Does The Neutral Line Carry Current?

It is very basic Q; Any how First I welcome you to CR4. My answer is: your 3 - phase - 4 - wire system is unblanced. Hence balancing is you prime job as quickly as possible.

Even though the distribution can be perfectly balanced across the three lines, balanced utilisation of the loads so distributed cannot be guaranteed. Hence, there WILL be neutral current, even in a perfectly balanced distributed system.

In = √((Ia²+Ib²+Ic²)-((Ia*Ib)+(Ia*Ic)+(Ib*Ic)))

Balance the loads as best you can!

Also, if the electrical loads introduce harmonics into the system, you may have significant neutral current even when line currents are apparently balanced.

You should assume that neutral conductors ALWAYS carry current because systems are never 100% balanced.

Part of the reason there are four conductors for a three phase line is that it is extremely rare that the circuits will be balanced. Unless you are a major user in the over all system, you may not be able to contribute much towards the total system balance. Depending on the user network, the imbalance may go though a daily cycle and the average balance is satisfactory, but the balance at any given time is not. Your electrical supplier may be able to help you if this amount of imbalance affects your system negatively.

The supplier has no control over the balance of the user's system.

There is seldom only one user on a system. If you are a big enough user you might be. I agree that the user can influence the balance. But if he did not know current flows in a neutral line, he will need help understanding how to balance his load. The supplier can tell him whether he is a big enough fish to make any real difference.

GA

The first really "good" post reading down from the top.

None of the others helped the OP in anyway.......

The OP is his own worst enemy as he did not mention whether he had 3 phases or 2 "phase" US style or single phase.......

Not only unbalanced load current that causes neutral Current ,but also the presence of triplen harmonics in the load current.If the predominant loads are either arc furnaces,or Thyristor controlled drives,then there is more possibility of harmonics and consequent harmonic current,

Further to PWSlack's comments, you must mainatain neutral conductor in "Nuetral" condition by not allowing any huge currents to flow through.

It depends "where" you mean, in a single phase circuit, the neutral (should!) carry the same current as the phase.

But when you get back to the DB, the neutral link should theoretically be at zero current, in the wire going back to the substation in a perfect world.

Generally though, the currents are not balanced exactly where single phase loads are in use....most housing for example has single phase loads.....the neutral point will have some voltage on it......unless you live where there is no ground supplied by the electric company and the ground is only connected to neutral in each house, for that house alone. Then it will be impossible to measure easily.....as ground and neutral will be the same....

Measuring between ground and neutral as far away from the DB may show a difference.......measuring between the water piping (assuming copper or steel) to ground and neutral may show something when the bonding is removed for the test......what use this is a normal situation is a good question........

Yes! Three phases must be balanced at the nearest UVW-N junction box possible.

Not knowing what UVW-N means, precludes an answer...

Phases R/Y/B - N; some designate UVW/ RST.

Then I don't agree with your post.

Its a "nice to have", but what is the problem when you don't have it. The local substation has the neutral/earth link in most cities......

Only where 4 wire supplies are in usage is the link in the house/building.

In the UK for example, few houses have 3 phase at all, they get a single phase, a neutral and earth/ground fed into the house.......that means the link is in the substation and therefore substantial currents flow in the neutral, all the time, till somewhere in or around the substation - assuming reasonably balanced loads......

I agree with your point. It is same in India also. In house hold it very difficult to balance. I am talking about Industrial supply. In industries also due to single phase loads, SMPSs, etc 3-phase system get unbalanced. In that case instead of trying to balance the at sub-station level it is recommended to balance at nearest junction box or at distribution boards. In India government supply electricity through independent Local Electricity Boards. Electricity boards are due to power generation shortage, forced to impose power cuts to Farmers using pump sets at the same time provide lighting power. Here in India the local electricity boards giving one single phase through all the 3 wires to one village and other phases to some other village thus preventing formers using 3 phase pump sets. This also leading to 3 phase unbalance and high neutral currents.

Codswallop.

"...only flowing in the opposite direction."

Are you sure? If so, how can work be done? This implies net zero current at all times through the load, be it a motor or whatever. Unconfuse me.

Its not true,.

The "leg in question, where the load is higher, the actual "neutral point" will have moved up into that leg, so measuring the physical neutral point, it will have a few volts on it....

I would expect that there are regulations to keep this voltage difference within a certain level, but I have not seen the regs personally.....

I guess what I was getting at is: the neutral line is the "return" from the load -- meaning it completes the circuit. So any instantaneous voltage reading in "neutral" line would be the same as reading in the phase or "hot" side. And current would be in the same direction when considering the completed circuit. I think the "opposite" direction was meant to convey that the current in the phase line is toward the load, whereas the current in the neutral, or return line is away from the load. But the current is the same direction when viewed from the phase side of the source to the return side of the source.

Total and utter rubbish, unless you live where DC instead of AC is used...even then most of it will still be rubbish......

May I recommend completion of an "AC 101" course or similar as a requirement if you want to be able to discuss AC here and not get jumped on each and every time (we all know who you really are, its rather obvious!!) for your inane comments......enough is enough for most people, but if you like being the butt of our jokes and you do keep us laughing I must admit, then stay as uneducated as you are....... I do like a great laugh to start each day........

But if you want to really know more then firstly do not forget that the current and the voltage REVERSE every 100th or 120th of a second, depending upon the type of AC supply you have where you live......at one point of the cycle the electrons will flow from the phase to neutral, in the other half of the cycle they will be reversed and flow from neutral to phase. THIS IS HOW AC WORKS - ALWAYS!!!

Here are some websites that could improve your understanding of AC:-

http://www.electronicstheory.com/html/e101-26.htm

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

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

There are plenty of such sites around, this is only a small selection but you need to start somewhere.....

Please also remember that with correct "bonding", the neutral will be referenced to earth, or at least it should be, that is, when measuring between neutral and earth you should see close to zero volts, if not exactly zero AC volts.

The voltage, if any, measured will reflect both the load balance or not of the phases, the load drawn and the distance to the earth neutral bonding point.

Between either earth or neutral and phase, you will measure the line voltage, probably around 110 or 220 volts depending upon your location in the world and whether you are close to the substation, then slightly more than that will be measured!).

Sorry to touch some nerve. I don't think I misunderstand AC... I've had a career in electronics for 40 years. I remember most of the "AC" theory. I think this is just cross-communications.

If you consider the neutral line to be nominally at 0V, then you could even argue that there is no current. But that would be incorrect. To test that, you can loosen the neutral wire and use yourself as a bridge to complete the circuit.

Additionally, if you could freeze the current and have electron flow tagged with directional arrows and you could enter the wire and walk the complete circuit from H to N, the frozen "flow" would always be the same direction from that reference point. (See the diagrams under the paragraph "Adding a 120V Load" at this link.) Now trace the current flow arrows from L2 through LOAD 1 and back to N at the source. Maybe I need new glasses, but the arrows are all in the same direction from what I can see. I will admit that the arrows are small enough on my monitor that I can't tell whether the N arrows are green or blue. I was speaking of single phase. I thought I made that clear.

Mains AC is not electronics......you have proved this significantly in the last few posts, well done!!

If you start working on mains AC at some point, about 5 minutes later you will either be dead or on your way to Hospital.

I am not even going to bother to to start to tell you what was wrong in your last post.

I leave you to your own self made destiny, bye!!

Codswallop.

Codswallop.