Neutral-Ground Voltage

he says the voltage will be lower than 1 volt.

No, it doesn't sound reasonable. It sounds abstruse.

http://en.wikipedia.org/wiki/Earthing_system

http://en.wikipedia.org/wiki/Ground_and_neutral

Seems that in certain conditions it could... in others, it would have virtually no measurable effect.

What's the problem you are trying to solve?

I have an electrical engineer friend that lived in the UK that had this condition. He installed a transformer between neutral and ground and stepped up the voltage to power his refrigerator. When he was young and poor, the money he saved was significant.

a transformer?? i cant imagine such a thing in reality, what will do a transformer and also why he boosts the supply voltage to the refrigirator? İ Think you must first of all tell about the problem of the refrigerator.By the way with capacitor i think the aim was to lower the neutral-ground voltage so that sensitive devices dont get burnt,

He turned a problem, voltage between neutral to ground, into an oportunity. The neutral to ground voltage was 9vac. He boosted it with a N = 9:230 turns ratio transformer that he made so that he could steal electricity. I am not stating that this is what you should do.

If I had a floating neutral problem, I would check to make sure that the electrical service panel had a proper ground, ground rod placed into the ground and also connected to the water pipes. I would also make sure that the neutral coming from the utility was also connected to the ground at the electrical service entry.

Well, it depends upon the earthing system applied locally. Connecting neutral to earth/ground in an IT system will have no measureable effect whatsoever.

Connecting neutral to earth/ground downstream of an RCD will result in the device tripping on occasions.

Earth/ground is a safety conductor, first and foremost.

See #14. Neutral to Equipment-Ground shorts are not permitted (outside of the Service Entrance).

I do agree with U that a neutral voltage exist but only in an unballanced system. So what do you intend to do with it? Connecting a capacitor accross neutral and ground for a 2-3 volt to go down is for what purpose?

I will like to hear more of this.

Dickson

I think it is up to the IT systems and ground loops, i dont know exactly the case, just been told of it, in fact the high neutral-ground voltage (not because of imbalance but i think because of leakage return through neutral point) causes ground loops and they cause the electronics cards devices etc to burn, if i am wrong excuse me, it is said that a professor adviced to connect a capacitor across neutral and ground terminal of a devices so that the company which is supposed to give guarantee for the device would be contented to give it , (otherwise the company wont give the guarantee papers ), i am not so versed in these subjects and just share my opinions here...

"Snake oil"?

I spent several years inspecting the environmental, power distribution and grounding systems in the Tri-State area around Pittsburgh PA for the customers of a Super-Minicomputer Company.

Our concern was that the customers were not getting the best from our computers because the power quality, grounding and environment were not nominal for the computers. Since the top-of-the-line bleeding edge (at the time) computers used emitter-coupled logic, they were quite sensitive to ground loop currents passing between the computer racks.

Almost all the significant problems I encountered involved shorts between the neutral and equipment grounding conductors. I can categorically say that the capacitor shunt is a bad thing, and high neutral voltages never had a whit of detriment to data processing quality.

On the other hand, our switching-mode power supplies had everything to do with the high neutral voltages, since we originally produced them all in Wye configuration. The neutral current was typically 1.4 to 1.6 times the load current, and the frequency was 360Hz with large harmonics. Since then I have started to see the same thing happening with electronic ballasts.

Please note that with switching-mode power-supplies, even a perfectly balanced Wye load will produce very large neutral currents, with a theoretical upper limit of I(neutral)=Sqrt(3)*I(phase)=1.732*I(phase). This is the justification for derating such circuits to I(phase)*Sqrt(3)/0.8=I(phase)*2.165=I(capacity)