NEUTRAL CONDUCTOR FROM THE DISTRIBUTION UTILITY

[iwire]

There is a difference between less conductivity and insufficient conductivity.

The use of a steel messenger provides sufficient conductivity to operate the breaker.

Are you aware steel conduit is used every day as the only fault path?

 

[bobby ocampo]

There is a difference between less conductivity and insufficient conductivity.

The use of a steel messenger provides sufficient conductivity to operate the breaker.

Are you aware steel conduit is used every day as the only fault path?

What is the condition for this less conductivity? How less is acceptable? What is the condition required to determine if the single phase system is effectively grounded in 3phase system IEEE 142 have this conditions.

1.2.1 effectively grounded:Grounded through a sufficiently low impedance such that for all system conditions the ratio of zero-sequence reactance to positive-sequence reactance (X0/X1) is positive and not greater than 3, and the ratio of zero-sequence resistance to positive-sequence reactance (R0/X1) is positive and not greater than 1.

Simple grounding of the neutral in 3phase is not a guarantee that the system is effectively grounded. Any definition of effectively grounded in the single phase, 3wire?

Having a resistance in the neutral in a case of line to ground and the length of this messenger wire from the transformer may be high enough not to operate the OCPD?

 

[don_resqcapt19]

There is only a small increase in the resistance of the bare neutral conductor wire as compared to the insulated conductors of the cable. Most of the bare conductor is still aluminum, just like the insulated conductors. In many cases only a single strand of the bare conductor is replaced with steel.

 

[bobby ocampo]

There is only a small increase in the resistance of the bare neutral conductor wire as compared to the insulated conductors of the cable. Most of the bare conductor is still aluminum, just like the insulated conductors. In many cases only a single strand of the bare conductor is replaced with steel.

Is there a regulation on what type of messenger wire may be used for the neutral or grounded service conductor? What is the minimum size? Can the utility just use any material for the messenger wire? Is there a rule that it should be either aluminum or copper only? Can they use steel?

 

[jim dungar]

Is there a regulation on what type of messenger wire may be used for the neutral or grounded service conductor? What is the minimum size? Can the utility just use any material for the messenger wire? Is there a rule that it should be either aluminum or copper only? Can they use steel?

Have you tried searching for information on messenger conductors or ACSR, which is typically used in the installation you are questioning?
Southwire, Inc has conductor properties available on their website.

 

[electricianexpress]

I always thought that the neutral was sizes smaller the same as seu cable is. The messenger cable, although integrated with the neutral, is not calculated with the neutral.

 

[don_resqcapt19]

Is there a regulation on what type of messenger wire may be used for the neutral or grounded service conductor? What is the minimum size? Can the utility just use any material for the messenger wire? Is there a rule that it should be either aluminum or copper only? Can they use steel?

You will have to look elsewhere for that type of information. This is an NEC forum and the NEC does not apply to those conductors.

 

[mbrooke]

There is a difference between less conductivity and insufficient conductivity.

The use of a steel messenger provides sufficient conductivity to operate the breaker.

Are you aware steel conduit is used every day as the only fault path?

Apples to oranges. The purpose of a neutral is not only to provide a low current fault path.

 

[kwired]

Apples to oranges. The purpose of a neutral is not only to provide a low current fault path.

His point was that the steel is still low enough resistance to allow sufficient fault current to flow to facilitate operation of an overcurrent device. A little lower conductivity level will cause longer time necessary for operation of the device - but then same can happen with a longer run of copper as the resistance of that conductor does increase as the circuit gets longer as well.

If such details of knowing exactly what the fault current level will be are important then one needs to calculate based on properties of the conductor involved be it copper, aluminum, steel, combination of aluminum and steel, or any other conductive material for that matter. One material may be better in some circumstances then others, yet a larger size of another material may cost less and give similar performance. Putting one steel strand in an aluminum conductor to give it some support strength for aerial application is usually not a big deal - and with multiconductor assembly like we are talking about this particular conductor is also typically the neutral conductor and is only carrying unbalanced current of the ungrounded conductors so likely could be a smaller conductor if it were all aluminum in most cases anyhow.

 

[iwire]

Apples to oranges. The purpose of a neutral is not only to provide a low current fault path.

It is not apples to oranges when responding to post about overcurrent operation. Try to follow along.


But the fact remains even as a current carrying circuit conductor a properly sized messenger cable is sufficient for the job.

 

[kwired]

It is not apples to oranges when responding to post about overcurrent operation. Try to follow along.


But the fact remains even as a current carrying circuit conductor a properly sized messenger cable is sufficient for the job.

The steel strand is in the center of the conductor - doesn't the majority of current flow near the outer surface of the conductor - and if so is the "conductivity" of said conductor really much different then if it were all aluminum? I can imagine it is different, but probably not significantly different, and when you look at how much current we typically limit a specific conductor to just to prevent it from failing compared to what it actually can carry, we are usually not even close to loading most conductors to their potential ability. Then throw in the fact this conductor is free air with no insulation and we can operate it at an even higher temperature before something fails.

 

[iwire]

- doesn't the majority of current flow near the outer surface of the conductor .

