NEUTRAL CONDUCTOR FROM THE DISTRIBUTION UTILITY

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bobby ocampo

Senior Member
Any standard that a Distribution Utility should comply in this grounded service conductor or neutral? Should it have a minimum size or specification?

Should the end user allow the Distribution Utility to charge him with the line losses of the grounded service conductor or neutral conductor?
 

kwired

Electron manager
Location
NE Nebraska
Any standard that a Distribution Utility should comply in this grounded service conductor or neutral? Should it have a minimum size or specification?

Should the end user allow the Distribution Utility to charge him with the line losses of the grounded service conductor or neutral conductor?
Line losses happen in all conductors unless you can find one that has absolutely no resistance.

There are also losses in transformers and other distribution components - ultimately the consumers are paying for those losses, but not through direct metering of those losses. Why do you think the customer meter records line losses ahead of the meter? True the neutral conductor most cases isn't even metered, but what comes in on the ungrounded conductors is, and if it doesn't come back on the other ungrounded conductor(s) it doesn't get added to the count.

There are single phase 120/240 metering systems that use a single CT to capture current for the metering. Both ungrounded conductors pass through this CT but in opposite directions in relation to the supply side. There may be a little more to this but to keep things simple it is basically metering at 120 volts, should there be a 240 volt load the current in the CT is doubled because both circuit conductors are passing through the CT - it doesn't matter that the neutral isn't monitored, because all the current of a 120 volt circuit is equal in all portions of the circuit, so if the ungrounded conductor passes through the meter you have already captured the current of that load for metering, and it could care less if the return path is the neutral conductor, the water pipe that was used as a grounding electrode, the shield on the phone cable or any other path.

Most states have regulations on delivered power as well, and the POCO's need to be within at least 10% of the nominal voltage, probably at the metering point, or possibly wherever customer owned equipment starts anyway. Also keep in mind the neutral is generally only carrying imbalanced current of the other conductors, so better balancing will ensure less neutral losses. For a typical residential service I'd guess the losses in the neutral would be low enough it doesn't matter much, for a higher demand commercial or industrial facility, they are probably looking closer at their own losses beyond the service point and trying to maintain balance anyway.

I won't say there is no losses in the unmonitored neutral conductor because obviously if there is a voltage drop across any conductor there is a resistive loss. But what is voltage drop going to be over a reasonably balanced neutral to a typical residential or light commercial service? Remember if you are measuring line to neutral voltage at the service any drop you see there is a composition of drop in both grounded and ungrounded conductors, you need to measure the drop across the neutral itself to see what is lost in the neutral. If you only have a 1.5 volt drop and a current of 10 amps that is a 15 watt loss. If your energy rate is 10 cents/kWhr that is .15 cents per hour lost - assuming that you maintain that load creating this loss for an hour. If you kept that load constant for 24 hours you lost 3.6 cents in one day. Dwelling and light commercial loads are usually not that constant so chances are you have high and low periods throughout any given day - but the net is possibly lower then this example. One could possibly offset that cost easily just by remembering to turn off a light in a space that doesn't get much use.

Larger services usually have large conductors and they are usually underground - so no steel strand in those cases, yet they often have neutral issues involving harmonics and can still have losses on the unmetered neutral conductor.

POCO medium and high voltage distribution/transmission overhead lines also use conductors with a steel strand for added support - if they didn't those lines would come down much more often then they do, or we would need much closer spacing between support poles/towers. Either way those things probably end up costing much more then what little loss there may be because of reduced conductivity that results in that steel strand.

I went to an open house Q&A session a couple years ago, related to a current transmission line project that is now starting in the area. This was for a 345kV line being built in the area. Though it was the "shield" wire that they had a sample of - they can embed fiber optic strands into those overhead lines as well for communications between substations, switch yards, etc.

It all comes down to knowing what you have for a conductor and setting a design standard when it comes to determining what size of conductor is needed. POCO's do often have their own standards, but also need to comply with utility regulating commissions, when it comes to quality of what gets delivered to the consumer, and they usually can meet those standards with less restriction in materials selection then if they would have to follow the NEC for selecting conductor sizes. I can't tell you how many times I have seen residential service drop of only #2 or #4 AWG aluminum (with steel strand in the neutral) supplying a 200 amp service - but seldom see any troubles with that service either - because the service is not really loaded that much or for very long if it does have a fairly significant load at times. If you want them to change things like this - it will cost the consumer more money then what losses are on current designs in most instances.
 

GoldDigger

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kwired,
Please reread my post, #18, for an explanation of why standard metering is affected by VD (losses) in the neutral but not in the ungrounded conductors.
The problem is not in the current measurement but rather in the voltage measurement.
 

don_resqcapt19

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Location
Illinois
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retired electrician
...

