Connecting Neutral and Ground

how much resitance is there between the earth pit and the earth on the transfomer where the supply comes in ? if its high then theres no connection between your earth pit and the true earth at the transformer

i would guess thats the problem

I have measure the voltage be earth and neutral after connecting the earth pit and found it be 0.8 to 0.9 volts. with this difference is it ok to connect neutral and earth

Dear bmadhu,

Please Note,

It is not a bad practice to do so. But as you say that when you check Voltage between Neutral and Phase that is equal to 160VAC so this shock you vendor about supply (Transformer Condition), Please see supply voltage mentioned on instrument might be 100~250VAC you can power up the instrument any way.

The Neutral is connected to a metal plate buried in the Earth at the Transmitting Station and also at secondary coil (As you mentioned Early).

The Earth is connected to a metal plate buried near the point of usage.

The Neutral is used to provide a reference to the Line Supply.
The Earth is to protect the Equipment by connecting it to ground potential that is same as the usage so potential difference between the user and the Equipment is low if not zero in case of failure.

Regard's

Better connect all electronic equipment between Phase and neutral. Ideally, neutral and earth potential should be same for a solidly grounded system, if you are taking the same reference point for earth everywhere (or) all the earth points in the plant are interconnected. Check whether your system is solidly grounded. If that is the case, reduction in Ph-E voltage at load point may be due to that, earth reference is different from that of source (OR) there is some problem in termination of earthing cables.

Is your supply voltage possibly connected as a center-tapped delta connection? If so, you would get 220 Volts between any two lines, and 120 Volts between two of the lines and neutral, while the third line to neutral would read 160 Volts or higher...

It depends upon the earthing/grounding method (the two terms are synonymous and inicate differences in usage either side of the Atlantic Ocean). Check-out the Wikipedia page on earthing systems and check the system installed against the methods.

For an IT system, connecting neutral to earth at the equipment would be a bad idea. The result would be an over-sensitivity to earth faults elsewhere on the network: particularly bad in, say, a hospital operating theatre where reliance on supplies is needed through complex and demanding procedures.

The critical measurement is the earth loop impedance, which needs to be measured by a competent electrician before the system is energised.

The actual voltage on the neutral with respect to earth is largely irrelevant. A voltage such as 160V on a 240V system may simply be an indication of a blown supply fuse on one of the three phases elsewhere. It may be an indication of the earth conductor being open-circuit (which the earth loop impedance test would show up), it may be an indication that the earthing system is IT, it may be an indication that the neutral conductor is open-circuit (which the earth loop impedance test would pick up), etc., etc..

If in doubt, consult a qualified electrician.

The method I have used (and not killed anyone up to now!) is to connect neutral and ground only at the source. In your case a transformer I believe.

I also dig a good earth pit and have it tested by a competent electrician, close to the source transformer.

I run a cable with 3 cores from there to the point where I need the power. Neutral, earth and phase.

I personally see no reason to dig another earth pit at the point where the unit is to be supplied....

Trying to save running an earth or in this case a neutral wire just sounds very dangerous to me personally.....as that is what it appears you are trying to do (apologies if I am reading you wrongly). I do not believe that is allowed in Europe, but I am not infallable....

You wrote:-

"and to power the weigh bridge indicator we took single phase power along with earth wire from a near my power panel about 200mtrs distance."

Why would you power something between earth and phase? Where EXACTLY was the earth pit? Surely for it to work at all, you must have two pits, one at each end?

I am obviously not understanding exactly what you did.....sorry!

I do like to have some type of overcurrent sensing/fusing on the phase only and earth leakage sensing as well near to the source....

In Australia and S.Africa, they do have a 2 wire system that works well over very long distances via earth pits at both ends.......there is someone from Aussie who posts on CR4 who can explain how it works far better than I......hopefully he will read this and post the details....

try increasing the size of the wire to consider the distance voltage drop or Use a transformer with a 240Vac output near to you weighing system.

There is some confusion in some of the answers:

- You took 3 wires: Phase, Neutral and earth wires from the nearest Panel (200mtrs away) to the weigh bridge. Is this correct?

- If yes, and the Neutral is grounded at the transformer end, there is no problem grounding the Neutral again at just before the weight bridge by connecting the Earth wire + Neutral + new pit. DO THIS just before the weight bridge panel and then connect the 3 wires to the panel requiring the Phase, Neutral and ground wires.

