please tell me the difference between the two

 

It can be stated that Neutral can be grounded, but Ground is not neutral.

A Neutral represents a reference point within an electrical distribution system. Conductors connected to this reference point (Neutral) should, normally, be non current carrying conductors, sized to handle momentary faults (short circuits) occurring in electrical equipment. However, with the introduction of non linear loads, such as computers, electronic lighting, TVs, VCRs and other switchmode power conversion equipment, the requirements for the neutral conductor has changed (increased).

A Ground represents an electrical path, normally designed to carry fault current when a insulation breakdown occurs within electrical equipment. (Note: Breakdowns can be forced by connecting (dropping) a metal tool or conductive material from a voltage potential to the steel structure within a facility.) Connections to the electrical path (Ground) are made convenient for the installation of electrical equipment. Some current will always flow through the ground path. This current will come from a number of normal sources. Capacitive coupling and Inductive coupling between power conductors and the ground path (conductive conduit, conductive structure members, etc) are the greatest sources of ground path current.

Source: http://www.ab.com/drives/techpapers/rfignds.htm

also http://en.wikipedia.org/wiki/Neutral_wire is good

 

Scubasteve,
I have exceptions with your post.

In a "normal" AC service, the neutral provides the return path for current on the 120v sides, and has no function for 240v appliances.

"Ground" should never have any current on it. If there is more than a few mA current on a "ground" wire, there is a problem.

The purpose of the Neutral wire is a power return path.

The purpose of the Ground wire is for operator safety.

At the electrical service panel, Neutral and Ground are connected together. This must be the only place that they meet, or the premise of human safety is violated.

No, I'm not an electrician. However, this is a very important issue. I hope that someone who IS a licensed electrician will respond to this thread, and confirm or correct my assertion.

 

Well, I actually just copied and pasted from that website to make it easy, which I stated the source. I'm glad I am not under the Wookie-glass !

Steve

 

I'm licensed in Oregon and Washington and am a member of IBEW Local 48.

The notion of neutral and ground is indeed a confusing one, primarily because of unfortunate terminology.

First, a word to all those who oppose the phrase "current flow:" Buzz off! I am not going to further complicate this SAFETY issue with the phrase "charge flow." The terms "current" and "charge flow" and "current flow" all mean the same thing. If you don't like it, stop reading NOW.


"Current carrying" does not mean the same thing as "conducting." "Current carrying" is more like "hot" or "switched hot" or "traveler." Current does absolutely flow through the neutral, even though the neutral is not a "current carrying" conductor.

Under normal conditions, no current flows through the ground wire. Under certain fault conditions, current does flow through the ground wire - instead of where we don't want it.

The neutral is the grounded conductor, whereas the ground is the grounding conductor.

 

sir i could understand sgt wookies' and scubasteve's thread. it is very interesting and thanks for the information. but thingmaker sir thread is really some thing vague

 

Depends where in the world you are.

Most mains AC electrical supply these days is three phase to the local substation. This may be a transformer on a pole near you supplying overhead cables or a transformer in a compound, with underground cables.

Three phase means that the are effectively three elctricity supplies on three separate cables.
As you know, with AC the voltage varies periodically, rising and falling with time.
The three phases are carefully controlled so that when one is rising another is falling.

On any individual phase once the current has passed through your load it is returned by your neutral connection to the substation.

Here the magic occurs, because the rises and falls in the different phases are at different times they nearly cancel each other out, leaving only a small imbalance current.

This is fed to earth at the substation.

Your neutral should not be earthed at your local distribution board as this nullifies the whole cleverness of the scheme and throws the phases into imbalance.

Steve and Wookie.

The average voltage between the phase conductor and the neutral is 230 volts standard in Europe and 120 volts standard in North America.

The voltage between any two phases is 240 volts in North America and 415 volts in Europe. So beware of suggesting that the neutral at 240 volts has no function.

The clever part of balancing the return current of one phase against another is that it substantially reduces the cabling requirement for electricity distribution.
Two common schemes are for one phase to feed alternate houses or one side of a street and another phase to feed the remainder. The third phase is used for street lighting etc.
On average the currents and thus the return currents will be very similar in each phase.

Heavy duty (industrial) equipment receives the extra oomph provided by all three phases.

 

interesting...

 

The average voltage between the phase conductor and the neutral is 230 volts standard in Europe and 120 volts standard in North America.

