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-   -   Difference between Phase, neutral and ground in AC (http://www.physicsforums.com/showthread.php?t=311702)

neo_star May4-09 12:07 PM

Difference between Phase, neutral and ground in AC
 
I am having a little confusion about the difference between neutral and ground because certainly one can touch a neutral wire and never get a shock. What is neutral any way is it neutral, 0 volts.

Then while handling electronics we only use DC. Now in DC there are 3 things
1.Positive(+) or supply
2.Ground
3.negative(-).

we normally use positive and negative then what is ground for.....?

Dadface May4-09 12:22 PM

Re: Difference between Phase, neutral and ground in AC
 
Quote:

Quote by neo_star (Post 2184788)
I am having a little confusion about the difference between neutral and ground because certainly one can touch a neutral wire and never get a shock. What is neutral any way is it neutral, 0 volts.

Then while handling electronics we only use DC. Now in DC there are 3 things
1.Positive(+) or supply
2.Ground
3.negative(-).

we normally use positive and negative then what is ground for.....?

For safety.Should a fault develop and an exposed metal part which is grounded reach a high voltage a large current will flow to ground and this will blow the fuse or pop the circuit breaker..

waht May4-09 04:29 PM

Re: Difference between Phase, neutral and ground in AC
 
Ground is usually earth. You can tie ground and negative(-) together to insure that you are referenced to your surroundings. If for instance, the power supply wasn't grounded to earth, then it's possible that a potential difference between the power supply and ground could develop to the point of damaging it's circuits or at worst shock you.

dmd4raj May8-09 07:25 AM

Re: Difference between Phase, neutral and ground in AC
 
there is no ground in AC Signal.only Phase and neutral.Ground refer neutral.....only in DC +,_ and ground....

russ_watters May8-09 11:55 AM

Re: Difference between Phase, neutral and ground in AC
 
That isn't true. There are many configurations of AC power that include a ground wire and the ground wire is literally tied to the ground. Now often the ground and neutral are linked at a panel or transformer, but it is still there - there is still a separate wire for it from the panel to the load.

Dr.kW May9-09 09:41 PM

Re: Difference between Phase, neutral and ground in AC
 
a little more...
(dc ckts) Neutral is midpoint between a positive and a negative. Relative to ground, the potential differnce is usually zero, but that is not necessarily true. In power electronics, it may be true only on average, such as in some switched-mode power supplies where the neutral voltage bounces above and below zero, but is zero on average.

Ground is generally 'earth' or equipment frame or chassis or building iron or a ground rod driven into the ground, and is usually associated with the human safety side of the electrical system. Neutral and ground may be directly connected, or may be connected with an intentional impedance between them (search on 'high resistance grounding'). For these circuits, under normal conditions there is no potential difference between neutral and ground.

The key is what happens when there is a fault, where part of the live circuit gets connected to the frame. If left unchnaged, there is a shock hazard. By having the frame electrically connected between its own parts and bonded to the grounding circuit ensures a current path to the power supply, which then ensures the fault protective system (e.g. circuit breaker) recognizes the problem (such as sudden high current) and disconnects the circuit. A resitance between neutral and ground can be used to detect current even when low, hence still sense a fault.

I hope this helps.

darkwood Jun13-09 11:16 AM

Re: Difference between Phase, neutral and ground in AC
 
In britain (as i cant speak for other countries electrical networks) the ac supply comes into your house as a single phase(live) but the neutral is either seperate or combined with the earth to the point of the electric boards cutout, thereafter it must be seperate for safety reasons, up to this point it is only different by size and markings or in the combined state not at all.
The power grid goes through a step down transformer to reduce the high voltage the electricity is carried with but because of the way a/c is generated it is still in the form of 3phases and no neutral, to create a neutral the step down transformer has a center tapping made at its star point this is then used as combined neutral earth or a second tapping is taken for a seperate earth.

turbo Jun13-09 11:36 AM

Re: Difference between Phase, neutral and ground in AC
 
In the US, power comes to your house from a transformer at the street. The transformer steps down the high voltage at the street to about 240V and the transformer's secondary coil is center-tapped. This center-tap forms the neutral leg of the AC circuit and the two end-taps are tied to the two "legs" of the AC circuits at the breaker-box, supplying ~120V to either leg. At the breaker-box (actually at the supply-box) there is a hard ground reference made to a metal probe driven into the ground (earth) and the neutral in your house is referenced to that. If you will look at a common grounded 120V receptacle you will see a couple of screws on the right (as seen from the front) where the "hot" wires can be connected (there are two screws so that you can chain from one receptacle to another) and on the left, there are two screws for "neutral" and one (often tinted green) for the ground connection.

The two "hot" legs are out-of-phase with each other (being taken from the end-taps of the transformer's secondary coil). Often, instead of running power through a single leg and neutral, power will be run across both legs, yielding a full 240V potential. This is most often done when high power is required, as in an electric oven, clothes dryer, well pump, high-capacity air conditioner, etc.

josh25w Jan24-11 09:03 PM

Re: Difference between Phase, neutral and ground in AC
 
In a three phase AC power system, the purpose of the neutral is to carry the inbalance load of the energized conductors back to the source. If the system is completely blanced then there is no current on the neutral. There is no electrical pressure applied therefore no shock. On a single phase system, since there is no possibility of balance between the phases, the neutral provides the total return path back to the source.

Averagesupernova Jan25-11 09:38 AM

Re: Difference between Phase, neutral and ground in AC
 
Quote:

Quote by josh25w (Post 3101326)
On a single phase system, since there is no possibility of balance between the phases, the neutral provides the total return path back to the source.

-
Ummmm, no. In a split-phase 240/120 volt system in a U.S. residence if the two hot legs are carrying the same current and are both carrying the same type of load (non-inductive for instance) then the neutral will not be carrying any current.
-
Bad enough you misinform, but why dig up a thread last posted in over a year and a half ago?

darkwood Jan26-11 03:32 PM

Re: Difference between Phase, neutral and ground in AC
 
Quote:

Quote by Averagesupernova (Post 3102081)
-
Ummmm, no. In a split-phase 240/120 volt system in a U.S. residence if the two hot legs are carrying the same current and are both carrying the same type of load (non-inductive for instance) then the neutral will not be carrying any current.
-
Bad enough you misinform, but why dig up a thread last posted in over a year and a half ago?

I must agree this is an old post hence my amusment when my email notified me but you may have misunderstood him as 'single phase' in itself here in uk means 1 phase with neutral which is 230v and not split phase... 2 or 3phases here would be 400v so i see you are both correct in your answers but your terminology may differ' depending on your location, its a niggle of the forum that it dosn't express users country of origin under their user name, it would clear up alot of confusion.

josh25w Jan26-11 07:03 PM

Re: Difference between Phase, neutral and ground in AC
 
I am so sorry that I offended you. It sounds like you lost a few hours of sleep over the whole ordeal. I should have been more specific. What I was referring to was on the distribution side. A single phase circuit would include just one primary (energized conductor) and the neutral in a wye configuration. Therefore, the neutral would carry the return path to the source. I didn't think anyone would get so upset that I didn't put my example into a format that they are familiar with. So sorry.


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