- Doing the above is as if your weight Bridge was near the Original Transformer and I cannot see the problem (?)

- the 160V Neutral to Ground is probably due to capacitive loading due to the length of the cable and should be checked by connecting a 220V rated LAMP between the Neutral and the earth wire: The LAMP should not Glow and the 160V will have become almost zero if checked with a voltmeter. IF IT GLOWS continuously and the voltage remains high above ~10V, then there might be a problem (leakage) with the cable's conductors!

I certainly agree about the confusion here, you have seeming brought some more....(I am only helping a little bit in that area!!)

The OP has never stated exactly that he ran 3 wires, in fact he only mentions two......he does need to state exactly what type of cable he has used.....and how many cores it has.

Linking neutral to ground twice, is (as far as I am aware) considered to be a bad thing as you can get circulating currents through the "loop" formed.....it should only be connected once at the source end only.

Also, it negates the safety aspect of having a seperate earth wire completely (assuming a 3 wire cable), so the connection is both pointless and really dangerous as well.....but I have seen amateurs do this and think they are doing the right thing!!

If he is showing vast voltage differences between neutral and earth wires at the point where he is supplying the bridge electrics, then I feel that he may have not run a cable that is heavier enough for the distance or the volt drops!

Furthermore a second earth pit may then be required at the bridge end to my mind (open to correction on that point from someone better versed in such systems....), but certainly TWO earthpits are required then, not one as the OP implies in his original post.....

As I mentioned before, he also should add both over current and ELCB equipment to safeguard any users.....at the transformer end would be better or at both ends suitably "staged"....

It may turn out that installing the step-down transformer near to the bridge and running the higher (?) voltage lines further might have been a better move as currents would be lower/voltage drops less and the need for a neutral would be negated completely between the bridge and the supply......but that probably does depend on what HV he was using......(I am not a HV engineer!)

If the voltage between neutral and earth is fluctuating between few volts(say 1 to 2) is there some thing wrong or is it because of fluctuating load?

I would say that is completely normal and is due to the load on the neutral /voltage drop.....also 1 or 2 volts is well within allowed tolerances (in my experience).

Andy,

The OP Stated in 1^st Paragraph: "......we took single phase power along with earth wire from a near by power panel about 200mtrs distance. Before connecting ... we measured the voltage between neutral and ground it was surprising to found it was 160V Ac and Phase to neutral 240v AC."

- Therefore, He must have taken 3 wires down to the panel which is 200 metres away. I cannot see him measuring Phase to Neutral across 200m(!?).

Then he wrote: "We made a dedicated earth pit near by and made neutral and earth common which is connected to earth pit with a 16sqmm singe core wire. ..."

- Therefore he made a new earth pit dedicated to this new panel.

As you can see, He 1^st took a ground wire from a distant panel: I think that this ground might not be very good or firmly earthed, therefore creating a parasitic voltage or a voltage drop due to high resistance to earth (?). That is why I suggested he uses a Lamp to check Neutral to Earth at the new panel -> it will show if the voltage was a simple induced voltage that will not draw any substantial current OR due to earth resistance and will draw some substantial current! (he might have some Neutral current going to the earth wire (splitting) and No RCD (current elcb) on that circuit to trip...).

** In my humble opinion, since he made a new pit for grounding, he can use it to connect the neutral to ground at that point then take an earth wire (common to the Neutral...) to the new panel as earth for the New Panel. Then install an RCD (residual Current Differential circuit breaker) to protect the circuit downstream. (IT Does Not seem to have One on the previous tapping panel...? otherwise it would have tripped when he joined the neutral to the ground...)

I hope this is OK with you. Thanks for the input.

I like your post, but you are too trusting (its a nice way to be, but not 100% safe....)

I will read the original post again......but it would be nice if he "stated" what he did exactly......for instance we know he has one earth pit, he might have two or more.... etc etc....

Thanks for you post.

--------------------------

Back again.

You are probably right about the cable, but I still don't like what he did with earth and neutral at the bridge. It will cause errors, waste power and is incorrect....

Something is wrong if he has 160VAC between earth and neutral......maybe he never bonded at the transformer? He as an earth in a pit and no bond - just a guess - so they have no relationship together, now he wants to bond both at the bridge??????

