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Underground Wiring: Finding the Breaks

Greg Mitchell | Miscellaneous

The telephone rings . . . Mrs. Jones is calling with an urgent request for service. “We just put in some new flower beds, and now the sprinkler system won’t come on at all. But it worked just fine yesterday,” she says.

Another typical scenario might be when a regular customer calls in the early spring, and complains, “The front yard sprinklers work fine, but in the backyard where you fixed that valve last summer . . . nothing will come on at all.”

Now, the chance of all three of those valves failing at the same time is very unlikely, especially since we know that one of them has been recently rebuilt.

“Have you done any excavation, planting, or cultivation since the last time you ran the sprinklers?” He might answer: “No . . . nothing. And besides we haven’t run the sprinklers at all for two or three months.” You could follow up with: “No construction? Posts? Stakes? Digging of any kind?” Then you can visualize the lights coming on in his head as he replies, ”Well, we did have a new fence put up in January. They broke one pipe by the gate but they fixed that . . . I made sure of it. But come to think of it, we haven’t run the sprinklers since then, until today.”

This should send up red flags immediately in the mind of the irrigation professional. Cultivation, excavation, and possibly edging installation occurred prior to the malfunction. Other damage to pipes may have occurred inadvertently as well. If the control valves can be located and opened manually, wire damage may often be found in the same location.

Underground control wiring which has been disturbed by excavation, such as planting trees and shrubs, cultivating beds, setting fence posts or installing steel-staked bed edging, can be traced to the intersecting point, excavated and repaired easily.

Some of the more difficult and frustrating wiring problems can be attributed to reduced conductivity, (increased electrical resistance), through components of the subsurface control system. That is, conductive deterioration of wire, splices, or solenoids, due to age, damage, corrosion, or a combination of two or more of these factors.

Frequently, splices connecting field wires to solenoid wires corrode and become non-conductive, or reduce current to a level insufficient to activate the solenoid. This is usually due to “improper” splices; more specifically, splices made in a manner, or with materials or connectors, which are not intended for underground use. I have also seen “approved” products — installed with extremely shoddy workmanship, such as wires stripped too far back, twisted too tight or too loose or not used as per manufacturer recommendations — which have failed in one or two years. For this reason, I am of the opinion that attention to detail, and quality of workmanship are at least as important as the materials that are used.

Unfortunately, many inappropriate types of wire have been used in many irrigation systems. Most of these other types of wire are not approved for direct burial. This results in premature deterioration and future wiring problems. I, personally, have discovered the use of thermostat wire, speaker wire, telephone wire, and even lamp cord in some systems.

Quality, size (gauge), and type of wire used also determines the longevity and durability of the subsurface control system. Two basic types of wire are generally accepted and approved for use in irrigation systems.

Single conductor, solid core, 14- or 16-gauge insulated wire is widely used. It is very durable, tough, and easy to work with. It is usually available at irrigation supply houses, in just three colors, red, white, and black. Occasionally it is available in more colors. Of course, from a troubleshooting standpoint, color differentiation is useful.

The other frequently-used type of irrigation control wire is heavy-duty, jacketed, multi-conductor wire, which is specifically designed and rated for irrigation and direct burial. It is usually 18-gauge, with each solid core conductor individually insulated in color-coded plastic, bundled within a heavier outer jacket of black plastic. This type of wire comes in 3, 4, 6, 7, 8, 9, 10, 12, and 13 conductor varieties.

There are some handy tools to help you accomplish the task of locating broken wires. Without these tools, finding a broken wire is like finding a needle in a haystack.

A multi-meter should be used to verify that the controller is working properly (power output). You should start by setting the multi-meter function dial to the appropriate function and range position, (a/c voltage/0-200 VAC, or lowest setting.) This is for reading the standard output of most irrigation controllers.
Assuming that the technician has already identified the “trouble” station, or zone (let’s say #3), he should manually activate that zone on the controller (turn it on). He should place the probe leads, touching one to the coinciding terminal (#3), and the other to the “common” terminal on the controller. If the controller is working properly, the meter should read approximately 24-30 volts (a/c). This confirms that the controller has sufficient output, and eliminates it as a possible cause of the problem.

The next step would be to check the continuity of the circuit in question. In order to isolate the circuit from the controller, de-activate the zone (turn it off). Then loosen the terminal connectors and disconnect the zone wire (#3), and the “common” wire. Set the multi-meter function dial to the “resistance” function (ohms; usually represented by the omega symbol), and the lowest range within that function (usually 200). Touch one probe lead to the “common” wire, and the other to zone #3 wire. A “good” reading, for most modern solenoids, is usually between 26 and 48 ohms.

This reading can vary, depending on such factors as brand, age, and condition of solenoid, distance to valve, length of wire, and type of wire used, and even whether two valves may be operated by one zone, wired together in the field. It is often helpful to use comparative data; that is, read the resistance across several “good” zones in order to establish a point of reference for the reading on the “trouble” zone. Remember to disconnect wires from the terminal to insure accurate readings.

