Purpose of the neutral

[Lectricbota]

It seems to be a Code requirement.

Well, yeah that too.

But a neutral conductor in most instances is a current carrying conductor under normal conditions.

A ground is just a bonding of equipment (that might become energized in abnormal/fault conditions )for creating a low impedance path back to the source to assist in clearing faults.

 

[GoldDigger]

I would have to do more research to get a better idea of the evolution of the use of the word neutral.

As a fully self-licensed folk etymologist, I favor the argument that "neutral" arose from its meaning of unaffiliated, not favoring one side or the other (e.g. Switzerland), and originates from its position equally distant from all of the phase wires/voltages. This applies equally well to split-phase, two phase (four phase?) and three phase circuits.

 

[Strathead]

Well, yeah that too.

But a neutral conductor in most instances is a current carrying conductor under normal conditions.

A ground is just a bonding of equipment (that might become energized in abnormal/fault conditions )for creating a low impedance path back to the source to assist in clearing faults.

Now you have to be careful. "current carrying conductor" has a code meaning. As such, a neutral is, in fact, NOT a current carrying conductor when it is part of a multiwire branch circuit, carrying only the unbalanced current between phases. So, to claim that in most instances it is, is probably not statistically accurate.


Just saying...:angel:

 

[Lectricbota]

Now you have to be careful. "current carrying conductor" has a code meaning. As such, a neutral is, in fact, NOT a current carrying conductor when it is part of a multiwire branch circuit, carrying only the unbalanced current between phases. So, to claim that in most instances it is, is probably not statistically accurate.


Just saying...:angel:

The definition defines NEUTRAL CONDUCTOR The conductor connected to the neutral point of a system that is intended to carry current under normal conditions

Having said that I get what you are saying--I just mostly work with 120/208 wye systems so maybe i get tunnel vision sometimes

 

[Strathead]

The definition defines NEUTRAL CONDUCTOR The conductor connected to the neutral point of a system that is intended to carry current under normal conditions

Having said that I get what you are saying--I just mostly work with 120/208 wye systems so maybe i get tunnel vision sometimes

But the code has a specific meaning for a current carrying conductor, and that is not it. We are pretty meticulous here sometimes, (some would say anal hmy That is all I was saying.

 

[kwired]

But the code has a specific meaning for a current carrying conductor, and that is not it. We are pretty meticulous here sometimes, (some would say anal hmy That is all I was saying.

Not true.

310.15(B)(5)(a):

(5) Neutral Conductor.

(a)

A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(3)(a).

It just says the neutral that carries only unbalanced current does not have to be considered a current carrying conductor for the purpose of ampacity adjustments for more than three current carrying conductors in a raceway.

There is no definition of current carrying conductor in art 100.

 

[eHunter]

There is a definition of a neutral conductor in Article 100.
"Neutral Conductor. The conductor connected to the neutral
point of a system that is intended to carry current under
normal conditions."

 

[kwired]

There is a definition of a neutral conductor in Article 100.
"Neutral Conductor. The conductor connected to the neutral
point of a system that is intended to carry current under
normal conditions."

This was pointed out already in post #24.

 

[Flux]

Let?s answer this question short and sweet.
A neutral is a conductor is used to get 277 volts out of the for mentioned 3ph 48OV system you mentioned earlier
where the neutral is tapped to the XO or center tap on a transformer at the separably derived system it is not needed unless the mechanical equipment
you are using uses 277V your equipment would most likely have a control transformer eliminating the need for 277V. The bond should only
be in the system transformer to bond the transformer center tap hence referencing ground so your overcurrent devices work if it is bonded else where
the equipment ground becomes a conductor (danger). You always have an equipment ground (i.e. bonding metal bits)
this is to provide a path for the electricity to follow back to the overcurrent device enabling it to work
whether or not your equipment requires a neutral or not.:thumbsup:

 

[kwired]

Let?s answer this question short and sweet.
A neutral is a conductor is used to get 277 volts out of the for mentioned 3ph 48OV system you mentioned earlier
where the neutral is tapped to the XO or center tap on a transformer at the separably derived system it is not needed unless the mechanical equipment
you are using uses 277V your equipment would most likely have a control transformer eliminating the need for 277V. The bond should only
be in the system transformer to bond the transformer center tap hence referencing ground so your overcurrent devices work if it is bonded else where
the equipment ground becomes a conductor (danger). You always have an equipment ground (i.e. bonding metal bits)
this is to provide a path for the electricity to follow back to the overcurrent device enabling it to work
whether or not your equipment requires a neutral or not.:thumbsup:

I don't know if that is short and sweet or not.

