So ( trust me this is doing some good Micheal and thanks for playing along )…so can you explain WHEN the earth might provide a good enough path to clear a fault…and which fault might it clear?
OK…Mr. Whitt…jump in anytime…
If we are speaking of residential, A fault between any ungrounded conductors and metalic piping systems that are properly bonded to the grounded conductor would clear the OCPD. This would also be true of any structural components that are correctly bonded.
If we are speaking of earth as in soil or water, the fault between the ungrounded conductors and the earth would need to be sufficiently close to the point of earth reference to pass enough current to open the OCPD.
micheal…i know what bonding is fella…lol…but thanks for that first part.
AS for the second…the only time EARTH would be a good enough path to clear a fault is on the utility side of the service…where the higher the voltage is present.
The when dealing with Higher Voltage as in utliity lines it uses a multigrounded system and does use the earth as a path…as well as aid it in the ability to clear a fault on there end…
i.e. 120V/25 Ohms = 4.8 Amps where as lets say 14.4KV/25 Ohms = 576 Amps…chances are it will clear the fuse at the pole on higher voltage with an earth impedance of at best case 25 ohms…yeah I will use ohms as everyone already knows that term…
So basically the earth cant be used at all as an effective fault current path in regards to the dwelling or non-dwelling for that matter…but it does play a role in the utilities scheme of things…and it goes even more in depth but you get the picture.
OH…and just for reference…the earth and that reference ( which is back at the source ) is never going to be really that close in residential terms…
ADDED INFORMATION:
I probably should have added that even the more common 7.2KV would give us 288A and would clear the 5A fuse link at the pole…
Yep:-)
Let’s carry it one step more;
How does an electric fence work?
One wire to the fence, the other to a ground rod but an animal 1500 feet away from the ground rod gets schocked.
Your turn Mike…I only deal in Electronic Fences…thehehehe
ok…I cheated…here you gooooooooo
One-touch service
Touch an electric fence once and you’ll know why it works; it’s not very painful – about the equivalent of a sharp slap – but you’ll remember the sensation, and you won’t want to repeat it anytime soon. Horses, too, learn quickly that they don’t want to bump, push through, rub against or chew on electric fences.
How an electric fence works isn’t too complicated either. Every electric fence includes three basic components:
- A wire fence carries an electric charge. This is the “hot,” above-ground part of the system.
- An energizer (also known as a charger) pushes power through the fence. To meet safety standards, most systems deliver power in a series of pulses, usually about one per second. That time between pulses helps the animal to break free of the fence. (A continuous current might cause the animal to “lock on,” unable to let go.)
- A ground system, usually a series of metal rods sunk into the earth and connected to the energizer via a ground wire, waits dormant until the fence is touched by any animal that is also in contact with the ground. The ground system attracts the charge through the animal and returns the current to the energizer through the ground wire.
The system operates on a very simple principle: Electricity will only travel through a closed circuit. The fence wire, energizer and ground rods are three parts of a circuit waiting to be closed; when a horse touches the wire, he closes the gap, and – assuming nothing blocks or impedes the flow of electricity – a surge of current will travel through him from the fence to the rods planted in the ground. Once the circuit is complete, the animal will feel a shock that is likely to discourage him from touching the fence again.
The strength of the shock depends on several variables, but two basic terms in combination will determine the strength of a fence:
- Voltage, measured in volts (V) or kilovolts (kV), is the force or pressure with which a current flows through the circuit. The higher the voltage, the farther the current can travel through the wire before resistance slows it down; higher voltage also causes a stronger “startle” from the shock.
- Amperage (amps) measures the magnitude or strength of the current. The higher the amperage, the greater the sensation the current will cause when it enters a body.
The level of unpleasantness produced by a shock depends more on the amperage – or size – than on the voltage – or pressure – of a current. One easy way to think of it is to imagine the power of water rushing through a fire hose. If you were on the receiving end of a blast of water that raced through a one-inch-thick hose at 100 mph, you’d feel like you’d been struck by a major-league fastball; the impact would probably knock you down. Reduce the size of the hose to an eighth of an inch thick, and you’d feel a sharp sting – enough to catch your attention – but no serious injury. However, slow the water down to only 1 mph, and even a very large hose would do you no harm.
