earley power co
- Thread starter domnic
- Start date
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Are tyou asking if they just drove a ground rod for the grounded conductor? If so it would never work.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Nonetheless, it has been done. It's called SWER, which stands for Single Wire, Earth Return.
You'd only see it for primary distribution, and only for single phases, and mostly rural areas.
It seems that, the higher the voltage, the better the earth is at being an effective conductor.
You'd only see it for primary distribution, and only for single phases, and mostly rural areas.
It seems that, the higher the voltage, the better the earth is at being an effective conductor.
kwired
Electron manager
- Location
- NE Nebraska
Right on, if you tried to use earth as a conductor even between ground rods only a few feet apart the resistance is likely too high for any reliable operation of any system of 600 volts or less.
A few years ago when we had big ice storm take down many miles of lines and poles, they did not always put the (primary) neutral back up right away because the system would operate without it, the earth was their neutral. This allowed them to get customers back on a little quicker and come back and put the neutrals up sometime later.
ARTICLE 100 Page 70-27 Grounded Conductor. A system or circuit conductor that is intentionally grounded.
Does that not mean Grounded to Earth??
ARTICLE 100 PAGE 70-27 Ground . The Earth
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ericsherman37
Senior Member
- Location
- Oregon Coast
Yeah, but for our regular ol' electrical services the Earth isn't used as a return path to the source. As far as I know, we intentionally ground a conductor for things like lightning and system stabilization and stuff.
broadgage
Senior Member
- Location
- London, England
The general mass of earth, as distinct from an earthed or grounded conductor, was never AFAIK, used as a current carrying conductor at utilisation voltages.
The resistance would be too great leading to excessive power loss and variation of voltage.
"Ingenious" persons did sometimes use an earth/ground return when supplying a single distant lamp, for example at the end of a long driveway.
For high voltage, low current, long distance circuits, an earth return can be used and sometimes is.
Over a long distance the resistance of an earth return is often less than a copper wire.
It is generally accepted that the general mass of earth has effectively zero resistance. The problem occurs when trying to make a connection to the earth, any feasible design of earth/ground rod has a very limited surface area, and therefore results in a high resistance connection.
Put another way, suppose that you drive 2 typical ground rods 100 yards apart, and measure the resistance between them. Typical result might be 25 ohms.
Now drive a similar pair of ground rods 100 miles apart and again measure the resistance between them, it will be the same at say 25 ohms.
No one would use the rods 100 yards apart as part of a power circuit, 25 ohms would result in a very considerable loss, 100 yards of thin copper wire would have a much lower resistance and be very cheap.
If however power had to be transmitted over 100 miles at high voltage, then use of a single conductor with an earth return is worthwhile.
100 miles of neutral or return conductor would likely have a resistance greater than 25 ohms, therefore the earth return is actually more efficient than a second copper wire, and very much cheaper.
In practice a more elaborate structure than a single residential type earth rod would be used, and the resistance might be 10 ohms or less.
An earth/ground return was the norm in early telephone and telegraph systems, and is still sometimes used.
Over a dozen miles or more, the earth return was cheaper and of lower resistance than a second copper wire.
The resistance would be too great leading to excessive power loss and variation of voltage.
"Ingenious" persons did sometimes use an earth/ground return when supplying a single distant lamp, for example at the end of a long driveway.
For high voltage, low current, long distance circuits, an earth return can be used and sometimes is.
Over a long distance the resistance of an earth return is often less than a copper wire.
It is generally accepted that the general mass of earth has effectively zero resistance. The problem occurs when trying to make a connection to the earth, any feasible design of earth/ground rod has a very limited surface area, and therefore results in a high resistance connection.
Put another way, suppose that you drive 2 typical ground rods 100 yards apart, and measure the resistance between them. Typical result might be 25 ohms.
Now drive a similar pair of ground rods 100 miles apart and again measure the resistance between them, it will be the same at say 25 ohms.
No one would use the rods 100 yards apart as part of a power circuit, 25 ohms would result in a very considerable loss, 100 yards of thin copper wire would have a much lower resistance and be very cheap.
If however power had to be transmitted over 100 miles at high voltage, then use of a single conductor with an earth return is worthwhile.