No wonder the bridge vendor is getting worried!!!

Power System Neutral ( ie.STAR Point of Power/Distribution Transformer ) should be directly connected only to nearest Earth Electrode/s to ensure effective grounding of solidly grounded Power Systems which is a normal convention for 415V systems.Connecting Metallic Enclosure/Body of the Equipment/Device/Panel/Control Box (which is not supposed to carry current under normal condition) to the Safety Grounding Network provided for the Plant/Unit is a must for safety of personnel and equipment.But, connecting the System Neutral available at the consumer end directly to the Earth Electrode of the Safety Grounding Network at the consumer end is not advisable.

415 V System normally feeds a number of single phase consumers and hence all the three phases are not likely to be uniformly loaded ,thereby leading to unbalanced system conditions.The resultant unbalance current needs to flow back to the System (ie.Transformer) without any interruption to ensure its detection at the source so that a protection relay actuates if the set value is exceeded. Hence, multiple grounding of System Neutral is not recommended.

You may connect the body of the indicator box/panel directly to the Earth Electrode near Weigh Bridge in stead of the earth wire taken from the source.If required, additional Earth Electrode may be provided locally.

Hope this satisfies your query.

Cheer up !

S PRADHAN

You are correct. But he should not bring the extra wire (earth) from the previous panel.

By grounding the new panel to a separate earth, he must check the earth resistance at this new pit and make sure it is low(<~1Ω). His neutral to earth voltage at this panel should be ~< 2-3 Volts.

Your post has a lot of good sense in it that fits well with my personal knowledge....

Only this:-

You may connect the body of the indicator box/panel directly to the Earth Electrode near Weigh Bridge in stead of the earth wire taken from the source.If required, additional Earth Electrode may be provided locally.

Makes me a bit worried.....I don't think that is generally allowed in Europe (same voltages)......no connection to the earth wire AND maybe not having a second pit at the transformer AND maybe not having a good connection between the pits - maybe - Could kill someone if a fault arises on the frame (phase to frame) of the equipment......

Maybe I am old fashioned, but I like earth fault currents to travel over copper and be sensed by earth leakage equipment.....having an earth pit as well is great as an extra....having two even better!!

Thank you for the compliment.

I appreciate your concern for the safety of personnel.We are also equally concerned and do take all safety aspects into account while designing the grounding system.Perhaps I should have elaborated a little more.

In this case,I presume that,the source Substatin where the feeding Transformer is installed, must have been provided with a properly designed Safety grounding Network comprising of a number of Earth Electrodes(EE) duly interconnected through underground earth conductors of required cross section to achieve the stipulated overall earth resistance as per standards/norms.The STAR point of the Transformer 415V side(ie. System Neutral ) is normally connected directly to at least two nearby EEs (of the aforesaid Grounding Network) through separate earth conductors for system grounding.Further,body/frame of the Transformer is also connected to the said network at two separate points through independent earth conductors for safety of equipment.

Similar Earthing Networks are also provided at the consumer ends.Such Networks of various shops/units of the Plant/Factory are further interconnected thereby further reducing the overall earth resistance of the plant and enhancing the safety.Hence running a separate earth conductor from the source upto the consumer end is not required.

To ensure the safety of the personnel and equipment/panels at consumer end,their earth terminals can be connected to the local earthing network at two separate points each.

Hope I am clear now.

S PRADHAN

You have not mentioned Neutral here, you may have mentioned it before, but for reasons of clarity for all concerned, please elucidate. e.g. Define WHOLE setup clearly as you see it.

I personally find it difficult to follow (as we are talking a BIG safety issue here) EXACTLY when details are spread over several posts.

It was a great start and I thank you most kindly for that.

You imply that in India(?) that you can have an earth return earth path?? and you do not need any form of ELCB??

Here we need the copper return path to the substation in a modern installation.

Or when no earth is supplied, we have an "in-house" earth neutral copper connection. This tends to be in older installations.....

I understand (from other posters only) that the OP user has a 3 wire cable, though he has not stated that explicitly enough for me (but some others read that into his original post!).

If true, how should the whole system be connected? Surely not with an earth pit only at the bridge end as implied??

