Neutral Point

arunbabu; for what reason? perry

I beg to differ from your reasoning about following local codes.

The question here is about NEUtral in a transformer and in an electric motor. Answers given by other people are straight forward and to the point.

I agree that it does not matter how a motor's Neutral if any is wired. What is important is That Transformer's neutral is connected to ground.

There should not be silly ways to wire a circuit orherwise Electric Hazard will ensue.

As a code consultant on the subject, I will just say that all the codes are there to prevent HAZARDS and ensure safety of the personnel.

I hope this answers your question Mr BABU. Let us get the feedback.

Thakral raj

So you're a code consultant and you seem to think that local codes do not have to be followed. Now we all have had bad days at work, but every time I felt that my job was completely pointless I quit. There most certainly are many silly ways to wire a circuit that can kill people. If it was impossible to build a circuit badly, we wouldn't need wiring codes at all then and you would be out of a job. (Maybe you should be.)

I'm very suspect of anybody that comes to a public forum that effectively says "I don't know what I'm doing. Here's the least amount of information I can give you. Help me do my job so others don't get hurt." (arunbaba my apologies, I'm exaggerating here to make my point.) To this request I will always answer that somebody qualified and authorized to decide what needs to be done, must look at your system and decide. People looking at a few lines of text from anywhere on this planet should not provide an answer that may have nothing to do with the actual situation.

In this case, I have no idea how many power sources exist in this system. I have no idea the inertia this motor will be driving. (Anybody here think that a motor cannot be made into a generator?) I certainly have no idea if the motor's neutral connection is permanently assembled to connect to the chassis. I do not know what is meant by a ground here. I also have no idea if this motor is used as a train engine, aileron servo motor, vacuum pump, sewage pump, breast pump, deck winch or a Prius motor. So I will not say that anyone here has properly answered a potentially lethal question. I refuse.

I wish you well in your job and like you rightly said should be out of a job.

You think this is justified to speak such things in a " public forum'

Good luck in your job and God bless you and thanks for adding to growing unemployment.

Neverthless, the simple question has been so distorted that the real sense cannot come out of all these arguments.

I would read this simple english in this simple question and answer it, rather than show off your knowledge that you can ask so many other Questions.

Code should not be brought unnecessarily. A qualified electrician at the site can give the best simple answer. But I will still insist that NEuTRAL is a NEUTRAL in all countries except their language may call it differently. Grounding and Earthing is the same on this planet we call EARTH.

Mr Babu the neutral is generally connected to earth at the transformer only so that the shifting of neutral due to load un balance can be taken care. There is no point or effect if you connect the neutral of the motor to earth. It matters nothing .

The Neutral of a Supply transformer is connected to earth to permit / allow a return path for any fault occuring within the load circuits, to ground/earth. Any protection devices to protect against such faults will need that path to operate properly.

If you connect any type of motor or any part of the load to the ground you are supposed to trigger the protection devices that will disconnect the load from the supply.

3 phase motors do not have neutrals (or at least the suply neutral wire) connected to them. In Start connection, the start point is referred to as the neutral point since the windings are supposed to be balanced and that point will become an artificial neutral to be kept as such (isolated from ground).

no,

The neutral of a star connected motor is not connected to anything because the motor is a balanced 3-phase load in which the sum of the three phase currents is zero

First off the neutral by definition is the identified grounded conductor. So in order to have a neutral you must have a grounding point first. The reason for a neutral is to have a safe return of the current to the location from which it was derived. Second it establishes a point of reference from where we can get a trip of an overcurrent device in the event of a short to ground in a given circuit or piece of machinery.

As it was stated before, what would be the point of have a neutral install in a motor winding?

It is system grounding.As such single point grounding is preferred.The largest equipment and continuously on condition which is usually the mains transformer is used for grounding since if it is disconnected the loads will be disconnected.Multiple grounding such as lt motor neutrals is not a good practice.

If the mains trafo winding is delta on the load side the grounding may maintained by the generator neutral grounding.Then if the generator is switched off , to maintain the system grounding ,neutral of a motor may temporarily grounded.

Like any power system topic this is also an involved one and much consideration will be required for safety,proper operation of protections and communication integrity.

The star point of the motor winding needs to be connected to the neutral conductor, if a neutral conductor is provided. If there is no neutral conductor, then there is nothing to connect the star point to, and therefore no need to connect it to anything.

The ground/earth connection of the motor needs to be connected to the local ground/earth system.

If in doubt, consult a qualified electrician.

multiple intentional grounding is very rare and must be done with great care if at all attempted.If the system is always having same configuration perhaps it may be applicable.otherwise the system zero sequence impedance may fluctuate over wide limits besides the prospect of circulating currents.many systems are working with improper neutral grounding but if a contingency arises the consequences could be very drastic if the system is large.on small systems,lt,perhaps a wrong practice may not result in drastic consequence but better keep in mind time tested fundamentals.

The simple answer is you can, there is no wrong in doing so. Such as the motor manufacturer states that you must connect the neutral point to ground. But if none, it is much better if you just leave the neutral point isolated from grounding system, even in a multiground system, except for the chassis ground which you MUST connect it. The advantage of not connecting the neutral point to the ground is you can always monitor the ground insulation of your motor winding by using permanently connected IR meter (insulation resistance meter). IR meter is very important scheme to apply because it will always give you a rightful health of your winding insulation 24 hrs a day.

Mr. Babu & friends,

The grounding/earthing of the neutral point of a transformer star winding is to establish, as others have said, a route for fault currents to return to the power source. This allows proper operation of protective devices such as fuses or circuit breakers. Downstream from this connection point, I would strongly recommend against any other connection of a circuit conductor to ground.

In your question, it is correct to assume that the star point of a star-connected motor is at the same voltage as the grounded neutral point of the service. However, that assumption can easily and frequently be wrong. Any connected load that causes an unequal current flow in the conductors will shift this star point away from the transformer's neutral point. If you have grounded the motor's star point, this will cause current to flow from through the grounding path. In addition, the voltages across the windings will now be unbalanced. This will in turn create unintended circulating magnetic fields in the motor and cause unnecessary overheating.

You now have at least 4 good reasons for NOT earthing/grounding the star point in a motor:

1. This makes future insulation resistance tests of the motor windings or feeders impossible. (Mentioned by at least one other post.)
2. It causes unwanted currents to flow through the ground (a violation of many electrical codes).
3. It probably will unbalance the voltages in the winding, and overheat the motor.
4. It is impossible to do with a 3-lead star-connected motor and is not in compliance with the motor manufacturer's wiring instructions. (Valid, but not discussed above.)

--John M.

Grounding helps easy detection of earth faults.True.With sophisticated numerical relays it is not impossible to selectively detect earth faults in ungrounded systems as well.The most important reason appears to be to get a ground reference for the circuit with definite impedance.Ungrounded system will have a huge zero sequence impedance as such if a transient appears on the hv side it will get coupled to lv and the impressed voltage is some what proportional to grounding impedance.

Motor star point grounding will circulate unbalance currents and with the neutral conductor acting as an antenna this could give rise to communication interference as well.