Connecting Earthing to Neutral

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

According to National Electrical Code (American) the only place the neutral can be connected to the ground is at the primary distribution panel where the ground (Earth) is connected to a ground rod driven into the earth, and where the ground and neutral id connected to the buildings plumbing and other metallic items. from the primary distribution panel onward the neutral and ground must be separated. For example on a single phase sub panel four wires must Be run from the primary distribution panel, L1, L2, Neutral and Ground. the Neutral must be isolated from ground at the sub panel.

The philosophy of such connections is that the resistance of the wires of a line conductor and a neutral conductor are about equal from any point, therefore a short circuit from a line terminal to Neutral will result in half the line voltage appearing at neutral to ground, at or close to the location of the short circuit and even though the fault should result in an immediate circuit breaker trip the instantaneous voltage at or near the location of the short circuit can and has caused shock to personnel and fire. Also failure of a circuit breaker has occurred causing a shock and fire hazard.

Hope this helps. CEKM

Yep! I had to go through this when I altered an outside box of a house originally designed for 40 Amp service, and the inspector told me about a whole bunch of stuff I was going to have to do.

"So, I guess I won't" I said.

"Oh! You touched it, you bring it up to 100 Amp code!" said the inspector.

I was trapped! Also, he explained that the reason why the ground wire had to run to all the pipes is because some plumber got shocked (killed?) once, so now it's code. Makes sense, it just sucked putting out all the extra cash!

your point is still not clear to me, well if i connect N-G at sub-panel, what will happen, is the ckt run?

Manirul,

if you still do not understand the reasons (which have been well and fully explained by other posters for you) then leave well alone and get a professional in.....

Do not work on equipment that your background and qualifications doe not allow a full and complete SAFE understanding of what you are doing.

Nobody is perfect!

If you connect the Neutral to ground at a sub panel then in the event of a short circuit from any L terminal to Neutral will result in the sub panel and all items connected to the ground buss through the ground conductor being energized at near one half of the line voltage, I say near because some voltage drop will occur in the wiring from the sub panel to the point of the short circuit. Under short circuit conditions the circuit breaker should trip instantaneously, however the shock and fire hazard will exist until the circuit breaker opens. In fifty years I have experienced two cases where the branch circuit breaker failed to disconnect, the instantaneous current was sufficient to weld the contacts in the circuit breaker before it could release. In both cases the insulation on the branch circuit wire melted. In one of those cases the wire was in rigid conduit, the melted insulation stuck to the inside of the conduit, the conduit had to be replaced along with the wire.

I have noticed when I worked overseas where the British system was used that a Ground fault detector tripped the main circuit breaker. Here in US Ground fault circuit interrupters are required for hazardous and wet locations, and GFCI circuit breakers installed in the distribution panel to protect only the branch circuit. Also GFCI receptacles are installed in wet locations such as sinks and washtubs, GFCI must protect any receptacle within six feet of such items. GFCI receptacles can be connected to protect additional receptacles down stream of the GFCI.

Hope this is not information overload and is helpful. CEKM

Good info, thanks. No (mental) overload!

sukran CEKM

your explanation have more clarity.

If you connect the neutral & ground in a sub panel, any neutral voltages will be on the ground wire. If you touch a piece of grounded metal you may get a mild to severe

shock. That is why all neutrals and grounds are separated back to the service entrance.

Good luck,

James

While wiring My shop I did what You propose. When power was turned on, BAM! instant short circuit and tripped breaker.

oilcan13

I think he has to endanger himself before he will believe us all.....

Andy, you should know, that with some people, you can tell them anything........BUT you can't tell them much.

The only problem is they may not just only injure or kill themselves.

Thats my worry too, some have to learn by getting themselves featured on Darwin Awards.....its the sort of "Final frontier" of learning!!!

Dear Andi and Mobi,

I'll be very specific and I hope you'll be as well without any hard feeling.

Consider an isolated industrial system (the neutral is not connected to the earth) while all electrical devices' enclosure as well as all metallic non-electrical devices (tanks and vessels for example) are connected directly to a very good earthing mesh.

Do you think that system is safe or not? (Yes it is safe)/(No it is not) from the human safety point of view.

If not, please explain.

Thanks

Samak

Yes I do consider this system safe, as this is precisely why electrical systems aboard ships are not grounded to the hull. The philosophy is that one line be it neutral or L may be inadverently connected to the structure without harm, that's the first casualty that can occur without harm. a second conductor connected to the structure would then cause a short circuit, and perhaps cause damage. Thus in a ungrounded system the first unintentional ground causes no harm, and a warning is received through the ground monitoring system. A simple ground indication system is to have small wattage incandescant lamps connected from each power conducting conductor to the structure. When no ground exists all lamps (Two if single phase, three if three phase) will glow at equal brightness, at half brillance, the system voltage is applied to any two lamps in series. If a ground occurs, the lamp connected to the grounded conductor dims, only partially if the ground is high resistance, or completely extinguished if the ground is a low impedence or direct ground.

