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Old 11-03-2011, 12:00 AM   #1
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Neutral Amps


Had this situation where a neutral splice had a total meltdown. Let's say the neutral for circ's. 1,3,5 (20A circuits - 3 phase). Circuit 1 - 15A, Circ. 3 - 12A, Circ. 5 - 13A. Obviously a poor connection right? I don't recall ever doing this but I amped out the neutral and it showed 30A (#12 wire). Technically, shouldn't that neutral conductor be a #10??? Did an overload cause this? All signs still point to the splice, but still?

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Old 11-03-2011, 05:35 AM   #2
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Neutral Amps


If this is a proper three phase supply,
Then the amps on the neutral should NOT be 30a,
The neutral currents should be sequential,
So should not be more than 15a.
At any one given moment.
If you have 30a, then you have other problems.

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Old 11-03-2011, 10:19 AM   #3
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Neutral Amps


Actually....if it was true 3ph...there would be no neutral....unless you have a 3 ph transformer that is giving you 3 individual 120Vac ckts.

I'm betting that it's actually just a standard house....2 120Vac feeds with a neutral.

If you do have a standard setup....using your setup above, cir 1 & 5 are on the same 120 and cir 3 is on the other (cir would be on this one as well). If you have a only a load on cir 1 & 3, assuming balanced (same amps), there is no current flow on the neutral. If cir 1 has 15A, cir 3 10A, then you would have 5A on the neut.

Back to your case....cir 1 is 15A & cir 5 is 13A for a total of 28A...with cir 3 at 12A, then you should only 16A on the neutral.....

This all assumes that you have a standard system and there are no other loads on any other circuits and that you are measureing the current at the neutral return back to the pole.

Can you draw a diagram of what you actually have?
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Old 11-03-2011, 11:00 AM   #4
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Neutral Amps


Quote:
Originally Posted by ddawg16 View Post
Can you draw a diagram of what you actually have?
Or post a picture of the load center with the cover off..
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Old 11-03-2011, 10:02 PM   #5
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Neutral Amps


It's a commercial panel. 3phase 4wire. Don't remember exact Amp draws on each circuit, but I do know the neutral amped out at 30. The 3 circuits are running cold cases at a deli.
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Old 11-03-2011, 10:04 PM   #6
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None of the circuits were overloaded, but pushing 80% on 20A breaker.
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Old 11-03-2011, 10:49 PM   #7
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Perhaps something additional to those 3 circuits is using that neutral?

Are the cold cases 3 phase or single phase?
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Old 11-03-2011, 11:49 PM   #8
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3 seperate 120v units. I think maybe a cash register is also tied in somewhere. Who knows what else.
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Old 11-04-2011, 12:26 AM   #9
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Cold cases? 1 breaker for each case. Something isn't right here. What is the voltageof the panel...and what is the voltage of the cases.
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Old 11-04-2011, 01:26 AM   #10
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Something is definitely not right. If all curcuits had about the same current the neutral would only have a couple amps. Are you sure two of those circuits aren't actually on the same phase?

That still wouldn't cause a catostophic failure. #12 shouldn't actually fail catostrophically until around 50 amps. I suspect it probably was a poor connection coupled with the overloaded neutral
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Old 11-04-2011, 01:31 PM   #11
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Neutral Amps


To settle this, you need to provide a picture of the electric panel with the cover off (as requested above).

And it would also be helpful to post pictures of the cold case "name plates". This says voltage, etc.

If you could post pictures of where that neutral goes, that would help to determine a solution.
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Old 11-04-2011, 07:27 PM   #12
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Can't get any photos. I was practically rushed to repair the problem as it was lunch time and the place was packed. I had to get the refrigerated foods back up and running. In hind sight, I wish I would've spent more time troubleshooting the cause, but it was a little difficult because there was so much going on at the time. I'm starting to think that maybe the high amperage was due to all three refers starting up at the same time, plus the lights in the cold cases.
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Old 11-04-2011, 09:54 PM   #13
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Quote:
Originally Posted by uconduit View Post
Can't get any photos. I was practically rushed to repair the problem as it was lunch time and the place was packed. I had to get the refrigerated foods back up and running. In hind sight, I wish I would've spent more time troubleshooting the cause, but it was a little difficult because there was so much going on at the time. I'm starting to think that maybe the high amperage was due to all three refers starting up at the same time, plus the lights in the cold cases.
It is impossible to for the nuetral to have a higher amperage than any of the hot wires if everything is as it should be. The nuetral only carries the unbalanced load. If all 3 phases had equal current, there would be nothing on the nuetral at all. If one had 12 one had 15 and one had 16 (or whatever you said) then neutral would only have a few amps on it. There is absolutely no reason the neutral would have 30 amps on it. Something is a wrong with their setup
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Old 11-05-2011, 10:59 AM   #14
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I'd trace out that neutral from the panel out to the load(S) it goes to. Open every J box. That neutral is being used for more than you think, or somewhere it is being used on two circuts of the same phase.

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