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Is Two-Wire Too Good to be True?

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In most cases, utilizing a new or different product isn't about simply going out and buying it. That would be easy. The real challenge lies in learning what it is, what it does, how it works, and then training your crews to operate it proficiently.

For example, a faster riding mower sounds great in theory, but if your crews are only familiar with walk-behinds, your brand new, faster mower may actually make your crews less productive at first. Naturally, in time, they?ll learn to operate it, and your increased productivity will kick in eventually. In fact, it may only take a week or two for that mower to begin paying for itself. But wouldn't it be great if you could get all the benefits of the new mower, without sacrificing the familiarity and ease of the old?

With some products, you can. You've probably seen numerous articles published of late about two-wire irrigation technology. It's been touted as everything from the savior of the copper shortage to the savior of the labor shortage. Manufacturers aren't just blowing smoke, either: two-wire really does have significant benefits on some properties.

However, if you've spent the last five, ten, fifteen, or even fifty years installing conventional irrigation systems, you're probably loathe to move away from them, and rightly so. Who wants to learn an entirely new controller, despite its advantages, when you've come to know the old controller like the back of your hand and could probably program it in your sleep?

Manufacturers completely understand this reluctance, and to make two-wire even more attractive to contractors, have gone beyond making only controllers. They'?re also manufacturing universal add-on units that can convert any controller to two-wire output. You can continue using the same controller you've come to know, and not have to worry about learning the ins and outs of all new programming, and still enjoy two-wire's many benefits.

However, two-wire is useful for more than just new installations. Its ability to work hand-in-hand with conventional controllers means that it can also be ideal for system expansions.

"Two-wire can represent a golden opportunity that can save thousands of dollars when expanding existing, conventional systems," says George Cook, vice president, HIT Products, Lindsay, California. "If the on-site parameters are fit for a two-wire application, what would have been a difficult expansion can become a fairly simple one."

"When my supplier explained the process of adding two-wire onto an existing system, it almost sounded too good to be true," says Chris Himes, director of purchasing for Norman's Nursery, San Gabriel, California. "Then I used it to expand a system myself, and saw first-hand how easy and cost-effective it is."

4_2.jpgMore with less

Of course, before you even begin to consider expanding an existing system with two-wire technology, you need to understand exactly what two-wire is. In the most basic terms, two-wire is a way of doing more, with less -- getting more benefits, but using less wire.

In a conventional irrigation application, wire is run from every individual valve all the way back to the controller. For example, imagine a football field. The controller is placed on the home team's goal post. There is a valve at the center of every ten yard line. In a conventional irrigation system, you need ten yards of wire to connect the first valve to the controller, 20 yards of wire to connect the second valve to the controller, and 30 yards of wire to connect the third valve to the controller. That's already 60 yards of wire, and you haven't even hit the halfway mark yet.

In total, you'd need 550 yards of wire to connect each valve to the controller, and at least another 100 for the ground wire, assuming you use the same ground for all of the valves. You'd be using 1,950 feet of wire!

Now, consider what you'd need to wire the same football field using two-wire technology. A football field is 100 yards long. To wire valves down the center of the field every ten yards, you'd need 200 yards of wire -- and that's it. That's a total wire savings of 450 yards, or almost 70%! Factor in the current price of copper, and you can see how significant that savings is. How is it possible? Simple -- two-wire works like beads on a string. The string is the wire, and the beads are the valves. In a conventional system, each bead would dangle from its own individual string, but in a two-wire system, all beads are strung on the same string. The wire runs from one valve, to the next, to the next, just like the string runs from one bead, to the next, to the next.

Each valve is connected to the two wires via a small device in the valve box called a decoder. The controller sends messages down the wire, telling the system when to run, and each decoder turns its valve off or on. In other words, in a typical system, the controller directly controls each valve; in a two-wire system, the decoders directly control each valve. Generally, the cost of the hundreds or thousands of feet of wire a conventional system uses far outweighs the cost of purchasing a decoder for each valve. However, while the cost savings attributed to a two-wire installation are most dramatic on larger properties with numerous valves, savings can be seen on sites with as few as 20 zones.

"The materials decoders are made of -- chips and circuit boards -- have not shot up in price the way copper and wire have, so two-wire is becoming economical for smaller and smaller jobs," says John Fordemwalt, president of Baseline LLC, Boise, Idaho. "Over the last two years, decoder prices have generally remained flat, while the cost of wire has gone up roughly 53%."

5.jpgHowever, the benefits of two-wire aren't just financial; two-wire can also greatly simplify maintenance procedures. "I first learned about two-wire when I was called on to start maintaining some two-wire systems," says Timothy Jacobs, owner of Montgomery Irrigation, Jessup, Maryland. "They're so user-friendly that I started installing them as well."

