Electricity wants to go to ground?

[realolman]

I don't understand why it is in any way more desirable to hook up loads phase to neutral than phase to phase. Why would you want to do that?

Re: the second neutral... seems to me that if it is a neutral, it has to carry current under normal conditions... otherwise it is not a neutral.

I also don't see the reasoning of a separate ground wire in a situation where any current it would ever carry would have to travel through the ground to get there... once it's in the ground the resistance of the earth is zero. It would cause another voltage drop at the ground rod that connects the second "neutral" to the earth. ... unlike the ECG, which is connected to materials that have good conductance .

So any fault current would have to connect to earth, travel through the earth to a ground rod, go back through the ground rod to a conductor that has more resistance than the earth from whence it just came?!? the whole deal doesn't make any sense to me

 

[mbrooke]

I don't understand why it is in any way more desirable to hook up loads phase to neutral than phase to phase. Why would you want to do that?

Re: the second neutral... seems to me that if it is a neutral, it has to carry current under normal conditions... otherwise it is not a neutral.

I also don't see the reasoning of a separate ground wire in a situation where any current it would ever carry would have to travel through the ground to get there... once it's in the ground the resistance of the earth is zero. It would cause another voltage drop at the ground rod that connects the second "neutral" to the earth. ... unlike the ECG, which is connected to materials that have good conductance .

So any fault current would have to connect to earth, travel through the earth to a ground rod, go back through the ground rod to a conductor that has more resistance than the earth from whence it just came?!? the whole deal doesn't make any sense to me

Some Utilitys may choose to run an EGC some not. Running an EGC increases the chances of an earth fault being detected, keep in mind the earths resistance varies widely. Wet soil will have a much lower resistance then lets say frozen earth during winter or dry sandy soil in an arid climate. When earth alone is used as a conductor you loose the redundancy of multiple grounds and bargin with the soil resistance wich can be near zero ohms to in the thousands.

Hooking loads phase to neutral can be more cost effective because of the 3sqrt voltage reduction. There are manly other variables that govern this too. All methods are give and take in money, safety, risk, transient stability, service continuity ect ect. Its the job for an engineer to see which is most suited for the job.

 

[mbrooke]

I have to agree with this statement! Also some here fail to understand that utilities are regulated by the NESC. This standard says where and how a system is to be grounded. The standard is property of IEEE. Have the rules changed in the governing standard if it is such an issue. There are just as many causes of stray voltage caused by customer equipment issues. A faulty neutral connection in a meter base will cause problems with stray voltage, just as bad as a faulty MGS.

All MGNs will produce stray current faulty or not, its simple fact of wire naturally being a non perfect conductor. The larger the neutral the less current is placed on earth. In an average MGN system about half the current divides between the earth and neutral. And yes, customer wiring to can be a cause in stray current as well, have seen it first hand in well pumps and broken underground cables to garages and sheds. But keep in mind not every customer has faults causing current through earth while nearly every pole has a grounded current carrying neutral. I am well aware the the NESC governs most utility installations, but keep in mind that code is a bare minimum. The NEC and the NESC are to completely different animals. Having worked with both, in my opinion the NEC is superior to the NESC.

 

[mivey]

Also some here fail to understand that utilities are regulated by the NESC.

Utilities are regulated by the state. Many states (not sure how many) choose to let the non-investor owned utilities "regulate" themselves. The idea is that with an IOU, the customer has no representative other that the regulating authority. That regulating authority (usually the public service commission) can make the IOUs comply with the NESC but may have no jurisdiction to force the non-IOUs to comply.

In a non-IOU, the customer has a vote during the electing of boards, etc. so they have a voice and, for the most part, do not need a regulating authority to protect their interests. In other words, the non-IOUs are "self-ruled" by the members / voting customers.

The NESC regulates nothing. It is a voluntary code. Many utilities have their own safety guidelines that may differ from the NESC. A state can adopt the NESC and force the utility to comply with it, but I don't know how many do.

