Nobody has been working in my yard. How is it that my wire is cut?
A wire can be nicked or cut with garden and hand tools. Rodents can chew into a plastic casing and sometimes bite through it. Environmental forces can damage a wire in unexpected ways. One of these forces is expansion or contraction of the ground, forcing concrete slabs in driveways, sidewalks and stairs to squash the wire so hard that it pinches it in half. Sun can also damage and crack the plastic casing so that moisture can infiltrate and corrode the wire.
Wire is a metal conductor – Usually it is between 14 to 18 AWG Copper or Copper Clad Steel (either is typically used in the dog fence industry). The wire is highly conductive and subject to rapid corrosion when open to a wet or corrosive environment. Buried and submerged wire are always exposed to moisture that makes ground contact. This makes them more susceptible to corrosion than wire that is attached to above ground fences or laid on the surface in consistently dry conditions.
Tensile strength: Wire can be stretched some before it breaks. A wire’s tensile strength when it is new and in perfect condition is different from when it is older and subjected to conditions which cause deterioration on the metal conductor. If too much metal corrodes away, the line may break under much less stretching force than it might have otherwise at the same temperature and pressures.
Sun exposure to the wire casing can damage non-UV protected wire casing. This damage allows water to penetrate and react with the metal. However, if sun deterioration is occurring, then the wire is probably not in a wet environment, as it is not buried.
Moisture absorbent wire casing – PVC wire casing is not my favorite, for I believe it absorbs and then holds moisture against the wire. This is why we do not use PVC cased wire. We only use HDPE or HMW wire casings.
What happens to a wire over time?
Time – Conditions constantly change over time. Heat, cold, wet, dry, digging, shaking, movement, shovels, rodents chewing, splices, nicks, more dry, more wet. All things are possible given enough time.
An intrusive yard job (Aeration, verticut, sprinkler system installation, outdoor lighting, cable TV lines, etc.) can cut cleanly through a wire, and other times nick or skin a wire. A wire does not heal itself like you or I if we cut our finger or skin our knee. A single nick in a line is bad, as it eventually corrodes given enough time and exposure to moisture in the soil. The oxygen of water binds to the copper and corrosion begins immediately. Eventual corrosion creates a weakness in the wire in that spot. Over time, ground settles then swells again like a big sponge. Expansion puts pressure on a wire, and stretches it. Eventually the stretching wire breaks due to pressures exerted by the pulling forces of the swelling ground around it.
Clean Cuts and Nicks
Multiple nicks in a wire sometimes happen with a single yard aeration or verticut. Sometimes only one nick happens. But, multiple nicks over several years in the same wire are also a distinct possibility. For instance lawn aeration, or burying a CATV or fiber optic line can nick the line multiple times, and maybe even cut it clean thru a time or two.
Clean cuts in yards with just the right amount of moisture in the ground are relatively easy to find for us. But dry the ground out too much, or put too much moisture in the ground and it gets tricky and takes more time.
Clay soils hold moisture longer. Well-drained sandy soils corrode slower than clay soils.
Nicks in the line do not present an immediate problem to the system until the nicks begin to fail in a cascading manner over time. This means that you unplug the fence when the first one fails, then the others may soon fail shortly thereafter. We do not know if the one break is the first of many more to come, or the one and only. Though, with a Volt/Ohm meter, we can generally tell if there are other problems in the yard, such as bad splices. That doesn’t mean we can find the bad splice, only tell that it/they exist.
Wind? Yes, even wind. Wind will dry out a yard when the yard dries out, big cracks can open in the ground. That causes pressure or pulling forces on a line. As moisture content is lowered, then a yard’s soil is less conductive and a bad splice may cease to carry enough current and a wire break alert can sound.
Wind also exacerbates a bad splice situation when the bad splice is near a tree that can move as the tree sways a little. Gentle swaying rocks the ground in the vicinity of the tree. This slight movement shifts the ground around a tiny break, or bad splice. Continuous pulling of the wire just a tiny bit, over and over again can cause a splice to separate, or a nick to break or pull and relax, pull and relax. Connect, disconnect, connect, disconnect.
Lightning strikes near enough to the line are a problem as the high voltage and amperage of lightning can blow bad spots out like a fuse gets blown in your car or home.
Another way a nicked line can affect us is that sometimes after a wire pulls apart and breaks, it can also move back together as the ground shrinks and expands, over and over. The close proximity of the two wire ends and the electrical current in the line carried across a short distance (thanks to moisture and sometimes even high conductivity levels of some soils is sufficient to allow the fence to operate again.
Some waterproof and direct burial wire connectors fail over time due to lightning strikes or the waterproof materials drying out or incomplete submersion of the copper wires into the waterproofing connector gel.
Water – H2O Content of soil aids in the conditions required to cause wire corrosion. Water can also help delay some wire break alerts by conducting electricity thru the moist soils.