100 miles of neutral or return conductor would likely have a resistance greater than 25 ohms, therefore the earth return is actually more efficient than a second copper wire, and very much cheaper.
In practice a more elaborate structure than a single residential type earth rod would be used, and the resistance might be 10 ohms or less.
An earth/ground return was the norm in early telephone and telegraph systems, and is still sometimes used.
Over a dozen miles or more, the earth return was cheaper and of lower resistance than a second copper wire.
ARTICLE 100 Page 70-27 Grounded Conductor. A system or circuit conductor that is intentionally grounded.
Does that not mean Grounded to Earth??
ARTICLE 100 PAGE 70-27 Ground . The Earth
Article 250.4(A)(5), last sentence: The earth shall not be considered as an effective ground-fault current path.
If a ground fault cannot travel through the earth effectively, a normal current won't either.
ericsherman37
Senior Member
- Location
- Oregon Coast
Wow this is some very cool info. Do you have a source or reference I can look for? I'd like to bring this topic up as a discussion with my apprentices in class as a "food for thought" kind of thing.
broadgage
Senior Member
- Location
- London, England
I dont have any specific source or reference, old textbooks on telegraph equipment would contain references to an earth return, and probably contain details as to the resistance achieved.
I believe that the first trans-atlantic telegraph cable was a single insulated wire, with a resistance of some thousands of ohms. The earth return would have been a few hundred ohms with a basic earth rod each end, and as low as a few ohms with a larger more elaborate structure.
As regards the modern use of an earth return for high voltage power circuits, perhaps it might be worth approaching a utility who use this system.
They would have figures as regards the actual resistance over long distances, which would demonstrate that the resistance is a function of the size and type of earth electrode and the soil conditions, and not related to the distance.
Slightly O/T but a barrier to rural electricification in the USA was the number of rural telephone networks with single wire earth return circuits.
It was feared that use of utility supplied electric power would result in currents through the earth, and that these currents would interfere with single wire telephone circuits.
In some cases the phone companies expected the REA to pay for "metalization" of telephone lines, that is changing to a 2 wire system with a metallic conductor instead of the earth return.
In practice the interfence was seldom objectionable.
I believe that the first trans-atlantic telegraph cable was a single insulated wire, with a resistance of some thousands of ohms. The earth return would have been a few hundred ohms with a basic earth rod each end, and as low as a few ohms with a larger more elaborate structure.
As regards the modern use of an earth return for high voltage power circuits, perhaps it might be worth approaching a utility who use this system.
They would have figures as regards the actual resistance over long distances, which would demonstrate that the resistance is a function of the size and type of earth electrode and the soil conditions, and not related to the distance.
Slightly O/T but a barrier to rural electricification in the USA was the number of rural telephone networks with single wire earth return circuits.
It was feared that use of utility supplied electric power would result in currents through the earth, and that these currents would interfere with single wire telephone circuits.
In some cases the phone companies expected the REA to pay for "metalization" of telephone lines, that is changing to a 2 wire system with a metallic conductor instead of the earth return.
In practice the interfence was seldom objectionable.
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broadgage
Senior Member
- Location
- London, England
Cows are vulnerable to earth currents, they dont wear shoes and theire feet are some distance apart, in contact with the often wet or muddy ground.
Therefore any significant voltage gradient in the ground would result in the hind and fore feet of the cow being at different voltages.
In extreme cases the animal would be killed, though ill health and poor milk production may be more likely.
SWER is unlikely to be a problem unless the cows are very close to one of the earth rods.
Even a few dozen feet away, the voltage gradient will be minute.
SWER systems are normaly at relatively low currents, often 10 amps or less.
10 amps at 132KV is enough for numerous villages or a small town.
The low current limits the voltage gradients.
Of greater concern would be defective installations in farms.
Consider a cow barn with a high resistance or missing neutral in the feeder. many amps will "try" to return to the source via metal water pipes, metal fences, building frames and the like.
Cows and other livestock have been killed thus.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Just to mention it, this is also what paralyzes swimmers in electrified water.
zog
Senior Member
- Location
- Charlotte, NC
And what made Tesla's magic lighting system work, the one where he lit bulbs shoved in the ground in the middle of a field with no wires at all.
ericsherman37
Senior Member
- Location
- Oregon Coast
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