Voltage drop or nuetral to earth voltage question

[jrscowfarm]

I work at a plant in the electrical and instrumentation department. I would consider myself an apprentice having been in the maintenance dept for 9.5 years now. I was working today on a motor for a pump it was a 5 horse motor 3 phase fairly straight forward but I got into it with an electrician as we kept getting a voltage drop on one leg. it was fluctuating between 12 and 30 volts. As we went forward we found that the VFD card was bad and that was leading us to the weird voltage readings and throwing off our trending for that pump.

While we were working on it He said there is a level of neutral to earth voltage that is allowable on power lines. I said how much?

He didn't know I said I would go home tonight and look it up and if I could find it he was going to buy me a pop tomorrow at work.

I cant find it. :ashamed1:

Any of you guys know if there is a minimum level?

Been lurcking around this site for about a year fnally decided to post something. Thansk for all the insight.

 

[mivey]

I would have to look and see if there us an actual standard but I don't recall an "allowable". That said, I would not be surprised at all to see several volts, even more on a long, loaded, single-phase circuit (one good reason to limit the length of single-phase feeders). I would consider 30 volts excessive.

I have some notes on commonly seen NEV levels somewhere and I'll see if I can find it.

 

[kwired]

I work at a plant in the electrical and instrumentation department. I would consider myself an apprentice having been in the maintenance dept for 9.5 years now. I was working today on a motor for a pump it was a 5 horse motor 3 phase fairly straight forward but I got into it with an electrician as we kept getting a voltage drop on one leg. it was fluctuating between 12 and 30 volts. As we went forward we found that the VFD card was bad and that was leading us to the weird voltage readings and throwing off our trending for that pump.

While we were working on it He said there is a level of neutral to earth voltage that is allowable on power lines. I said how much?

He didn't know I said I would go home tonight and look it up and if I could find it he was going to buy me a pop tomorrow at work.

I cant find it. :ashamed1:

Any of you guys know if there is a minimum level?

Been lurcking around this site for about a year fnally decided to post something. Thansk for all the insight.

You might want to clarify just what kind of voltage you are talking about. NEC doesn't really address some of the possibilities of what you may be talking about.

A required disconnect for say a motor should disconnect all ungrounded conductors from the normal supply, but there is nothing stating there must be something to remove any capacitively coupled voltage that could still be present, but such voltages are typically low volts and have no significant current available behind them and are mostly harmless.

If you had a motor driven by a VFD, nothing says there can't be any leakage through the drive either - it just has to interrupt enough points in the circuit to stop current flow - it is a controller not a disconnect. Actually a VFD is more then just a controller but for simplicity sake lets call it a controller for now.

 

[mivey]

I would have to look and see if there us an actual standard but I don't recall an "allowable". That said, I would not be surprised at all to see several volts, even more on a long, loaded, single-phase circuit (one good reason to limit the length of single-phase feeders). I would consider 30 volts excessive.

I have some notes on commonly seen NEV levels somewhere and I'll see if I can find it.

According to one source (I did not have a note but I suspect Wisconsin), for farm animals it would seem about 2 volts or more should be addressed and over 4 volts for swimming pools and such. Of course we know that 30 volts is definitely a threshold voltage in general but is really excessive for NEV.