Technicians should use numbered, adhesive, wire-marking tape whenever multiple wires are to be disconnected from the controller at the same time. This, of course, is to avoid getting the wires mixed up and out of sequence.

If all the “good” zones read 28 ohms, and the “trouble” zone reads “infinity,” a symbol like an 8 turned sideways, then you have an “open” circuit. That means that the circuit is no longer continuous — it has been “broken” somewhere. This usually confirms a cut wire, a completely non-conductive splice, or occasionally, an “open” circuit (break), inside the coil of the solenoid itself.

If, however, all the “good zones read 28 ohms, and the “trouble” zone reads . . . say, 63 ohms, then that high-resistance reading indicates reduced conductivity in the circuit. High resistance = low current = no solenoid activation. This type of reading can be the result of a “bad” or corroded splice (1 or more), a partially cut, or “nicked” wire, an aged, worn-out solenoid, a wire which has been damaged, (insulation stripped away; bare wire in moist ground), inappropriate wire gone “bad,” or any combination of the above.

If the problem is in the solenoid, or splices at the valve as they frequently are, it should be relatively simple to locate and repair. If it is one of the other possibilities, it may be more difficult.

If all the “good” zones read 28 ohms, and the “trouble” zone reads 3 ohms, you have a short circuit. This is a situation where the path of the current through the circuit has been shortened. The simplest example of a “short” would be the bare “common” wire and zone wire touching together inside the valve box.

In older, electro-mechanical controllers, the fuse would be blown or the reset button would be tripped by a short circuit. Some of the newer electronic controllers have self-diagnostic features, which display an abbreviated diagnosis, such as: #3 short.

A frequent cause for short circuits, in my experience, has been steel stakes, for steel-bed edging driven alongside, or through, control wiring. Often the stake will “skin” the edge of one or more wires, peeling away the insulation and exposing bare wire. Of course, the stake itself, being steel, is a conductor. This can short two or more wires together, a single wire to ground, or cut one or more wires completely.

If two or more zone wires are shorted together, the resulting malfunction could be that any time one of those zones are activated, all those zones run, or just gurgle if there is not enough pressure to run two zones. If one of the “skinned” wires is the common, it may be shorted to one or more zone wires, or to ground.

As stated in the previous article (Irrigation & Green Industry, March 2001), there can be many factors and combinations of factors contributing to a single visible symptom of a malfunctioning sprinkler system. Keeping this in mind, the thorough testing and inspection of the system, after initial repairs are made, is of the utmost importance.

There are several tools that are useful in the diagnosis and location of field wiring problems. We have discussed how the multi-meter can be used at the controller to eliminate and help determine various possibilities. Those possibilities almost always include the chance that the problem is located at or near the “trouble” zone valve. For this reason, knowledge of the location of control valves is very important.

There is rarely a diagram or “as-built” plan available, so the skillful use of a wire-tracker or valve-locator is required. There are several different types of these devices available, in several different price ranges. A wire-tracker is as essential a tool as a shovel, or multi-meter. Some supply houses have wire-trackers available for rent. However, the investment in the purchase of one of these units is quickly recovered, and begins to return dividends!

The valve-locator/wire-tracker can be used to trace the wire path, locate valves, locate splices, and locate damaged wires. The instruction manuals that come with the units are thorough, well written, and illustrated. They describe a variety of ways to connect the devices, and procedures for optimizing their effectiveness. They even instruct the user on how to determine the approximate depth of wires and valves.

A thorough study of the instruction manual, effective application of different connection methods, and hands-on practice are the best ways to gain proficiency in wire-tracing and valve location.

Another useful tool for locating wire damage is the ground fault locator. This extremely sensitive piece of equipment can pinpoint even slight breaks in the wire insulation. Extreme sensitivity to a “FAULT,” (pun intended), as this unit finds everything. Each ground fault located must be repaired before the pulsing signal will generate beyond that point. Sometimes starting at the other end of the circuit, or other methods, can be utilized to expedite the process. However, the wire-tracker must be used first to plot, and flag or paint, the wire path. An experienced and practiced technician can usually locate most wiring inconsistencies with a wire-tracker. He is able to detect and interpret subtle changes in the audio tone or signal strength that indicate “clues” to solving most locating mysteries. Also, a high degree of persistence (stubbornness) is occasionally required.

Other handy tools like a battery-powered portable solenoid activator, a wire identification probe, or a remote control can save lots of time and steps (walking), while pursuing the elusive “ghosts” of irrigation wiring problems.

If you are returning to a site frequently to repair broken wires because they are old, deteriorated and/or inappropriate wire was used, it might be wiser and less expensive in the long run to re-wire the entire system. New wire insures reliability and can be guaranteed.

April 2001

 
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