Find Earth to neutral voltage

Earth-to-neutral voltage will vary with the current drawn in the neutral conductor. There is no 'specification' to it as such. It is not uncommon for it to be around 10V in some areas. The procedure to measure it is to place a voltmeter actoss the neutral and earth terminals.

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

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

The question asked :- what should be a earth to neutral voltage

It is healthy system, where no voltage between earth to neutral.

The question should have been asked as :-

* If there is volagte between earth and neutral, what should be the reason ? and solution

* What should be allowable limit in case, if the voltage between earth and neutral exist ? / OR what is limit for safe voltage between earth and neutral?

nascon

In all service panels that i have worked on the neutrals were connected to ground. So there should be no voltage. That all so depends where you are taking the test voltage from. If at a device on a long run from the panel may have some voltage I say millivolts. 10 volts is high and i would say you have a problem.

You have received some excellent answers, but what do the regulations say in your (to us still) unknown country as to the max allowed???

As low as possible is my personal take on this subject.

Some countries allow earth to neutral bonding in each house, some don`t......what does yours say?

If you measure voltage between ground (earth) and neutral, then there is a problem, it could be dangerous and it should be corrected.

You will nearly always measure a voltage difference, it just depends on :-

a) how far away from the neutral earth/link you measure and

b) what the load is on that circuit at that time.....

The rule is to not let it exceed certain fixed parameters, regulated & local to you in your country!

when you measure voltage between neutral to earth across the grid (mains) circuit , you get some thing between 1v to 12v , it has something to do with impedence in mains circuit, we used to install sofisticated instruments & machinery & manufacturers recomended good earthing with power back up even values were fixed between 2v to 5v but no 0v ( reason ,open earthing will show same) , image setters (four color seperation), digital printing machines ,digital photo machine, could not be calibreted without good earthing , manufacturers recomended seperated earthing for power back up plus the machine , we also made observations on assembled online UPS where earthing & neutral were shorted with DC gnd aswell , output of ups between neutral to gnd 0v (obviously!), this seemed unusual and they didn`t work properly seperate earthing directly to machine was screwed to avoid damages and shocks . but 10v or so is wrong earthing and it is serious problem , buildings and other constructions often have dedicated earth running throughout electricals.

You should never measure a voltage difference between neutral and ground at the main panel where the utility power first enters the facility since it is required that the neutral be grounded in the main panel. However, if there is a subpanel being fed from the main panel, the length and size (AWG) of the feeder neutral to the subpanel, and the load on the subpanel at the time the measurement is being made will determine the voltage difference between the subpanel neutral and ground at the location of the subpanel.

Per the NEC, the only place the neutral is to be grounded, is at the transformer supplying the load center. The neutral and grounding buses in panels are supposed to be electrically isolated though that is not the way it is usually found. Ground fault breakers typically tend not to work to well when the neutral and grounding buses are bonded together.

You are perfectly correct in my estimation.

The bonding of earth and neutral in supply boxes is something someone else mentioned, that I personally have no experience of.....

I disagree. Unless there has been a recent major change in the phylosophy on grounding (which I don't think there has been), NEC 2002 Illustrated Handbook, Article 250, Exhibit 250-1 clearly shows both the transformer neutral and the customer service panel neutral bus being solidly grounded to a grounding electrode.

It makes sense that you would not want to rely on soil conductivity to provide a ground path back to the utility transformer neutral for fault current to trip the breaker of a faulted circuit.

I am missing something, why would you need to rely on soil conductivity???????

If the neutral isn't grounded at the customer main panel, then earth becomes the only path from the faulted cable or device to the grounded neutral at the utility transformer. If soil conductivity is poor, there will not be sufficient fault current to result in the branch circuit breaker tripping and clearing the fault.

Eh? That diagram shows a two-phase supply! There's an earth/ground conductor, but no 'neutral'! You've got two live phase conductors and an earth bonding conductor, but there ain't no neutral there, innit?!

Or that's what the manual that I nicked from the blokes working at the substation says. <Sneeze>.

Pete

The neutral conductor is the center tap of the transformer which becomes the return path for the each phase when used individually for 120V circuits.

What would you consider a neutral conductor to be?

In all the systems I have seen, you might link/Bond to earth spike and metal water pipes etc., but the earth is still a wire going back to the substation!

I would have thought that soil conductivity can never be relied on for safety reasons......dry summer, soil with bad conduction anyway etc etc.

I have been told that in Australia, in the outback, they sometimes use a huge metal sheet buried deep underground to get an earth return. I have never seen this, but it strikes me as at least theoretically possible. I once saw one of their Australian hot water jugs, with a bare element, immersed in the water, in a pottery jug with a plastic lid.....it horrified me....especially as it was being used by an RN colleague (who had bought it in Australia)in the UK......!!

An ex-girlfriend came back from South Africa with a waffle iron that gave shocks, I picked it up by the plastic handles and touched a metal part to a grounded gas cooker, it blew the mains fuse (UK). I found that one side of the element was connected to the metal frame, the amateur electrician had connected the live to that side of the cable.....it could have been connected the other way around, but still to my mind dangerous, I bought her a new one instead....

Here in Germany, we get an earth wire from the transformer.....I believe that generally speaking, that is the preferred method in Europe.....

In NY City, surely they have proper grounds, even though you only have 115 volts or thereabouts? Or is it not a requirement with such low voltage?

It's no different in NY City. There is always a hard wire return path to the transformer neutral as shown in the NEC Exhibit 250.1

Many thanks for that statement, I agree entirely.

So soil conduction does not play a role in this area, just as I thought.

'Cos in a TT distribution system, that's the return path for the fault current! That's why in the UK you will find a 100mA delay RCCD across live and neutral on the input to the house upstream of the main distributon box in an installation that is fully compliant with modern regulations. With TT, the live and neutral usually come in overhead. If there are three conductors L, N, E, a break in the earth conductor only because of a fallen tree branch might prove fatal to an 'earthed anyone' grabbing hold of a fault. That is why you only have L and N overhead and the fault current goes via soil conductivity as the earth conductor. The 100mA RCCD ensures that the trip goes off at 100mA, and not at 32A on the individual circuit breaker for, say, a power shower. 32A needs a much lower soil conductivity to operate as compared to 100mA. In TT distribution, the maximum earth impedance is supposed to be 50Ω. At 240V, a regular 32A circuit breaker wouldn't trip at that impedance. At 100mA, it will go at 5V tops, which isn't usually fatal. At 30mA, the normal trip rating for the RCCD downstream, the voltage is something more like 1.5V. Torch-battery levels.

Or at least that's what the horrible old bat in the next box along told me. <Splutter> She knows much more about this sort of stuff than I do. <Cough>

I'm not familiar with the abreviations you used, but it does sound like distribution differs in the US from the UK. I'm interested though. Can you send me a sketch of what you described?

gfh