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

...
If the fault is on the line side of the service OCPD, it is rare that any OCPD will open the circuit. Typically the conductors act as fuses for line side faults.
Also, grounding really has nothing to do with the operation of the OCPD.
 

kwired

Electron manager
Location
NE Nebraska
kwired,
Please reread my post, #18, for an explanation of why standard metering is affected by VD (losses) in the neutral but not in the ungrounded conductors.
The problem is not in the current measurement but rather in the voltage measurement.

I kind of rambled on a little with information I didn't have exact details for. I guess I don't get why bobby o seems to think there is as big of a problem as he wants to think there is with the current carrying abilities of a conductor with a steel strand inserted into it for support reasons - and on top of that for a conductor typically that doesn't need to be physically as large as it's associated ungrounded conductors. I believe he brought up the metering issue as something to blame any loss as well as any resulting metering error on the POCO, though any loss in any neutral conductor (in particular on the POCO side) will have similar results when it comes to recording energy usage - so it still turns out to be either we need to redesign metering - which may cost us more then living with any errors we now have, or those that design need to consider that those particular conductors have a different resistance then conductors without the steel strand when making design desisions - which I'd bet they often do take that into consideration, but the neutral also typically doesn't need to be as large as the ungrounded conductors either.
 

bobby ocampo

Senior Member
I kind of rambled on a little with information I didn't have exact details for. I guess I don't get why bobby o seems to think there is as big of a problem as he wants to think there is with the current carrying abilities of a conductor with a steel strand inserted into it for support reasons - and on top of that for a conductor typically that doesn't need to be physically as large as it's associated ungrounded conductors. I believe he brought up the metering issue as something to blame any loss as well as any resulting metering error on the POCO, though any loss in any neutral conductor (in particular on the POCO side) will have similar results when it comes to recording energy usage - so it still turns out to be either we need to redesign metering - which may cost us more then living with any errors we now have, or those that design need to consider that those particular conductors have a different resistance then conductors without the steel strand when making design desisions - which I'd bet they often do take that into consideration, but the neutral also typically doesn't need to be as large as the ungrounded conductors either.

Based on the illustration. What MATERIAL should the distribution utility used for the grounded service conductor? What size is the minimum? Can the utility use regular GI wire as the messenger wire for the neutral or the grounded service conductor?

Any Energy Regulatory Code or Distribution Code that the DU will have to comply to make sure that the messenger wire complies with the minimum size of grounded service conductor?
 

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bobby ocampo

Senior Member
Line losses happen in all conductors unless you can find one that has absolutely no resistance.

The issue is in what conductor the Distribution Utility will use. It is obvious that all conductors have resistance. However, if the DU will use a conductor that has small cross sectional we all know that it has a higher resistance than a big cross sectional area. If the Distribution utility will use a lower cross sectional area then there will be losses.

There are also losses in transformers and other distribution components - ultimately the consumers are paying for those losses, but not through direct metering of those losses. Why do you think the customer meter records line losses ahead of the meter? True the neutral conductor most cases isn't even metered, but what comes in on the ungrounded conductors is, and if it doesn't come back on the other ungrounded conductor(s) it doesn't get added to the count.

Again the issue is the the GROUNDED SERVICE CONDUCTOR or the neutral conductor that the distribution will use. The lower the cross sectional are the more resistance and therefore more losses. Less conductivity material for the same cross sectional area has more losses. There should be a minimum size of neutral service conductor that should be used. Any Distribution Utility Standard from the US government?

There are single phase 120/240 metering systems that use a single CT to capture current for the metering. Both ungrounded conductors pass through this CT but in opposite directions in relation to the supply side. There may be a little more to this but to keep things simple it is basically metering at 120 volts, should there be a 240 volt load the current in the CT is doubled because both circuit conductors are passing through the CT - it doesn't matter that the neutral isn't monitored, because all the current of a 120 volt circuit is equal in all portions of the circuit, so if the ungrounded conductor passes through the meter you have already captured the current of that load for metering, and it could care less if the return path is the neutral conductor, the water pipe that was used as a grounding electrode, the shield on the phone cable or any other path.

I have attached in my previous comment the schematic diagram of the single phase, 3wire metering system. It is clear that the meter will measure the kwhr consumption of 120 volts load and therefore will also measure the line losses of the GROUNDED SERVICE CONDUCTOR. We all know the factors that affect the resistance, cross sectional area, length of the neutral conductor, material used as a grounded service conductor.

