Grounded and bonded system
- Thread starter chris.s
- Start date
- Status
- Location
- Massachusetts
Either loose connections or simply voltage drop on the neutral conductor, or a combination of the two.
I should clarify the this is a nuetral on a 3 phase 230/400v grounded Y generator feeding multiple buildings(in Iraq). I am assuming the the three voltage vectors should sum to zero as the three current vectors would in a balanced system. I am seeing differences from 2 to 8 volts and I'm starting to question if the installation is correct??
- Location
- Massachusetts
chris.s said:
The current on the neutral, forgetting harmonics will be zero if the system is balanced. But in the real world it is hardly ever perfectly balanced so there will be current on the neutral and there will be voltage drop. That voltage drop can be measured against the non current carrying equipment grounding conductor.
In my opinion 2 to 8 volts is not much to worry about, especially if the distances are long.
If you want to nail it down, start at the bond (N to G 0V) and keep taking N to G readings toward the spot where you measured 8 volts. You will be able to find where you dropping the voltage.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
If, as Iwire notes, there is current flowing on the neutral conductor, then the voltage difference between the neutral and the equipment grounding conductor can simply be caused by normal voltage drop (say if you have long runs or a small neutral), or it could be caused by poor connections in the neutral return path.
Another possibility is that you have a bad equipment grounding/bonding conductor, with local grounding via grounding electrodes but no true connection between your neutral/ground bond at the source, and the grounding bus at the panel. In this case, you _may_ be measuring the difference between local ground at the source and at the panel.
Finally, I think that you have a small error in your assumptions. In a perfectly balanced situation, the vector sum of the three phase currents should be zero. However the_purpose_ of that neutral conductor is to permit the flow of unbalanced currents. If you have any unbalance at all, you will have current flow on that neutral, and if you have current flow on the neutral, then you can have voltage drop on the neutral.
-Jon
Another possibility is that you have a bad equipment grounding/bonding conductor, with local grounding via grounding electrodes but no true connection between your neutral/ground bond at the source, and the grounding bus at the panel. In this case, you _may_ be measuring the difference between local ground at the source and at the panel.
Finally, I think that you have a small error in your assumptions. In a perfectly balanced situation, the vector sum of the three phase currents should be zero. However the_purpose_ of that neutral conductor is to permit the flow of unbalanced currents. If you have any unbalance at all, you will have current flow on that neutral, and if you have current flow on the neutral, then you can have voltage drop on the neutral.
-Jon
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