Okay i'm trying to figure out how to calculate a neutral load by using clamp to determine the amperage on the three phases and then calculate what the amperage on the shared neutral should be. . . for example- a=4.4A, b=3.6A, c=5.2A Should my neutral load be the sum of these?
Shared neutral amperage-3 phase system
- Thread starter bw9470
- Start date
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Here is the formula for 3 phase
- Location
- Massachusetts
Here is the formula for 3 phase
That is how I was shown in trade school and how I would do it now but there are other ways. I also think the above formula is only accurate if all the loads are linear.
Linear and unity power factor. Many loads are neither.I also think the above formula is only accurate if all the loads are linear.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
You can put your clamp around the neutral wire-- No???
- Location
- Massachusetts
Yeah- I can clamp the neutral wire.
kda3310
Senior Member
- Location
- Dry Prong, Louisiana
It should be about 1.92a on the neutral.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Dennis, If he's trying to determine what size wire to run for the neutral, assuming he already knows the current that will be used, there would be no wire to clamp yet. Or did I read the OP wrong?
Thanks for the formula- let me elaborate just a bit on what i'm dealing with. We re-fed some casino gaming ckts. with shared neutrals. My lead electrician felt no need to mark the neutrals- now I have to put them back in what will be their permanent location. I have about 30 bundles of 50 conductors and no idea which neutral is which. . . Only idea I could come up with is to try to match the loads.
- Location
- Massachusetts
If you get a group of A, B, C & N that you suspect is one MWBC place the amp clamp around all four conductors and it should read pretty darn close to 0.
Now I feel pretty stupid-I knew that. . . Too much goin on, I guess I was just over thinking this one? THANKS.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Never mind! I see now where he is trying to check with a clamp. I'm going back to bed!
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Sounds like a terrible job. I would bet some of the circuits may have the neutrals drawing the same current so it would not necessarily tell the facts.
You could turn off all the breakers and disconnect all the affected neutrals. Turn one circuit on and touch the neutrals till you find which one it is. A laborious job either way.
You could turn off all the breakers and disconnect all the affected neutrals. Turn one circuit on and touch the neutrals till you find which one it is. A laborious job either way.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
You go first Dennis.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
LOL-- touch the neutrals to the neutral bar.... smarty pants:grin: You aren't afraid of a little juice are you????
kda3310
Senior Member
- Location
- Dry Prong, Louisiana
Please explane, I have never heard that you could do that. How?
All of the current leaving the source must return to the source (Kirchoff) so if there are no alternate paths all the current going and coming in the circuit conductors will add to zero.
Roger
Cant' turn em off until it's time to put em back in the permanent spots!!!Harrah's has a thing about unplanned power losses to their games. I think I can use the formula and check em by clamping them all together and checking to see that voltage is 120 from each phase to the neutral and that will get me close enough until I have to pull new wire for each ckt. with a dedicated neutral. At that time I can fix any problems before changing them over. Thanks for your help!!!!
- Location
- Illinois
- Occupation
- retired electrician
That is not what my spread sheet comes up with for the given phase currents.
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