Most states have regulations on delivered power as well, and the POCO's need to be within at least 10% of the nominal voltage, probably at the metering point, or possibly wherever customer owned equipment starts anyway. Also keep in mind the neutral is generally only carrying imbalanced current of the other conductors, so better balancing will ensure less neutral losses. For a typical residential service I'd guess the losses in the neutral would be low enough it doesn't matter much, for a higher demand commercial or industrial facility, they are probably looking closer at their own losses beyond the service point and trying to maintain balance anyway.

Neutral is current carrying. If there is a line to neutral load or 110 volts, are we saying that the neutral is zero current?

I won't say there is no losses in the unmonitored neutral conductor because obviously if there is a voltage drop across any conductor there is a resistive loss. But what is voltage drop going to be over a reasonably balanced neutral to a typical residential or light commercial service? Remember if you are measuring line to neutral voltage at the service any drop you see there is a composition of drop in both grounded and ungrounded conductors, you need to measure the drop across the neutral itself to see what is lost in the neutral. If you only have a 1.5 volt drop and a current of 10 amps that is a 15 watt loss. If your energy rate is 10 cents/kWhr that is .15 cents per hour lost - assuming that you maintain that load creating this loss for an hour. If you kept that load constant for 24 hours you lost 3.6 cents in one day. Dwelling and light commercial loads are usually not that constant so chances are you have high and low periods throughout any given day - but the net is possibly lower then this example. One could possibly offset that cost easily just by remembering to turn off a light in a space that doesn't get much use.

For the sake of discussion, what if the DU used a GI wire as the messenger wire? Will it have the same losses?

Larger services usually have large conductors and they are usually underground - so no steel strand in those cases, yet they often have neutral issues involving harmonics and can still have losses on the unmetered neutral conductor.

Again if the neutral service conductor provided by the utility is too small what will happen to the losses?

POCO medium and high voltage distribution/transmission overhead lines also use conductors with a steel strand for added support - if they didn't those lines would come down much more often then they do, or we would need much closer spacing between support poles/towers. Either way those things probably end up costing much more then what little loss there may be because of reduced conductivity that results in that steel strand.

The issue is not with the ACSR if used as the messenger wire. Is there a standard that says that it should be ACSR as the messenger wire? What size? What is the calculation to know if the messenger wire is properly sized by the DU?

I went to an open house Q&A session a couple years ago, related to a current transmission line project that is now starting in the area. This was for a 345kV line being built in the area. Though it was the "shield" wire that they had a sample of - they can embed fiber optic strands into those overhead lines as well for communications between substations, switch yards, etc.

Again the issue is on a single phase, 3wire system

It all comes down to knowing what you have for a conductor and setting a design standard when it comes to determining what size of conductor is needed. POCO's do often have their own standards, but also need to comply with utility regulating commissions, when it comes to quality of what gets delivered to the consumer, and they usually can meet those standards with less restriction in materials selection then if they would have to follow the NEC for selecting conductor sizes. I can't tell you how many times I have seen residential service drop of only #2 or #4 AWG aluminum (with steel strand in the neutral) supplying a 200 amp service - but seldom see any troubles with that service either - because the service is not really loaded that much or for very long if it does have a fairly significant load at times. If you want them to change things like this - it will cost the consumer more money then what losses are on current designs in most instances.

What is the Distribution Regulating commission? Do they have a minimum standard for the DU?
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
...
Again the issue is the the GROUNDED SERVICE CONDUCTOR or the neutral conductor that the distribution will use. The lower the cross sectional are the more resistance and therefore more losses. Less conductivity material for the same cross sectional area has more losses. There should be a minimum size of neutral service conductor that should be used. Any Distribution Utility Standard from the US government? ...
The state utility commissions all have standards that set the minimum voltage that the utility can supply to the building. If the neutral conductor is too small, they can't supply the required voltage.
 

don_resqcapt19

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Location
Illinois
Occupation
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Any reference standard or Code?
As far as I know each state sets their only voltage standards. The utility has to size their system to provide voltage within the required range.

I am not really sure what is driving your questions.

All of the triplex and quadplex type service drop conductors I have seen, have a messenger that is the same physical size as the insulated conductors and will have almost the same current carrying capacity as the insulated conductors. The only difference is that the bare messenger will have one strand of aluminum replaced with a steel strand. Even if the steel was non-conductive, the messenger would have an ampacity of 85% of the insulated conductors. It would be a very rare installation where the neutral current was running anywhere near 85% of the phase currents.
 

kwired

Electron manager
Location
NE Nebraska
As far as I know each state sets their only voltage standards. The utility has to size their system to provide voltage within the required range.