That said, a utility that opts to develop their own safety code also takes the responsibility of defending that code in court. It is much easier, and probably much wiser, to use what has become an industry standard. In that respect, the NESC is usually the "go-to" source for what a utility should do as a minimum. But it is not always true that a utility must comply with the NESC.

 

[realolman]

Some Utilitys may choose to run an EGC some not. Running an EGC increases the chances of an earth fault being detected, keep in mind the earths resistance varies widely. Wet soil will have a much lower resistance then lets say frozen earth during winter or dry sandy soil in an arid climate. When earth alone is used as a conductor you loose the redundancy of multiple grounds and bargin with the soil resistance wich can be near zero ohms to in the thousands.

Is it the earth's resistance to which you are referring, or the resistance of the ground rod to earth connection, which is what I'm talking about.

Hooking loads phase to neutral can be more cost effective because of the 3sqrt voltage reduction. .

What does that mean ?... please explain.:?

 

[mbrooke]

Is it the earth's resistance to which you are referring, or the resistance of the ground rod to earth connection, which is what I'm talking about.



What does that mean ?... please explain.:?

I am mainly referring to the resistance between 2 ground rods. Continuity between 2 or more rods varys on depth driven and soil conditions. Take 2 ground rods, drive them 10 feet apart of each other and measure the resistance in ohms between the 2. Now do the same in mud after a rain storm. The resistance in the mud will be much lower.

Phase to neutral voltage is always lower than phase to phase. To find the neutral voltage potential between a phase divide by the square root of 3. On a 4160 volt system the phase to neutral voltage is 2400. 12470 volt divided by 3 sqrt= 7200volt. Some times it is cheaper to use a transformer insulated at a lower voltage.

 

[realolman]

I am mainly referring to the resistance between 2 ground rods. Continuity between 2 or more rods varys on depth driven and soil conditions. Take 2 ground rods, drive them 10 feet apart of each other and measure the resistance in ohms between the 2. Now do the same in mud after a rain storm. The resistance in the mud will be much lower.

That is exactly why I am saying that it doesn't make much sense to run another ground wire along with the other conductors when it has to depend on a (not very good) connection between the ground rod and the earth, and the connection between the fault and the earth , and the resistance of the conductor itself, when the earth itself has so many paths for current flow that it has a resistance of zero

Phase to neutral voltage is always lower than phase to phase. To find the neutral voltage potential between a phase divide by the square root of 3. On a 4160 volt system the phase to neutral voltage is 2400. 12470 volt divided by 3 sqrt= 7200volt. Some times it is cheaper to use a transformer insulated at a lower voltage.

I don't really know how to figure it, but it seems to me the cost of the windings, conductors, and voltage drop would offset any savings from using 7200 v insulators compared to 13000 v insulators ( or 2400 to 4160 )

 

[kwired]

That is exactly why I am saying that it doesn't make much sense to run another ground wire along with the other conductors when it has to depend on a (not very good) connection between the ground rod and the earth, and the connection between the fault and the earth , and the resistance of the conductor itself, when the earth itself has so many paths for current flow that it has a resistance of zero




I don't really know how to figure it, but it seems to me the cost of the windings, conductors, and voltage drop would offset any savings from using 7200 v insulators compared to 13000 v insulators ( or 2400 to 4160 )

Exactly. It is no different than deciding whether to use 277/480 or 120/208. The amount of load, and length of circuits kind of dictates which way is better way to do to some degree.

Most distribution systems in small towns here is 4160/2400. Most of them are loaded enough the guys that maintain them wish they had 12500/7200. I have worked at many small plants that have 120/208 or 120/240, and it sure would be nice to have 277/480 instead, when it comes to conductor and equipment costs.

 

[Hv&Lv]

Utilities are regulated by the state. Many states (not sure how many) choose to let the non-investor owned utilities "regulate" themselves. The idea is that with an IOU, the customer has no representative other that the regulating authority. That regulating authority (usually the public service commission) can make the IOUs comply with the NESC but may have no jurisdiction to force the non-IOUs to comply.