My very limited understating of the skin effect is that with 60Hz circuits it is not a factor until we get into very large conductors, such as 750 kcmil and above.


I am a pretty simply guy and my view is that hundreds of thousands of installations over decades of time have proven it works.

Much like how the utility can successfully use much smaller ungrounded conductors than the NEC would allow.

 

[kwired]

My very limited understating of the skin effect is that with 60Hz circuits it is not a factor until we get into very large conductors, such as 750 kcmil and above.


I am a pretty simply guy and my view is that hundreds of thousands of installations over decades of time have proven it works.

Much like how the utility can successfully use much smaller ungrounded conductors than the NEC would allow.

I agree that there has been much successful applications over several years - something must work there.

I also have limited understanding of skin effect but think that 750 kcmil level is maybe a little high, and may be part of reason why we do parallel conductors that are smaller then that. I get the feeling those factors maybe become significant enough to kick in at maybe even 300 or 400 kcmil - especially with aluminum conductors. But may still be significant enough that a steel strand in a 2AWG aluminum likley doesn't change it's current carrying ability all that much over all aluminum strands, it may cause more heat at the surface but there is no insulation on this conductor to worry about either which is what the heat issue is about with conductors in general.

 

[iwire]

I also have limited understanding of skin effect but think that 750 kcmil level is maybe a little high,

It might be.

This from wikipedia so take it with a grain of salt

The skin effect is due to opposing eddy currents induced by the changing magnetic field resulting from the alternating current. At 60 Hz in copper, the skin depth is about 8.5 mm.

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

That would mean it has zero effect until we get above a 300Kcmil

and may be part of reason why we do parallel conductors that are smaller then that. I get the feeling those factors maybe become significant enough to kick in at maybe even 300 or 400 kcmil - especially with aluminum conductors. But may still be significant enough that a steel strand in a 2AWG aluminum likley doesn't change it's current carrying ability all that much over all aluminum strands, it may cause more heat at the surface but there is no insulation on this conductor to worry about either which is what the heat issue is about with conductors in general.

I think the bigger reason that we get less amps per unit of copper with larger conductors has to do with heat dispensation problems.

 

[kwired]

It might be.

This from wikipedia so take it with a grain of salt


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

That would mean it has zero effect until we get above a 300Kcmil









I think the bigger reason that we get less amps per unit of copper with larger conductors has to do with heat dispensation problems.

Possibly has been experimented with before but one could make a superconductor so to speak by making the conductive portion a tube and run a coolant through the center

 

[bobby ocampo]

Based on the orientation of the meter. We can see that neutral conductor is not only for the operation of the fault current. The meter can read the losses in the neutral cable. Does it mean that it is to the distribution utility's advantage to install neutral that has less conductivity so that the meter reading will be higher as compared with a good conductor neutral?

 

[bobby ocampo]

Definition of Messenger Wire

"A messenger wire is a wire or cable that is used solely for the physical support of another element, typically a conductive wire or bundle of wires. The messenger wire will take the shape of a parabola (shape of a free hanging string) and the conductive wore or bundle of wires supported by the messenger may follow that parabola of be supported in a straight lines through the use of drop lines."

If the messenger wire used by the utility is just an any type of wire or cable, this will surely have high resistance and high resistance means more line losses that the meter will surely measure. The longer this messenger wires are from the transformer to the service drop, the higher will be the line losses.

Not to mention the possibility that if effectively grounding is not met, OCPD may not operate.

Should there be a regulation on the type of messenger wire that should be used? Maybe not by NEC but other regulation where distribution utility should comply.

 

[bobby ocampo]

What body regulates Distribution Utility in the USA?

 

[don_resqcapt19]

Definition of Messenger Wire

"A messenger wire is a wire or cable that is used solely for the physical support of another element, typically a conductive wire or bundle of wires. The messenger wire will take the shape of a parabola (shape of a free hanging string) and the conductive wore or bundle of wires supported by the messenger may follow that parabola of be supported in a straight lines through the use of drop lines."
....

That does not describe triplex or quadplex type cables. The bare conductor in those types of cables is both the messenger and a circuit conductor.

 

[GoldDigger]

Definition of Messenger Wire

"A messenger wire is a wire or cable that is used solely for the physical support of another element, typically a conductive wire or bundle of wires. The messenger wire will take the shape of a parabola (shape of a free hanging string) and the conductive wore or bundle of wires supported by the messenger may follow that parabola of be supported in a straight lines through the use of drop lines."

If the messenger wire used by the utility is just an any type of wire or cable, this will surely have high resistance and high resistance means more line losses that the meter will surely measure. The longer this messenger wires are from the transformer to the service drop, the higher will be the line losses.

Not to mention the possibility that if effectively grounding is not met, OCPD may not operate.

Should there be a regulation on the type of messenger wire that should be used? Maybe not by NEC but other regulation where distribution utility should comply.

I appreciate that the definition gets the math close to right. A string, wire or cable supporting only its own weight describes a *catenary* curve. But the cables of s suspension bridge, where the weight of the deck is far greater than the weight of the cable itself is in fact a parabola. The definition assumes that the weight of the conducting wires is much greater than the weight of the messenger wire alone and that they are not simply bundled together.