The neutral is a point on the system that in the case of a wye connected transformer exists even if the phase to neutral voltage is not needed. You can ground any point of the system and have a grounded conductor, you just can not ground more than one point or you will have a fault. NEC in general requires the neutral conductor, if one exists, to be the conductor that is grounded for grounded systems.

If you have a 3 wire delta system or a simple 2 wire single phase source you have no "neutral". To ground either of these systems you can pick any point and ground it. That point is still not a "neutral" but is now a "grounded conductor".

Most common "neutrals" are for 277 volts or 120 volts and equipment is designed to operate at these voltages mainly because those voltages naturally exist within the associated systems. There are advantages as well as disadvantages to using line to neutral loads. Seems as though lower voltage is maybe the main reason for so much 120 volt equipment, but along with using grounded conductor for carrying current comes the risk of placing stray voltages and currents on other grounded objects, either if things are done incorrectly or if something should fail.

 

[Flux]

kwired does not the single phase two wire can transformer have to reference ground it is not a delta system in an industrial applications that is monitored with a light between ground and a phase to alert the monitor that there is a ground fault before the second connection to ground has a chance to happen. I don't think it would be within code to bond your grounded conductor (new term) to ground anywhere just at the first means of disconnect or at a separately derived system or transformer.

 

[kwired]

kwired does not the single phase two wire can transformer have to reference ground it is not a delta system in an industrial applications that is monitored with a light between ground and a phase to alert the monitor that there is a ground fault before the second connection to ground has a chance to happen. I don't think it would be within code to bond your grounded conductor (new term) to ground anywhere just at the first means of disconnect or at a separately derived system or transformer.

What you need to understand is nothing is grounded until you actually connect it to ground. A simple single phase 120/240 is just that. The center tap has no ground reference until it is connected to ground or at least a conductor that is connected to ground somewhere. NEC requires that this center tap will be the conductor you connect to ground in virtually all cases, but NEC does not govern the laws of physics. Should you ground line 1 instead of the neutral then you do not have a short circuit like some believe you will. You just have a zero ground reference on line 1 instead of the neutral. Line 1 will still have 120 volts to neutral and 240 volts to line 2. In this same install line 1 has zero to ground, neutral has 120 to ground and line 2 has 240 to ground.

With a single phase two wire source you have to pick one conductor and ground it (to have a grounded system). Doesn't matter which one.

With a three wire delta the same. Pick one phase conductor and ground it. Industry standard is B phase, but what is B phase? Kind of depends on which one you decide is A phase I guess. Once you pick one and ground it, it becomes B phase.

Same with a wye system. The neutral is not automatically grounded, someone has to make the bond at some point. Some cases that may happen when manufactured, but is intentionally done. Most dry type transformers the bond is done in the field. If you bond the wrong conductor in the field it doesn't blow up, you just have the ground reference in a different place.

The industrial ungrounded delta system is no different than a corner grounded system except it is not grounded.
There is also a high impedance grounding system used for similar purposes for wye systems. They basically monitor the neutral current to determine if something has a ground fault. Once this happens there is indication there is a fault but nothing shuts down giving operators a chance to shut down a complex process in an orderly fashion instead of just having it crash because a fuse or breaker opened. Should a second ground fault occur it will open fuses or breakers though. You can't use the neutral for things like 277 volt lighting on this system because of the high impedance in the neutral.

 

[Smart $]

... You can't use the neutral for things like 277 volt lighting on this system because of the high impedance in the neutral.

Man, I hate to throw a wrench into your well-oiled machine here (), but the neutral itself has no significant impedance. The high impedance is only in the neutral-to-ground resistor (the usual means for high-impedance grounding). But you are correct in that part of the requirement for using a high-impedance grounded neutral system is that it serve no line-to-neutral loads.

 

[kwired]

Man, I hate to throw a wrench into your well-oiled machine here (), but the neutral itself has no significant impedance. The high impedance is only in the neutral-to-ground resistor (the usual means for high-impedance grounding). But you are correct in that part of the requirement for using a high-impedance grounded neutral system is that it serve no line-to-neutral loads.