I am not really sure what is driving your questions.

All of the triplex and quadplex type service drop conductors I have seen, have a messenger that is the same physical size as the insulated conductors and will have almost the same current carrying capacity as the insulated conductors. The only difference is that the bare messenger will have one strand of aluminum replaced with a steel strand. Even if the steel was non-conductive, the messenger would have an ampacity of 85% of the insulated conductors. It would be a very rare installation where the neutral current was running anywhere near 85% of the phase currents.
And if you have underground conductors, most of the time the neutral conductor will be a standard size or two smaller then the ungrounded conductors anyway so you still get somewhat similar performance without the ACSR in those applications.

ADD since this thread is supposed to be primarily addressing single phase dwelling/light commercial applications - typical 200 amp underground supply around here will be 4/0 aluminum ungrounded and 2/0 aluminum grounded conductors. Other common multiplexed underground conductor assemblies are (all aluminum conductors) 2-2/0 with 1-1AWG, 2-1/0 with 1-2AWG, 2 - 2AWG with 1-4 AWG, smaller then 4 AWG is usually all same sized, larger then 4/0 usually has neutral two sizes smaller - this for standard stocked URD assemblies.

With higher demand in the region for cables used to supply irrigation needs you can sometimes find some commonly used assemblies with smaller grounded conductor because for most of those applications the grounded conductor is not used for line to neutral loads and only needs to be sized for minimum grounding electrode conductor required for service applications or for minimum equipment grounding conductor needed for non service applications. But that is one of those things that is somewhat local based on demand of what people are asking for.
 
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bobby ocampo

Senior Member
As far as I know each state sets their only voltage standards. The utility has to size their system to provide voltage within the required range.

I am not really sure what is driving your questions.

All of the triplex and quadplex type service drop conductors I have seen, have a messenger that is the same physical size as the insulated conductors and will have almost the same current carrying capacity as the insulated conductors. The only difference is that the bare messenger will have one strand of aluminum replaced with a steel strand. Even if the steel was non-conductive, the messenger would have an ampacity of 85% of the insulated conductors. It would be a very rare installation where the neutral current was running anywhere near 85% of the phase currents.

Any reference that will refer to this 85%? What government agency in the US regulates the Distribution Utility?
 

kwired

Electron manager
Location
NE Nebraska
Why can't you understand if the regulation state voltage needs to be within say 10 percent, that there may be multiple causes for voltage fluctuations as well as multiple ways of dealing with voltage that is out of range?

On customer service conductors of less then 1000 volts most methods are simply larger conductors to compensate for voltage drop. That sizing is not so much directly regulated as the load end measured voltage is - leaving how to fix a problem up to the power supplier. You can have have a standard of supplying 200 amp services with a certain size cable and have little problems in general, but there is that occasional service that has a longer conductor run or a little higher load then usual that needs extra attention - and usually never gets it unless the consumer complains about troubles after the problem is there. They can also supply you conductors that do handle the load just fine, but if they have an undersized transformer you still may not see sufficient voltage. Then there is occasionally trouble with the primary distribution side leaving you with low or even too high of voltage, but that is usually temporary and a result of a component failure.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Any reference that will refer to this 85%? What government agency in the US regulates the Distribution Utility?
The 85% is based on a 7 conductor cable with 6 stands of aluminum and one strand of steel...for the purposes of the calculation I assumed the use of non-conductive steel:).

I am not sure any US agency regulates distribution...unless it crosses state lines it would be a state issue.

Why don't you tell us what you see as the real world problem here?

There is no reason for the utility to have to do something that the NEC does not require for the premisses wiring. The NEC requires that the grounded (neutral) have an ampacity that is equal to the calculated load on the neutral or be sized based on the size of the service entrance phase conductors. You rare required to use the larger of the two. See 250.24(C)(1) and 220.61. In most cased the neutral is sized by Table 250.102(C)(1). 250.24(C)(1) sends you to that table.

The table permits the grounded conductor to be much smaller than the reduced sizes we are talking about with the typical service cables used by the utility.
 

bobby ocampo

Senior Member
Form 2s meter is used for 230 volts single phase, 3 wire. Using this meter, can it measure consumption of line to neutral loads?
 

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bobby ocampo

Senior Member
Will this Form 2s meter measure line to neutral loads?
 

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mivey

Senior Member
Will this Form 2s meter measure line to neutral loads?
Yes, but with a slight degree of inaccuracy. The current is measured accurately but the voltage is measured line-line instead of line-neutral. This means it is assumed that the line-neutral voltages are relatively balanced, which is a reasonable assumption in most cases.
 
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