Likewise, a large charge traveling at a very slow rate can actually produce a fairly mild shock. For instance, when you walk across a carpet and touch a doorknob, the shock you feel may be as much as 5,000 volts, but it has a very low amperage. At the opposite extreme, an electric chair operates on only about 2,000 volts, but the high amperage is enough to kill.
With an electric fence, the goal is to sting or startle the animal without causing harm, so electric fences operate with low amperage and higher voltage. As long as the amperage is adequate, horses can be controlled with as little as 2,000 volts, but to make the fence more memorable and easier to maintain, a minimum of 3,000 volts is recommended.
Animals are the intended targets of electric fences, but anything else that comes in contact with both fence and ground will also complete the circuit. Very small items, such as blades of grass, allow a small amount of power to travel from the fence to the ground rods, but not enough to drain the entire system. (It’s like a series of small holes in the fire hose, allowing some of the water to dribble away, weakening the pressure in the hose.) A short circuit occurs when an object, such as a fallen tree limb, reroutes all of the power from the fence to the ground system. Beyond the tree limb, the charge left in the fence is reduced to zero.
I’ll answer yes, let’s qualify that for a moment, stray voltage, current, surges, etc. are trying to get to earth as quickly as possible, No?
I think it finds other things to fry and destroy while trying to make its way back to earth. The better the grounding and bonding systems throughout the structure the better.
now I know after all these posts you are not going to say " Current" is trying to get to the earth…and you will need to qualify surges…because if you are speaking of lightning surges…yes…line surges NOPE…never trying to get to earth…never…never…never.
Here this is better than what i could write:
Stray voltage from intentional actions. The U.S. Department of Agriculture Publication 696 defines stray voltage as “a small voltage (less than 10 V) that can develop between two possible contact points.” Contact points are generally considered to be points close enough between the voltage source and a remote earth path that would allow a current to flow through any human, animal or other object that contacts both points simultaneously. Another important note about Publication 696 is that the document summary states: “While stray voltage cannot totally be eliminated, it can certainly be reduced to an acceptable level.” While this definition focuses primarily on NEV sources, which result from the intentional grounding of the power system neutral conductor, many cases have been identified where improper wiring and load faults on the customer side of the meter contribute to the measured voltages.
Stray voltage from unintentional actions. The New York Public Utility Commission uses the term “stray voltage” to describe the unintentional or accidental energization of manhole covers, street lamps and other urban street-level metallic objects. This definition focuses on MOEV sources such as contact with the power system phase conductor, or in some cases as the result of induced voltages from electric fields.
While the previous two definitions have created some confusion, the common element is that stray voltage could be considered an undesirable voltage potential across any two points that can be simultaneously contacted by an animal or a human. In summary, to develop a stray voltage we can consider the following sources: 1) currents flowing on primary and secondary neutral conductors; 2) faulted-phase conductors; and 3) induced voltages from currents flowing through power lines.
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Stray voltage
As generally defined by utility engineers, stray voltage refers to the persistent voltage imposed on the distribution primary neutral. Stray voltages are mostly due to return currents from unbalanced loads. This is a normal condition of a four-wire, multi-grounded system. In the context of the last 40 years, this voltage is associated with problems in dairy farms and, generally, the voltages do not exceed about 8 V. Stray voltages are not lethal.
Nice piece on Stray Voltage in case anyone wanted to read it…not sure why I posted this but oh well…HERE
There’s no such thing as stray voltage. All the voltage is exactly where it’s supposed to be. After all, there has been no new electricity generated since 1937.
“Where Does Electricity Go?” video.](http://www.youtube.com/watch?v=zFN0wqUIY6o&eurl)
lol…that would be LOST voltage…lol…the IEEE actaully has a definition for Stray Voltage…lol
How on earth did we get in the topic of stray voltage…alas…voodoo witchcraft is not allowed at NACHI
Little volt’s that have lost their way…become a stray until which time they are united again another day.
I’m looking forward to having you as our CMI guest speaker/educator for the October online educational meeting. We’ll have a blast and learn some stuff to boot!