Moisture causes expansion and contraction of the soil – Think of a sponge on the counter behind your sink that is sometimes dry and shrunken while other times it is wet and full. Imagine a wire in that sponge that under proper conditions will expand to the size of the sponge. However, damage the wire, and it is subject to breaking under the pressure of expansion.
On the other hand, damage on a wire in a dry area may never become an issue. This may happen if a wire is buried in dry sandy or rocky soil. Well-drained soil allows the moisture to drain away so the wire remains relatively drier, slowing corrosion. A wire stapled to a fence post, chewed on by a rodent may also never fail from corrosion. Also, a damaged wire laid on top of a garden may also not corrode as quickly as one under the mulch or in the dirt.
Acidity Levels and Conductivity
Some soils are more acidic than others, hurrying the corrosion process.
Another factor to consider is the effects of electrolysis. This is where electrons of dissimilar materials will migrate from an area of high concentration to a lower concentration. In the dog fence world, we recognize this effect and are aware that even a bad splice, or open nick or scrape on a wire will fail slowly as long as there is a steady low voltage energy supplied to the wire. However, once that voltage is removed (ie. the wire is cut clean thru and separated, or the unit is unplugged from the power source) then a wire quickly fails, and not only in the spot where it was cut, but in all places with exposure to the environment. Some places will fail quicker than others, depending on the micro-environment of that troubled wire spot. This is why when a wire gets cut we will often find multiple breaks and bad splices during a service call. While you waited three weeks to call because the dog wasn’t leaving the yard yet, or in the two hrs it took us to get there, electrolysis occured and your apparently good wire, suddenly blew up into two or three wire cuts and a few bad splices from the cable or phone company.
Conductivity of soils change as moisture is added. Some soils are more conductive than others. This happens from dissolved fertilizers containing salts. Any concentration of salt creates a corrosive environment. Aqueous saline solutions flowing by chance to, around and thru the vicinity of exposed conductors create potential for invasion of corrosive moisture and materials to the copper wire. A wire loses electrons to the environment. This causes a wire to thin and break or change to a less conductive state, creating a wire break or wire break alert.
Use of fertilizers – Fertilizers increases conductivity of soil and aids in Electrolysis. Electrolysis occurs quicker with higher concentrations of electrolytes in the soil.
Soils that receive fertilizers have more metals and electrolytes in the soil. This allows corrosion to occur more quickly. Add moisture (irrigation systems) to the soil, dissolving the salts, and metals into liquid solutions that penetrate a wire nick or bad splice (wrapped in electrical tape), and the corrosion will occur more quickly.
Acknowledging that a fence with a constant low voltage power supply with a wire/line resistance below the minimum threshold to trigger the wire break alarm corrodes slower than one with the power supply removed at a higher than optimal resistance. What do I mean by that? If you leave your fence plugged in, the bad splices and nicks corrode slowly. On the other hand, if you unplug an otherwise normally operating fence with nicks and bad splices, the lines is exposed to a lower naturally occurring nominal electrical background of the earth. Under this environment, a wire will often deteriorate quickly. Thus, a fence left energized, albeit in a state of high resistance will generally not trigger a wire break alert for much longer than one left unplugged.
This theory is important because once a fence fails from one event, by the time we get it fixed, we often find many old damaged areas that have failed at nearly the same time, or shortly thereafter, and for weeks and months after the main disruption. We always hear the same thing from our customers… “You were just out here to fix our fence, and it is beeping again.” Now, re-read that statement this way: “you didn’t fix my fence”.
Bad splices are the crux of many service calls. This creates an intermittent situation where the fence will work for a while, then stop, then start, then stop. This happens when an improperly spliced line gets moisture into the splice causing corrosion between the two wires. Corrosion creates resistance and weakness in the line. High resistance causes a wire break alarm to trip, and the weakness of the splice can cause it to pull apart.
When we suspect that the line will fail again because of high Ohm readings, or fluctuating readings caused by bad splices or shifting ground around broken wires, we will inform the homeowner that they will be calling us again. Sometimes that can happen before we can get out of the neighborhood. Other times it takes hours, or years.
A succession of breaks is very frustrating for a homeowner. They always want to blame us for not fixing it right the first time. This is why we offer to go back for free to check our work. We expect with 99% certainty that we will find another break or another bad splice that someone else made before us. When we find someone else’s bad splice or another break we charge again for our service.
When wires fail from nicks and bad splices in the wire, a customer can usually count on seeing us multiple times before we can work all of the bad spots out. Each trip will cost the owner money again and again. Those multiple trips usually upset a customer and stress our relationship with them. But we cannot find things that are not CUT all the way thru. Consequently, all we can do is respond to your next requests for service. We ask that you remain patient with us as we gradually work our way thru each repair until it finally quits breaking again someday.