IMP

1) http://www.weschler.com/_upload/sitepdfs/techref/gettingdowntoearth.pdf

2) Less than 4 ohms is generally recommeded. Under 2 is of course better. After that, size and current capacity and soil conditions and locations and budgets may impede improved impedances.

3) Zero at the bonding point at the transformer, very close to (stray RF in millivolts?) , or zero at the load center, and still very close to zero at the machine... when no load is present. If you are measuring more than millivolts, and certainly if you are measuring 7-12 volts on neutral to earth (that you mentioned in your other post) when no load is present, you have a huge problem. A single phase load will certainly read some voltage between neutral and earth depending on the load. A three phase load will read some voltage depending on the load balancing and neutral sizing.

As has been stated in this forum countless times before, a voltage on the neutral is simply the expression of the neutral current and the earth loop impedance. To reduce the voltage, simply reduce the neutral current, or the earth loop impedance, or both. The neutral current is the vector sum of all the phase currents. The earth loop impedance can be reduced by increasing the conductor cross-section area of either the neutral or the earth conductor or both.

British Standard 7671 and Indian Standard 3043 both refer, as do countless other national wiring codes.

To be certain Mr Chopra is getting the info he needs, I replied to both his threads to try to help. Please note that he is implying, and my notes comment on this - he has voltage on the neutral when there is no current... no load. So he can't sum the phase currents and derive an expected voltage. That's his problem. But - we both come here for help.

He's also got the problem of having a dang-near zero impedance conductors which must be approach buss-bar proportions back to the transformers, but a contractor who is clearly playing hide-the-ball on the earthing pit.

I agree, you and many others are rightly tired of answering the same thing time and again.

http://cr4.globalspec.com/search/sitesearch?do=show&sort=textmatchrank&srch=high%20neutral%20voltage&order=asc

i) If your interntion is testing the EARTH PIT resistance, then you MUST disconnect the earth strips connected to the earth pit under test.

ii) As low as possible. No absolute values are specified in any Standard.

iii) Ideally ZERO.

Quote "he has voltage on the neutral when there is no current... no load."

I do not know how that is possible. The neutral and earth conductor should only be connected at the main switch. Is this how it is connected?

Hi WarEagle, and Mr. Sawan, and others,

We are having a bit of difficulty defining the problem, and so it's much harder to offer solutions.

I am commenting here only because I just spent six months on a project fighting the same problems, and after all that time, we pulled a 80 foot underground run out of a wet conduit and found a slice in a hot conductor. That was the cause of everything from voltage on ground to computer failures and malfunctions in the video systems and everything in between. The electrical contractor refused to believe that there could be a voltage potential difference between the neutrals and the grounds in the load center panels for the building. That was a bit entertaining, standing in the machine room looking at the meter and being told "that can't happen".

I can't scientifically offer equations and diagrams. I can offer this - we could measure what Mr. Sawan is measuring. Six months of fiddling with earth rods and wires and conductor sizing and watering the yard and driving spikes and taking soil samples wasted a lot of time and money. When they finally got fed up with it and pulled out all the wire, they found the bad wire. They replaced it. The problem was gone.

In other conversations, I think it has been established that the earthing system, and the pits, and the pit impedances, are all "acceptable" and probably not the cause of Mr. Sawan's problems.

Reviewing the drawings, it seems the earthing scheme in front of the transformer is correct. For those who are following along on the other thread, remember the issue is the voltage on neutral measured on the machine circuit after the transformer and load center panel.

Since the neutral and grounding conductor are bonded at the transformer, I agree it does not seem likely that the neutral could have a higher potential than the grounding conductor. However, so far all the attention has been on the pit side of the transformer. As in the project above, I suggested looking beyond the load center for a cause. Is the grounding conductor intact through the panel? What is the impedance of the earthing conductor from the machine location to the transformer, in comparison to the impedance of the neutral conductor?

If the voltage is on everything beyond the transformer, it could be caused by a single circuit on the panel which is in contact with either the neutral or ground at any number of possible spots -

A nicked jacket in a wet pipe or a box connector with no bushing. A whisker on an outlet touching a box or pipe or battleship. A bad outlet. A faulty machine cord, or faulty machine.

So I suggested disconnecting the hot phases from the load center and remeasuring. That's more work that shutting off the panel, but it's effective and certain.

After some sleep and reflection, just turn off the branch circuits until the offending circuit is identified, and the neutral voltage drops to zero, then clean up that problem.

Those of you with more expertise, if you will, please explain for both Mr. Sawan and myself?

TX

Thank you for that explanation regarding your previous location. If the conduit was metal you could have leakage current on the conduit that would cause you problem.

Present location

Have you taken any current measurement at any points on the system to see if there is any current flow on the grounding conductor or neutral?

Quote "So I suggested disconnecting the hot phases from the load center and remeasuring"

Could you just open the main switch and do the same thing? That is a good starting point.

Thanks WarEagle -

I should have said "re-meggered" the phases to check for insulation integrity... Not to measure the voltage on the legs, but to check the integrity of the legs.

There was a lot of finger-pointing about what could be causing the problems on that project.

Part of my frustration with the diagnostic process was the non-methodical approach of the electrical contractor. With a crew replacing branch circuits, and a crew replacing outlets, and a crew re-pulling entrance cables and rewiring switchgear panels, pretty much all at the same time, when one problem might go away another would almost always appear.

This place was plagued with all manner of mystery malfunctions. Examples - dimming the fluorescent 277 fixtures up or down, would cause the video displays to shut off. HVAC on? Wireless Mics good. HVAC off? Mics no good. Doors open in room one? No grounds on circuits in room two (moving doors moved the wall, moved the pipe from the steel, which was acting as the earth since the conductor was never properly installed). Yes, this was engineered, installed, inspected, passed, all done by a licensed company in a major city in the USA. Which just reinforces the importance of hiring the best electrical contractors, any contractor, one can get, and watching over the project at every step. Some of this "go as fast as you can with cheap labor" mentality on job sites is to blame as well.

And, then we had the moment when one worker took a cell phone call while holding a hot leg (why hot, why eight feet long?) out of a 277 lighting panel. Propping himself against a wall for a talk about deer hunting and jamming the live end of that wire into the 208 panel that fed all the AV gear - and why that panel's cover was off - became the next month's discussion and repair.