In a non-IOU, the customer has a vote during the electing of boards, etc. so they have a voice and, for the most part, do not need a regulating authority to protect their interests. In other words, the non-IOUs are "self-ruled" by the members / voting customers.

I do not agree with this statement. RUS, which is a part of the USDA, regulates the coopratives. http://www.rurdev.usda.gov/Utilities_LP.html I do not know of a state that has their own code. http://grouper.ieee.org/groups/nesc/PUCsurvey2007.pdf title 7, 1725.50 http://ecfr.gpoaccess.gov/cgi/t/tex...1.1.2.1.10;idno=7;cc=ecfr#7:11.1.2.1.10.5.2.1

The NESC regulates nothing. It is a voluntary code. Many utilities have their own safety guidelines that may differ from the NESC. A state can adopt the NESC and force the utility to comply with it, but I don't know how many do.

You are correct. I used the wrong word. The NESC is just like the NEC. It has to be adopted to become law. I do not agree that many utilities have their own safety guidlines. http://grouper.ieee.org/groups/nesc/PUCsurvey2007.pdf

 

[mivey]

I do not agree with this statement.

Then you do not know what you are talking about.

RUS, which is a part of the USDA, regulates the coopratives.

No, they do not.

I do not know of a state that has their own code.

California is notorious for doing things their own way. It would not suprise me one bit if they have deviated from the NESC in one way or another. Think about how many states deviate from the NEC as written.

I do not agree that many utilities have their own safety guidlines.

Then you have not worked with many utilites. What do you think they did before the NESC came along? Who do you think helped develop some of the NESC guidelines? Do you think every utility agrees with everything the NESC does and would waive the safety practices they have been developing for well over 100 years?

 

[kwired]

If NESC is adopted as law, who is enforcing it, besides utilities policing themselves? For the most part only if there is an accident would anything be questioned. That said it is not law - at least most places but it is an industry standard and would still likely be looked at in a legal situation if they are trying to determine who is at fault after an accident.

 

[mivey]

If NESC is adopted as law, who is enforcing it, besides utilities policing themselves? For the most part only if there is an accident would anything be questioned.

That is very sad but true. More often than not, the state agencies tasked with oversite are under-funded and under-staffed and there are a lot of things that fall throught the cracks. But when it goes bad, the government-regulated utilites know the sleeping giant will wake up and make their lives miserable. This is a check in itself and most utilities make a valid effort to comply with the standards.

That said it is not law - at least most places but it is an industry standard and would still likely be looked at in a legal situation if they are trying to determine who is at fault after an accident.

That, I believe, is why most utilites are wise to at least meet the minimum set forth in the NESC as it would be hard for an attorney to argue against it. But they will beat you over the head with it and try to make the jury think it says things that it really does not say.

 

[Hv&Lv]

Then you do not know what you are talking about.

No, they do not.

California is notorious for doing things their own way. It would not suprise me one bit if they have deviated from the NESC in one way or another. Think about how many states deviate from the NEC as written.

Then you have not worked with many utilites. What do you think they did before the NESC came along? Who do you think helped develop some of the NESC guidelines? Do you think every utility agrees with everything the NESC does and would waive the safety practices they have been developing for well over 100 years?

I am sorry you feel the need for a condescending attitude within your posts. I am done.

 

[mivey]

I am sorry you feel the need for a condescending attitude within your posts. I am done.

Sorry if I was too blunt. I don't always have the time or patience to make long posts and fill them with supporting data. I guess I should not have just blurted it out like that but I don't claim to always do everything right.

Perhaps you will take the opportunity to do a little research on your own. I dropped a few thoughts as to where and what you might look into if you wanted to find out for yourself and do a little historical research. I'll be glad to get you more information if you can't find any.

My apologies if you were offended.