The danger of this simple but effective ground monitoring system is that a small spark may be generated in the event of a ground, not a good thing if the application is for use in the prescence of flamable vapors, which if I "Read between the lines" your application is.

A better solution is the use of ground impedence monitors which monitor the system resistance to ground electronically. We have several of these monitors on this ship, they work well, and can measure resistances up into the tens of K ohms, indicate which conductor is effected, and have an adjustable sensitivity alarm setpoint.

On this ship we have harmonic filters on some critical circuits which consist of inductive and capacitave components connected to the ships hull. Therefore some current flows to the hull through the capacitors and shows up in the ground monitors as a high resistance path to the hull though when read with a megger or ohm meter shows infinite resistance. We are able to set the threshold of the alarm to compensate for this high impedance path.

Hope this helps you, I can supply with the manufacturer and source of these ground monitors if you request.

Regards CEKM

Samak, No hard feelings, just needed more information about the problem.

Hamsa sannan anna nokhada marakat al samak bin Muscat

Kfalik, Salam Al Lakim Sabat Al Haier

As you have not given enough specific and valid detail to be able to answer your question exactly AS TO WHETHER AT THE LOCAL SUBSTATION THE N TO G CONNECTION HAS BEEN MADE OF NOT. I cannot give you a finite answer. It seems you feel that the substation has NOT got the N to G connection.....

In my experience there is only one connection made between neutral and ground, and that is at the substation where the final "User" voltage is produced. Not before that and not after that.....if it is missing, that is wrong.

I had thought that other posters had made that abundantly clear, but you seem to want to ignore their advice for some reason.....or you simply do not fully understand it.

Lets see if this helps you further:-

Having more than one N to G connection is wrong wrong wrong.....

N to G connections in the area of the user are wrong wrong wrong.

Not having one at all is wrong wrong wrong.

In most countries, this connection is made by the electricity supplier, not the User.

Not having it is dangerous.

Having it in the wrong place or too many is dangerous.

Usually the only grounding that a building needs is an earth bond from the main electrical box, to all metal water pipes and to a ground spike driven into the ground, deep enough to make a proper connection. This is a safety question ANSWER ONLY, there are also "signal" reasons for grounding that I am not competent to answer as it is a very specialised area where certain special frequencies must be shielded. I do not feel that is the reason for your questions....

If you need to ask somebody on CR4 about this, you are not competent in this area and should leave it to professionals. You can cause so much grief unintentionally by what might appear to be only a small mistake....fires and possible death to people in the building, not to mention electrical or electronic equipment can also be damaged....

well, you have saying all those wrong from your vast experience and we also agree with you, but question is why? any logic? if N and G shorted at one point only and where ever you check continuity it will show short then if we connect N-G second time what is wrong with it? any technical reasons?

Please read the following link on safety with regard to neutral & ground, it explains the whole situation very clearly I feel.

You too could have found these yourself with a minimum of effort on your part......!

Neutral/Ground Safety

NeutralGround.pdf

If you don't understand this, then do as I suggested earlier, do not touch this equipment or make any unauthorised changes....

In Australia the MEN system is used. The Neutral to Earth is made at the main switchboard then to a secure earth stake. Similarly any distribution boards in out buildings must also have their own separate MEN system.

In low voltage marine electrical systems, shipbuilders (fishing vessels) often use the cheap earthed electrical systems, when this occurs the MEN link is on every alternator and not on the main switchboard because of problems associated with shore power when alongside.

I believe that in most civilized countries your first paragraph is 100% true.

To all,

I must correct myself, as all of you are correct, and my answer neglected the fact that the supply if terrestial does require a neutral to ground bond at ONE place. However if the supply is from an isolated source, IE a portable generator, or through an isolating transformer a "Floating ground" with ground fault monitoring is acceptable and safe, and can be used for special applications.

Regards CEKM

"Floating ground" with ground fault monitoring is acceptable and safe, and can be used for special applications.

This is the system used in the best of electrical systems in marine applications whether elv, lv, both 240V single phase and 415V 3 phase with, as you correctly said, an simple "earth leakage" testing system. This ensures:-

1. Safety of the crew from electrocution.

2. Continuity of supply.

3. Improved control of corrosion of machinery and the hull particularly from stray electrical current.

Dear All,

You are obviously right, in all commercial, residential and most industrial networks neutral (N) must be connected to earth (E) to avoid:

1. neutral voltage-rise resulting from unbalanced load or others.
2. transient voltage spikes resulting from switching or others.
3. phase voltage rise in healthy phases resulting from line-to-ground faults in isolated-neutral systems.
4. may also to provide a sensible enough fault-current for protection devices to respond for the 1st. fault.