The voltage between any two phases is 240 volts in North America and 415 volts in Europe. So beware of suggesting that the neutral at 240 volts has no function.

I'm not conversant with European power distribution, but American residential power is split single phase, not three phase. That's 240 between the hot leads and 120 from either hot lead to ground. American residential hot leads have current 180 degrees apart, not 120 degrees as is found in 3-phase.

 

I do believe that the US has many local generating sets, especially in rural areas.
These can be of all sorts of types.

This situation is also typical in many other parts of the globe especially where population density is low.

In the UK we have centralised power stations and a distribution grid. I think they use 3 phase also because 3 is the smallest number you can connect in star - delta formation. You cannot do this with two phase systems. However the principal of load balancing on polyphase systems still holds good.

 

Yes in the USA transmission lines are indeed 3 phase, as most of the world is, it's the best way to do it.

Theres no magic at the substations only transformers, usualy the 3 phase is stepped down to a lower voltage 3 phase and sent out as 3 phase to the neighborhoods on local poles or underground, its at your nearby pole that 1 of the 3 phases is chosen, and transformed to the needed voltage, here in the states 120/240, still no magic is actually used.

In rual areas often you will find single phase overhead if no customers require 3 phase (you can tell by only 2 wires from pole to pole).

Rick

 

Interesting. I just picked up on this earlier today.

A couple of days ago, we lost power completely from around 11am until nearly 9pm.

After driving around a bit, I discovered a power line down; it had parted between poles, and was draped over a barbed-wire fence.

We live on the edge of a rural area. There are high-tension wires and neighborhood distribution lines along roads. But the high tension wires are far above the ground; perhaps 100' or more - the wires are in groups of three; indicating to me that they're from a three phase delta transformer.

But the neighborhood distribution wires were different; there were three in a group, and then a fourth further down. The group of three wires had much larger insulators than the fourth wire. I initially thought that the 4th wire was perhaps a cable to maintain tension between the poles; but now I'm thinking that this 4th wire is a neutral line from a wye transformer secondary.

The neutral wire (the 4th one down) is the one that parted. it looked burned; it had contacted a pine tree which also looked burned; the one end that was sticking up appeared to have melted. (a bit hard to tell, I stayed a good couple meters away from it.)

It took the power company six hours to get around to repairing it.

 

Yes the neutral would be the fourth wire, this would be a wye system, have you never seen the neutral hot?

If the neutral gets cut, in this case because its 3 phase all the unbalanced loads will backfeed through the cut neutral, this is the number 1 killer of electricians, never believe the neutral isn't hot.

What you saw was probably 13,000 volts or more, unfused doing its deed, you were wise to keep away.

Rick

 

Actually, I'd not seen power lines down that I can remember since I was a teenager. That was quite a while ago.

While I've seen some minor voltages on the neutral on my own residential service, I don't make a habit out of checking it, nor other residences. I'm not an electrician. I usually don't start looking at things unless I notice there's a problem.

I'm not a complete stranger to high power/high voltage circuits. 18.5kV @10kW can do a lot of damage if one isn't careful. But like I said - I'm not an electrician. I'll add "not a linesman either" to that disclaimer.

It wreaked havok at my house. The Klondike bars melted. Should've eaten them as soon as the power went off.

 

Theres no magic at the substations

Formal definitions generally do not promote understanding. Often a loose and chatty explanation does this. The inquirer can then return to the formal with renewed vision.

I was merely trying to emphasise a sound (clever) piece of engineering taking advantage of the fact that in a perfectly balanced multiphase system no neutral is actually necessary.

Terminology differences are also a difficulty. I used star - delta whereas I note some use wye - delta. I have also seen star - mesh used (Rosen).

 

Oh Wookie, to bad about the Klondikes.

Studiot, I'm sorry, sometimes I get carried away, you can smack me up side the head, I'm only a junior member after all.

 

I have a doubt..
In case of a ungrounded neutral System, why do we have the charging currents flowing into the ground,when we don't have the phase voltages with respect to the ground?

 

 

The thread starter opened this thread 7 years ago and only has one post to his name.

 

I have a doubt..
In case of a ungrounded neutral System, why do we have the charging currents flowing into the ground,when we don't have the phase voltages with respect to the ground?

As already noted, you are replying to a seven year old thread in which the thread starter has never posted since.

If you have a question related to this, please start a new thread so that the responses will be in response to your query and can better server your needs.