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Old 03-01-2015, 04:32 PM   #1
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Default Math doesn't work on this panel

Last week at work I was given a job to add switches to the lights in a large open area in a building so they didn't have to use the breakers anymore. Instead of twelve switches I was going to use a lighting contactor and consolidate circuits because they had removed several lights and converted to t8 from t12. All the lights and wiring are mostly from the 50s/60s in a concrete ww2 5story building.



Didn't look like a bad job to begin with. A few 30 amp breakers on 12 gauge wire but no biggie. Got to looking at the wire and found a few mwbcs so I went to sort those out. I found that there were to few of neutrals on some of the circuits and some mwbcs were on the same phase. While I was finding what neutrals went where I ran into a big problem. I have 4 circuits with two neutrals that have a big problem; three of the circuits share one neutral, twocircuits share one neutral and one of the four circuits share both neutrals. Each circuit operates fine on its own and all the currents add up on their respective and shared neutrals like they should. The ballasts are ge multi volt ballasts so that explains why the lights all operate perfectly but the math still doesn't work. There is also several neutrals grounded out in the wiring making all of the conduits carry current.

Then I found on the outlets in the area there are 3 circuits sharing a neutral. I put a 9.8 amp load on one circuit and had 9.8 returning on the grounded conductor. I put a 2 amp load on another's circuit on the other phase and had 2 amps returning on the grounded conductor. I turn on both and I get 9.6 amps on the grounded conductor. I move the circuits to the same phase and turn on the loads and get 10 amps on the grounded conductor. Math isn't working here. I added a 5 amp load to the third circuit and it does the same thing.

After seeing the work that the electricians used to do here it doesn't suprize me that it is all messed up but the fact that the math isn't working is confusing me. I can't figure out what to go look for. I will just have to open everything up.



Also what are these qo breakers with the odd clip. These are all 30s.


Most of the breakers are so old they don't have the trip indicator or the size cast in the handle. One even says Cedar Rapids iowa instead of Detroit.
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Old 03-01-2015, 07:21 PM   #2
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sounds like fun, git'r done !

divide and conquer. sounds like it's gonna be one ckt at a time. Hopefully you are getting paid to do some new pipe and rewiring, sounds like you need it.
talk em into a panel upgrade and put some of the cost in there.
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Old 03-01-2015, 08:04 PM   #3
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Have you considered phase cancelation ?
Differences in phase on the different circuits
could be having a phase cancelation effect.
cancelling some of the current on the return line.

Don't over think these things
use your instruments and measure things
if the instruments say fine
And there's no obvious distress
Then don't worry too much.
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Old 03-01-2015, 08:29 PM   #4
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Quote:
Originally Posted by Jhellwig View Post
Last week at work I was given a job to add switches to the lights in a large open area in a building so they didn't have to use the breakers anymore. Instead of twelve switches I was going to use a lighting contactor and consolidate circuits because they had removed several lights and converted to t8 from t12. All the lights and wiring are mostly from the 50s/60s in a concrete ww2 5story building.



Didn't look like a bad job to begin with. A few 30 amp breakers on 12 gauge wire but no biggie. Got to looking at the wire and found a few mwbcs so I went to sort those out. I found that there were to few of neutrals on some of the circuits and some mwbcs were on the same phase. While I was finding what neutrals went where I ran into a big problem. I have 4 circuits with two neutrals that have a big problem; three of the circuits share one neutral, twocircuits share one neutral and one of the four circuits share both neutrals. Each circuit operates fine on its own and all the currents add up on their respective and shared neutrals like they should. The ballasts are ge multi volt ballasts so that explains why the lights all operate perfectly but the math still doesn't work. There is also several neutrals grounded out in the wiring making all of the conduits carry current.

Then I found on the outlets in the area there are 3 circuits sharing a neutral. I put a 9.8 amp load on one circuit and had 9.8 returning on the grounded conductor. I put a 2 amp load on another's circuit on the other phase and had 2 amps returning on the grounded conductor. I turn on both and I get 9.6 amps on the grounded conductor. I move the circuits to the same phase and turn on the loads and get 10 amps on the grounded conductor. Math isn't working here. I added a 5 amp load to the third circuit and it does the same thing.

After seeing the work that the electricians used to do here it doesn't suprize me that it is all messed up but the fact that the math isn't working is confusing me. I can't figure out what to go look for. I will just have to open everything up.



Also what are these qo breakers with the odd clip. These are all 30s.


Most of the breakers are so old they don't have the trip indicator or the size cast in the handle. One even says Cedar Rapids iowa instead of Detroit.
I hope those were #10's under those 30's
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Old 03-01-2015, 09:05 PM   #5
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If the pipes are returning current, you might as well quit measuring and worry about it when a neutral burns up.
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Old 03-01-2015, 09:54 PM   #6
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Originally Posted by wildleg View Post
sounds like fun, git'r done !

divide and conquer. sounds like it's gonna be one ckt at a time. Hopefully you are getting paid to do some new pipe and rewiring, sounds like you need it.
talk em into a panel upgrade and put some of the cost in there.
I am a maintinence electrician for the company so I could work on this for the next three months if I wanted to.
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Old 03-01-2015, 09:57 PM   #7
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Originally Posted by dmxtothemax View Post
Have you considered phase cancelation ?
Differences in phase on the different circuits
could be having a phase cancelation effect.
cancelling some of the current on the return line.