Almost all of us know UHDE, it is a big engineering contractor in Germany, Andy knows it very well, I guess. In my country, we have more than 7 fertilizers/Ammonia industries, all had been made by UHDE, and all are based on isolated-N 6.6KV network. The reason of that is to increase the reliability of the electric energy. In most, may be ALL, chemical industries of which the process must be kept running to avoid a huge amount of losses, the system's neutral is not grounded, consequently the system may be operated with a ground fault present, improving system continuity. But,

all of the touchable equipments' cases (external bodies) are connected to a very good grounding mesh in more than one point, forcing the surface potential to equal zero volt even in case of ground fault (i.e. connection between a line and the equipment case).

Is that safe or not???

ALakom Salam CEKM

You have brought up a different system, probably Delta connected, no neutral, so what are you trying to prove? This system is quite different, different safety measures need to be taken, end of story!!!

This does not make a wye connected 3 phase system with neutral correct, when the neutral and earth are not correctly bonded...

Its almost like comparing chalk and cheese, both are off white....so?

Andy,

Point well taken, however you should be able to access US Code Of Federal regulations on line, read CFR 29 1910.304 (f)(1)(v).

Regards CEKM

OK. Here's a question you can answer for all us non-electrician types...

So, I'm sitting in my little apartment, and I have the plug for 110V AC appliance in my hand. It has three prongs - One is power, one is neutral, and one is ground, correct?

Now, almost everyone is taught early that there must be a + and a - for current to flow. How do I apply this concept to this three-prong 110V AC plug?

It would seem to me that in an AC system, current first flows one way and then the other. So power and neutral are necessary so that AC current can go back-and-forth to the power station. If this is true, then ground is just there in case it's needed to keep people from getting electrocuted?

Also, if both power and neutral are needed for AC current to flow, how can I make sure that power was really connected to power and neutral is really connected to neutral? Also, if AC power flows back-and-forth on power and neutral, why aren't they interchangeable?

This may be too simple, but, please, indulge me!

I cannot answer this fully I feel but you have to differentiate between relatively dangerous systems of AC and relatively safe versions.

In Europe generally, they use a system that allows the plug to be used either way round, mostly in the US too on small load items I believe. I as a Brit find this system dangerous. (I know you only have 110v in the USA, that helps a lot).

The British system, that appeared (memory) sometime in the early 50's I believe, is a lot safer (provided it is correctly installed as for any system!).

Why? You may ask.

Well the plugs are polarized (British Standards 1363), so that phase and neutral have their own pins, as does earth. You cannot put them in to get the phase and neutral the wrong way round.

The holes in the wall socket have little windows that cover P + N until the earth pin pushes them down so that people cannot put pins, pencils or anything else in an touch a live connection. Only earth is open for such things!

The P + N pins are shielded with plastic, so before they make contact to the internals of the socket, only plastic can be touched accidentally on these legs.

Each plug has its own fuse, set to the correct level for the device at the end of the cable. In a normal situation, only this fuse blows. Not a circuit for half the house....!

Each socket usually has its own switch, to break the live connection, so you must not pull the plug each time as in Europe....

All new houses and a lot where heavy renovation will or has taken place (and people with some sense live!) have an ELCB installed as part of the main breaker for the house....

....and still people manage to kill themselves, but it is quite a bit more difficult than in Germany for instance....

The EU wanted Britain to change to the Continental version, we told them it would be better if they changed to ours.......!

See this URL for a coverage of world standards in this area....

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

?

As indicated by your last comment, it would appear that you have seemingly not understood what has been already said.

Do not see this as being negative, but it might therefore be a good idea to take this as a possible sign for you not to get physically involved in this area of competence....or its a language/understanding problem, I cannot from my point of view say exactly which....

Have a great day.

Samak, Shukaran, enta quious allium?

December 06" I was sailing as first assistant engineer on a ship that delivered components to a Red Sea port for an Ammonia plant.

Due to an error by the electrician the ship went aground while transiting the canal southbound. Sure put the cat amongst the pigeons!

Regards CEKM

Funny thing that, it is amazing how many mistakes electricians make, mind you I would not like their job on some of these more modern ships.

Says he, who has never made a mistake. Ha ha ha.............one could only wish!!!!

Not long ago an electrician on a foreign vessel electrocuted himself changing fluros in the engine room of the vessel. COMPLACENCY is deadly.