

[kwired]

That'll work. . . I used the ckt tracer to identify all the ckts before we moved them to the temp. panels. Didn't think about it havin the signal on the neutral also. You've done some casino work before?

Used circuit tracer before. Only casino work I have done is give them some of my money.

 

[dbuckley]

We re-fed some casino gaming ckts. with shared neutrals.

Is this for gaming machines? These are just computers, so are distinctly non-linear loads, so simple calculation is out.

Even branch circuits to gaming tables have non-linear loads on them these days.

 

[rattus]

Linear and unity power factor. Many loads are neither.

Bes, isn't it sufficient to just have equal PFs?

 

[Besoeker]

Bes, isn't it sufficient to just have equal PFs?

Not actually. Imagine three phases all with the same PF and equal currents. The formula would give In=0 and that would be fine for linear loads.
However, if you had third harmonic current in each of the three phase, this component is at three times the supply frequency. A complete cycle of this takes one third of the time for the fundamental which results in the third harmonic current from the three phases adding in the neutral rather than canceling.
I might have a picture which might make the explanation a bit clearer.
And it's the same story for for harmonics that are a multiple of three - sometimes referred to triple n

In other words, you could have balanced loads in the phases and an overloaded neutral conductor. It's not such an uncommon phenomenon. And will probably get worse as more and more non-linear loads come into use.

 

[rattus]

Not actually. Imagine three phases all with the same PF and equal currents. The formula would give In=0 and that would be fine for linear loads.
However, if you had third harmonic current in each of the three phase, this component is at three times the supply frequency. A complete cycle of this takes one third of the time for the fundamental which results in the third harmonic current from the three phases adding in the neutral rather than canceling.
I might have a picture which might make the explanation a bit clearer.
And it's the same story for for harmonics that are a multiple of three - sometimes referred to triple n

In other words, you could have balanced loads in the phases and an overloaded neutral conductor. It's not such an uncommon phenomenon. And will probably get worse as more and more non-linear loads come into use.

Sorry Bes, I did not clearly state the question. Of course the waveforms must be ideal, and the loads must be linear. I am just asking if the PFs must be unity. Seems to me it is sufficient that the PFs be equal--not necessarily unity.

 

[Besoeker]

Sorry Bes, I did not clearly state the question. Of course the waveforms must be ideal, and the loads must be linear. I am just asking if the PFs must be unity. Seems to me it is sufficient that the PFs be equal--not necessarily unity.

I agree.