Getting back to the football field, to wire it the conventional way, you'd need at least 11 wires -- ten for the valves and one for the ground. To save yourself from having to dig multiple trenches, you'll probably bundle all the wires together and bury them in a single trench. To make maintenance easier later, you'll also probably buy 11 different colors and patterns of wire (red for valve one, black for valve two, red with white stripes for valve three, etc.).

Years pass. The wire colors all fade from being in the ground so long. Then, a pipe breaks mid-field. A backhoe goes out to dig it up and repair it, but oops -- the blade cuts through all 11 wires during the excavation. You're going to have a heck of a time figuring out what gets connected back to what. You'll wind up having to test each wire individually to figure out which valve it runs to.

Of course, with only 11 wires, that doesn't sound so bad. But what about a larger application? What if 50 or 100 wires are broken? You couldn't have color-coded them in the beginning anyway -- there wouldn't have been enough colors to go around. In that situation, it could take hours to determine what connects to what. However, if a two-wire system had been initially installed, you'd only have two wires to worry about, vastly streamlining the process.

Start branching out

Another benefit of two-wire is the ability you have to splice and Toff in different directions. If a customer wants to add a new zone in a conventional system, you're going to have to dig all the way back to the controller to lay down the wire. You'll most likely be going through previously landscaped areas, which you'll then have to repair.

If you had a two-wire system, you could simply splice into the two-wire path at any point, connect new wires, and take off in a whole new direction. You'd never have to trench back to the controller. This makes expanding a two-wire system and adding new zones a breeze. "For multiphase developments or for design/build jobs, the ability to change or expand the system merely by extending the two-wire path and connecting more decoders reduces the effort and cost dramatically," Fordemwalt says.

Of course, as a contractor, you could be working on systems that you didn't install. A conventional system might not have been your choice for a particular site, but it was installed years ago, and now you're stuck working with it. The customer wants to expand the system; you know that means it?s time to break out the trencher, right? Not exactly.

Although many do not realize it, two-wire technology can make expanding a conventional system just as easy as expanding a two-wire system. This is accomplished by transforming a small portion of the existing system into a two-wire system, and splicing off into the newly landscaped area from there. Thanks to the universal two-wire add-on units being produced by a variety of manufacturers, the conventional system will work hand-in-hand and side-by-side with the two-wire system, lending contractors the ease of expansion with the familiarity of the existing on-site controller.

It's essentially like grafting a branch of yellow roses onto a red rosebush. You designate a spot on the rosebush that will support the new branch, just as you designate a portion of the existing irrigation system to support the new branch of wires by converting it to two-wire output. Then, you cut into the rosebush, just as you cut into those wires, and graft the new branch in, just as you connect the wires for the new branch of the irrigation system.

The red rosebush provides the grafted branch with water and nutrients in the same way the controller provides information and commands to both the conventional part of the irrigation system, and the new two-wire portion. The red rosebush continues to grow and blossom, just as the conventional part of the system continues to operate as it always has, and the yellow, grafted branch grows and blossoms in tandem, like the two-wire system operating perfectly in conjunction with the conventional system.

An expansion using two-wire is especially useful on applications where trenching back to the controller would be particularly difficult, impractical, and unaesthetic. Wire might need to be run not only through established landscapes, but through a parking lot. This might not only require additional time and labor to trench through, but also additional time and labor to repave afterwards. You may wind up having to hire a subcontractor.

3_13.jpgHowever, if there's already a branch of the existing irrigation system located beyond the parking lot, you can convert that branch to two-wire technology. The system expansion can T-off from there, allowing you to avoid having to dig through the parking lot to get back to the controller.

To get started with an expansion of this kind, you have to have two good wires to work with. The whole point of the effort is to avoid having to lay new wire back to the controller, so you don't want to have to lay down two new wires -- it's not cost-effective. At that point, you might as well just expand the system in the traditional manner.

Generally, you want to choose the two wires that are closest to the area you want to add to. In most cases, if you have two working valves, the hot wire running to each valve can be considered good enough to support a two-wire system. You can also use an Ohm-meter to test for continuity of the wire to ensure that it's useable.

Because the two valves will be the basis of the two-wire portion of the system, both will need decoders. The rest of the conventional system can remain untouched. Even the controller can remain -- all that needs to be done is to add a universal two-wire add-on unit, allowing the existing controller to communicate with the new decoders and valves in the field.

If all of that sounds fairly simple, it is. "Creating a hybrid two-wire system isn't particularly challenging, as long as you have two good wires to start with," says Ed Underhill, president of Underhill International Corporation, Aliso Viejo, California. "Two-wire may seem like a foreign language at first, but after contractors install it once, they find out just how simple it is."

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