Follow the Null Line
The installation may have been easy, but identifying the problem can be difficult. Large residential and commercial sites can be troublesome, especially if the system was installed by another contractor. The good news is that there are tools specifically designed for locating irrigation and landscape lighting electrical problems.
In an irrigation or lighting system, an electrical problem is called a fault. A fault is a break, nick, loop or a point with bad connections/bad splices. A fault can also be a reversal in the wire underground, which causes the system to stop working properly. With the help of a few key wire tracking devices, electrical problems can be quickly and easily located.
Tracking devices have been around for about 30 years, explained Neil Burns, North American utility sales manager for Greenlee, Rockford, Illinois. “A professional contractor will use a wire tracking device every time he has to find a fault unless he knows the site well or was involved in installing the system himself,” Burns noted. Fault-finding devices are a good fit for any maintenance company that frequently works on large residential, commercial or multi-unit complexes, especially if they did not install the original system. “Time is money. Professionals do not want to spend all day on-site trying to find a break,” Burns said. “Using a wire tracking device can help the contractor locate the fault within a short period of time, sometimes even a half hour.”
There are three pieces of wire tracking and fault-finding equipment that irrigation and lighting contractors should keep in their toolboxes. They include a volt ohmmeter, a wire and valve locator and a pulser. Each unit is used in specific situations.
Let’s start with the volt ohmmeter (VOM). A VOM is used to test the clock/controller to make sure 120 volts AC is going into the clock and that 24 volts AC is flowing out of the clock to each zone. Verifying this will rule out any problems that could have been related to the controller itself. The VOM will give you an idea of where to begin looking for an electrical problem.
A VOM measures the ohms, also known as resistance, that is flowing through the wires. Measuring the ohms can determine whether a large or small fault exists. When the ohm reading is small, it means there is a large fault. When the ohm reading is large, it means there is a small fault. Not only will the volt ohmmeter identify a large or a small fault, but it can also point to specific problems. A VOM provides a numerical reading. If the reading is 1-10 ohms, the system has a short. A reading of 12-60 ohms means the system is in good working order. However, if the reading is between 180 and infinity, the system may have one or more of the following faults: bad connections, bad splices, a nicked wire, an open solenoid or a broken wire.
Once the volt ohmmeter has identified that a fault exists, the next step is to use a wire and valve locator. A wire and valve locator unit is designed to help a contractor find an underground wire path. It will also determine how deep the wire was installed and the location of solenoid valves. An experienced technician may be able to also locate wire breaks or large nicks with this unit. “The wire and valve locator helps our crews locate valves, wires and breaks quickly,” said Josh Miller, operations manager for American National, Chicago, Illinois.
The wire and valve locator unit has two pieces, a transmitter and a receiver. The transmitter is used to send out a signal to find or follow the path of a wire. The receiver uses the impulse sent by the transmitter to find the wire path. Depending on the manufacturer, the initial hookup of the equipment may vary, but the way to use the equipment will be the same.
Before trying to find a wire path, the contractor should perform a simple test to make sure the valve locator unit is working correctly. Connecting the red and black lead to one another will point out any problems with the unit itself.
“Low batteries, or missing batteries, is the most common problem contractors have with using a wire locator,” Burns said. “The wire and valve locator is a crew tool that is left on the maintenance trucks and not thought about until they’re needed. If the batteries in the unit are worn down when you start, it can waste a lot of time.”
Once the batteries have been checked, the next step is to establish a good earth ground. When a ground stake is not properly installed, it can affect the accuracy of the fault finding equipment. Climates like those in Arizona can interfere with the accuracy of a ground stake. “In Arizona, on 100 degree days without rain, the ground is so dry that a good enough ground path cannot be established,” Burns commented. “In these situations you have to water the ground first so that a sufficient ground return is established.” Once the unit has been tested, it is now ready for use. To begin, plug the headset into the receiver, turn the unit on and rotate the switch until it reads between 4 and 8. Point the antenna or probe towards the transmitter. You should be able to hear a pulsing noise on the headset. When the headset cord is too close to the receiver antenna or the receiver battery is low, high pitched tones can be heard.
To locate the wire path, walk around the transmitter location with the probe pointed towards the ground. The sounds heard on the headset will indicate what has been found.
A wire path will have a “null” sound, or absence of tone when you are directly over its path. If you move to either side of the wire, the volume of the tone will become louder. Therefore, to track the path of the wire, follow the “null.”
If a signal or “hot spot” is heard over the headset, a fault has been found. When you hear a hot spot, back up until you find where the null turns into a hotspot and mark the ground with marking paint or flags. A hot spot could mean that the system has a nicked wire, a bad splice, a direction change, broken wires or a solenoid valve.
Skilled technicians will be able to use the wire and valve locator to identify the exact location of a fault. However, most will need to use a third piece of equipment once the wire path and depth have been decided with the locator, and that is the pulser. The pulser can be used to pinpoint the exact location and depth of shorts, buried wires, clean breaks and small pinhole-sized nicks. “We keep a pulser on all of our service trucks, along with the wire and valve locator, so that our crews can locate faults quickly,” said Jim Todd with Great Lakes Irrigation, Rochester, New York. “The time we save using these pieces of equipment really adds up.”
A pulser can’t be used to find and track the path of wire, but is used after the wire has been tracked. “Once the wire path has been tracked, spray paint or flag the spot on the ground where you think the break is,” Burns said. “The high impulse from the pulser can be used to point to the break within a " of its actual location.”
While a pulser is used to pinpoint specific problems, certain situations can be problematic. For example, the fault finding equipment may find a “false reversal.” A false reversal is when the broken wire loops around and crosses the ground return. The ground return is the path the voltage takes when moving from the faulted spot in the wire back to the ground stake.
To make sure that you have actually located a fault and not a fault reversal, you can perform a quick test. Above the spot you think a fault may be, divide the location into four even sections. Cross into each section while reading the receiver. When you have located an actual fault, the meter will point into the center of the dial while you are standing in each one of the four areas. However, if the reading does not move to the center of the dial while in each quadrant, then you have found a false reversal and need to continue down the wire path to find the actual fault.
Multiple faults also require additional attention. When a system has more than one fault, it can cause the receiver to reverse each time a fault is found. The largest fault will most likely create the strongest signal on the receiver. The best method for correcting multiple faults is to repair the first one found, re-test and move on to the next fault.
“When we work on systems that have multiple problems, like a cut wire on zone one and bad splices on zones two and three,” Todd explained, “we always fix the first fault we come to and retest it before moving onto the next.”
Like false reversals and multiple faults, a high resistance fault can also be difficult to identify. In most cases, a high resistance fault will produce a very weak signal in the headset. To alleviate this problem, turn the sensitivity knob completely clockwise and retest the area in question. Technicians who frequently use fault finding equipment will admit the process is 80% art and 20% science.
When using any type of equipment to locate an electrical problem, it is important to remember a few things: first, training is key. “We depend on the guys in the crew who know how to use the equipment to teach the others,” Miller said. Each unit is shipped with an operator’s manual, but attending a distributor or manufacturer sponsored training class is the fastest way to learn how to use the equipment. “We host many field day trainings where we actually go out to a site as well as working in the classroom,” Burns said.
Practicing at your office is a good way to familiarize yourself with the equipment. Creating a mini test site with broken wires just under the ground’s surface will give you a chance to practice with the equipment and get used to the way it works.
One of the most frustrating concerns is, if there is an electrical problem, you sure don’t want to tear up the entire area to find the fault. Having tools like these available to you can save time, money and frustration.