Ok to be correct I should have stated something like "because of the impedance inserted in the neutral". Which is basically what I meant. Why can't you listen to what I mean instead of what I actually say?

 

[Smart $]

Ok to be correct I should have stated something like "because of the impedance inserted in the neutral". Which is basically what I meant. Why can't you listen to what I mean instead of what I actually say?

I was listening to what you mean... didn't hear it. There must have been some brain wave interference. Or you were directing at Ohio and I'm in Alabama

 

[liquidtite]

For balanced loads on split or three phase supplies, a neutral is sometimes not required and even when it is there it (ideally) does not carry any current. For 120V loads, however, the neutral is necessary to complete the circuit and carries the same amount of current as the hot conductor. Ground wires are never supposed to carry any current except when something goes wrong, but they are always required by code whether there is a neutral or not.

so why on a 120 voltcircuit you need a nuetral for a return path but its not needed for some 240 /480v applications bc your using two legs ?

 

[GoldDigger]

so why on a 120 voltcircuit you need a nuetral for a return path but its not need for some 240 480v applications bc you using two legs ?

1. There does not necessarily even have to be a neutral in a circuit. But if one of the loads has to connect to the neutral, the wire has to be there to carry current.
2. In your example, if I am interpreting it correctly, a 480 volt load does not need any connection to the wire which is one side of a 240 volt pair.
3. A single-phase load which connects from one phase wire to another on a delta does not require a neutral. But if you have a load which requires the same voltage as a wye load, then you have to provide a current carrying wire in the neutral position.
4. If you have a completely balanced three phase load, then whether it is wired internally as wye or delta, there is no need for the neutral point (not neutral wire) to even be there outside the load since all of the current will flow in the phase wires.
5. In a 240/120 split phase service, the only points between which the voltage is 120 are the neutral and each of the phase wires. So you have to use it for 120 volt loads.
6. For a 240 volt load in a 240/120 system, there is nothing to connect to the neutral in the first place.

 

[kwired]

so why on a 120 voltcircuit you need a nuetral for a return path but its not needed for some 240 /480v applications bc your using two legs ?

Basic electricity 101.

A 120 volt load needs 120 volts to operate as designed. Connect it to a common 120/240 single phase system - the only point on the system that has 120 volts to any other conductor is the neutral point, so this load must be connected between neutral and either L1 or L2.

On same system if you have a 240 volt load, the same thing applies. The only points on the system that have 240 volts between them are L1 and L2. Neutral is of no use to us for this load.

Take a household electric range or clothes dryer, that often has both 120 and 240 volt loads in the same appliance we run all three conductors so that all three are available to the loads within the appliance that need them.

 

[liquidtite]

Ok I understand but how does the current get back to the source with no return path when using straight 240/480

 

[Smart $]

Ok I understand but how does the current get back to the source with no return path when using straight 240/480

Not exactly sure what you mean by straight 240/480. Assuming you mean a split single phase system with 240V L1-N or L2-N and 480V L-L, it is not a common U.S. premises voltage system, but I have have seen it on occasion used for control voltage systems. It is no different than using a 120/240 other than voltage level. (Another instance is 480/240V 3? 4W delta system with grounded center tap, but I think that is a digression from the topic at hand...)

Apparently you don't understand return path. For a moment, consider a wire that is run in a circle... no beginning, no end. This is a circuit... but not a very useful one at that. Now let's cut this wire and insert a voltage source. Still a circuit and still not a very useful one... so we cut it again and insert a load (e.g. a lamp). Since we cut the wire twice, we now have two wires, and this proves we must have at least two wires for any useful circuit

No matter what these two wires are called, current leaves the source on one wire and returns on the other at any single instance. With alternating current, the direction change 120 times per second for 60Hz systems. We typically do not consider the brief instance when current is zero on change of direction in our discussions.

Now when you have a three-wire circuit, current leaves the source on one or two wires, and returns on two or one wire(s) respectively... if all three are conducting current. The instantaneous voltage coupled with the load configuration is what determines which wire(s) has current leaving the source and which wire(s) has current returning to the source. It may be that one is not conducting current... but it can never be that only one is conducting current and the other two are not, except during an abnormal condition, aka fault condition. What leaves must return... in some manner.

Now, coupled with what others have posted, please elaborate as best you can what it is you still do not understand.