My take was that he only had 2 wires run and was measuring a high voltage between the earth pit and neutral (which would imply that the earth to earth pits are not fully and or properly installed = a high resistance between the pits..... My take might be completely wrong, but until I see something unequivocally stated, I do not believe it!!! I try to err on the side of safety....

Thanks in advance and for your understanding....

I just read your second post which adds important infos. Shame you did not see fit to post ALL infos in one post together, but better late than never, many thanks.

well, if am not connecting the neutral to earth at the transmitter power board, as i said i have this induction voltage of 160v between earth and neutral. How do i address that.

and regarding connecting a lamp between neutral and earth and checking whether it is due leakage or due to capacitance of cable, i think it could be the possible reason. Need to do this excersice

The exercise is pointless, for instance, what voltage and wattage lamp will you use?

If for example you pick a 240 volt lamp. it may glow dimly red at say 20 volts, it will be quite bright at 160 volts or maybe even burn out. So?

If for example you pick a 110 volt lamp. it may glow dimly red at say 50 volts, it will be quite bright at 160 volts. So?

Such a voltage difference is probably due to the volt drop over the too thin cable.....or it could be due to unbalanced loads over the 3 phases (assuming a 3 phase transformer), or it could be due to not bonding the earth and neutral at the transformer correctly or not at all......there could be more reasons that I have not even thought about.....

Bonding near the load (away from the source) is wrong.

Bonding twice is wrong.

Having severely unbalanced loads is wrong.

Having too thin cable, promoting voltage drops is wrong.

and and and......

You should get an expert and do the job properly....Asking here is OK, but you must also follow the local code and do it as safely as possible.

Bmadhu, (Andy)

OK, I understand the safeties involved. The most important at this point is finding why there is 160V between the Neutral and Earth wire coming from the nearby(200m away) panel.

For this I suggest that the OP goes back to the panel and checks the Neutral/Groundwire voltage using a voltmeter:

- If the voltage difference is 160V or near that value, then he can also check it with a lamp test (usually having a 220V 40W or 60W ) just to eliminate the possibility of the voltage being just induced through the insulation/proximity of the 3 cores & by the way, if you are using a 3 cores flexible cable, this is common!

--- If the lamp even glows dim, this will indicate that there is a leak---> disconnect the outgoing cable and repeat the test with just the terminals on the panel: If the same happens, then your problem is within that panel or before it AND IT IS SERIOUS---> get a good electrician to investigate...

--- If the lamp does not glow, check with the voltmeter while the lamp is stil connected: The voltage should be very low ~ few volts maybe. If higher than 20V then as above repeat with the cable disconnected. Use the same logic ( ----?--- electrician).

----- If the problem exists only with the cable connected, then the cable is either bad and lesking from the phase core to the Earth core or the quality is such that there is a parazitic induction: Depends on the results of the lamp test. ==> either change the cable (if leaking strongly---lamp glowing at the test from the end of 200m) or make sure that your new nearby earth pit is having a good low resistance (indicating that the source ground connection at the transformer is adequate ) and use it as earth.

Alternatively (from the last case above) run a separate earth conductor if the earth at the 200m panel is proven good!

Ideally,Star point of the power transformer is at ZERO potential and hence connected directly to Earth Eletrode in case of solidly grounded power system.Since unbalance current flows in the Neutral of 415V AC system as explained in my earlier post,some potential is bound to appear at any point on the Neutral conductor with respect to Earth, depending upon it's distance from the STAR point of the feeding Transformer.Therefore, it is not advisable to connect the Neutral and Earth conductor together with the Earth Electrode at the consumer end.However,Earth terminals of the Panel/Control Box/Motor etc should be connected to the local grounding network at consumer end for safety of personnel and equipment.

Hope ,I am clear.

S PRADHAN

Now we have to find out from the OP just how near to your posts he has installed his system, I am expecting some major ommisions, hopefully I am completely wrong.

What you wrote in your last two posts makes good sense and fits in with my (ancient) knowledge exactly. So India installs in a very similar manner to Europe....

Many thanks again.

Tank you so much Mr.Andy.

I am sorry to have caused inconveience to you by not covering the whole stuff in a single post.In fact ,I was trying to answer specific questions put by individual members.

Yes ,we also use ELCBs in small systems like domestic /commercial/hospitals etc.

S PRADHAN

Stop commenting ,the guy had a problem three years ago. This is not to start discussion. Thanks