Don't over think these things
use your instruments and measure things
if the instruments say fine
And there's no obvious distress
Then don't worry too much.
The phase cancelation is what isn't adding up. I spent the last two days with my meter trying to figure this out.
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Old 03-01-2015, 09:59 PM   #8
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Originally Posted by Black Dog View Post
I hope those were #10's under those 30's
Nope. #12 tw. Good thing there are ground loops to take some of the load off the neutrals.

It is in a training center that doesn't get used very often.
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Old 03-01-2015, 10:14 PM   #9
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Originally Posted by mcclary's electrical View Post
If the pipes are returning current, you might as well quit measuring and worry about it when a neutral burns up.
.........right.....



My favorite thing was the run of half inch emt with two #12 twos in it that had two offsets, a ninety, 3 3bend saddles and two 4 bend saddles. I barley managed to get the tw out and barley got 3 #12 thhn and 5 #14 thhn's back in it.
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Old 03-01-2015, 11:11 PM   #10
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If the current is other than unity power factor or harmonic typical equations wont work.

This may help post 33:

http://forums.mikeholt.com/showthrea...=167171&page=4
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Old 03-02-2015, 12:28 PM   #11
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The T8 F32 are going the way of the 100 watt light bulb.
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Old 03-02-2015, 12:50 PM   #12
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^OK.........that doesn't affect math.....


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If the current is other than unity power factor or harmonic typical equations wont work.

This may help post 33:

http://forums.mikeholt.com/showthrea...=167171&page=4
It is a single phase panel and my load on the outlets was a vacume and a band saw. I have a true RMS meter so power factor and harmonics aren't the problem.
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Old 03-02-2015, 02:23 PM   #13
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I am curious about those breakers also.
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Old 03-02-2015, 03:11 PM   #14
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The phase cancelation is what isn't adding up. I spent the last two days with my meter trying to figure this out.
And IMHO you have already found the reason why:

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...... There is also several neutrals grounded out in the wiring making all of the conduits carry current....... AND: ....... Good thing there are ground loops to take some of the load off the neutrals.

Fix those issues and I'll bet things will equal out again. (And you'll uncover some overloaded neutrals.....)

On that thought..I'm also willing to bet that the reason you have neutrals grounded out to the conduits is that they WERE overloaded and burned up in the conduits, creating those unintentional bonds.
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Old 03-02-2015, 06:11 PM   #15
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If you are a maintenance guy that can take your time, I'd start on this project one conduit at a time. Trace all the wires out, repull extra neutrals if you need them, add a j-box or two if over 360 degrees, etc. You'll get it sorted out and working 100%, it'll just take a little time.

It's obvious that the electricians before you NEVER took any time to do it properly, so here's your chance.
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Old 03-03-2015, 12:24 PM   #16
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DO NOT SHARE A NEUTRAL START OVER. Sharing a neutral is a bad practice to get into it will get you or someone down the line hurt.
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Old 03-03-2015, 01:12 PM   #17
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DO NOT SHARE A NEUTRAL START OVER. Sharing a neutral is a bad practice to get into it will get you or someone down the line hurt.
Haha, right. How is it going to hurt someone if installed properly?
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Old 03-03-2015, 01:53 PM   #18
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DO NOT SHARE A NEUTRAL START OVER. Sharing a neutral is a bad practice to get into it will get you or someone down the line hurt.
Some on here who know me well would be surprised to see me disagreeing with you on this, but it is true.

Shared neutrals are perfectly safe, Code Compliant in most cases, and save considerable amounts of wire, especially in the OP's case.

The only ones who will get hurt "down the line" are incompetents who have no business working on electrical equipment.

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Haha, right. How is it going to hurt someone if installed properly?
It won't of course.


Now, all that said, in the OP's case since the lighting is most likely electronic ballasts, I would try, if possible, to run dedicated neutrals IF the likelihood of harmonic issues exists.

But from his descriptions the conduits are already jammed full so probably can't be done. In that case, properly phased MWBC's will work well.
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Old 03-03-2015, 02:27 PM   #19
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DO NOT SHARE A NEUTRAL START OVER. Sharing a neutral is a bad practice to get into it will get you or someone down the line hurt.
The only time it is bad to share a neutral is if you are to dumb to install a wirenut properly.



If I could quit getting called off this job I could be done by now. I opened up some boxes and see no evidence of any wires being overloaded. I am thinking that maybe someone wired a ballast wrong when they converted to t8 or the lighting track got something stuck in it when they dry ice blasted and winter the area.
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Old 03-03-2015, 02:57 PM   #20
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The disagreement we have is just that but it also showe's the type of work you do meaning " not commerical". Where and how I work if you did that you would have your check the next day. 277 480 volt lighting will teach you not to do it. And always the spec on any job I have ever worked on. Try it with a three wire and two plugs lift the n and see what happens
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