2 wire repair

Discussion in 'Irrigation' started by Without A Drought, Jul 17, 2012.

  1. Without A Drought

    Without A Drought LawnSite Bronze Member
    Messages: 1,087

    I have 2 sites that run a decoder system. One I installed last year, into this year. Its a dual system running off the Icore timer. i'm growing to like that timer and am happy that it's phasing out the ICC. I had a short message that told me the zone, it turned out to be a bad decoder. not a big issue.

    the other is a 50 zone ACC system that we just took on this year. it's a commercial property that was installed by a residential contractor. The layout is not too bad, but it's fed by a 3/4 supply to a 1" poly main behind a master valve. programming has been a pain in this heat.

    so to the point. i had 2 zones reading short at the timer. i found the zones (on one 2 station decoder) first i disconnected the decoder to the valves and tested the solenoids; they were fine. then with the handheld programmer, checked the decoder, and it wouldn't sync via the induction cup. i disconnected and checked the decoder on its own and it worked fine.

    Then i went to work on the wire. (which is where i kind of got confused) i checked the draw at the next box up the line, and had 1.8ma on one side of that decoder (on both legs), and .05ma on the other side. I had .05ma at the problem decoder too.

    I figured a broken wire somewhere between boxes, which wasnt too far. Initially, i disconnected the wires between boxes and twisted the 2 together at one end and took a resistance reading, OL. i tracked both legs and determined a break under a concrete pad. ran new wire around, reconnected and still shorting.

    long story short, took more resistance readings and determined the break was before the point i had run new wire from (it was a second break). found that break, fixed it and the 2 zones worked fine.

    my question to you 2 wire guys is:

    the difference in the amp reading on either side of the last working decoder led me to believe the splice was bad (which it wasnt). why did i get such a low amp reading before the actual break? (about 4' beyond the last working decoder)

    and, is there something different i should have done? either in order or diagnostics? i think i'm pretty good with electrical, but i feel there is a different way to troubleshoot this.

    i've read the hunter rep's posts on this subject, and he helped a whole lot. i may have missed a step though.
    and i have the 2wire diagnostics class coming up in august.

    that said, this style of wiring is leaps and bounds better than conventional wiring. i don't think i'll ever install another multistrand sytem again.

    thanks for any help.

  2. Sprinkus

    Sprinkus LawnSite Silver Member
    Messages: 2,322

    Here's the ACC decoder troubleshooting guide.

    Chapter seven of this manual may also be helpful.

    I'm having a little trouble understanding exactly what you are saying regarding the tests. The ACC decoders are shown to have a constant 3-5mA draw per single station decoder.
    If I understand your post right the low reading on the wire path before the broken wire just indicates a very low current draw, as the case might be in an open circuit fault. A damaged wire that is in contact with the earth, depending on soil conditions and moisture, would usually show up as a very high current draw.
  3. HunterTekGeek

    HunterTekGeek Sponsor
    Messages: 329

    Regarding the use of the handheld programmer (ICD-HP): If the signal was bad from the controller the decoder will not sync properly with the ICD-HP. Remember, whenever you re-address a decoder from the handheld you MUST cycle the power at the controller.

    Sprinkus or One Eyed Jim might have some different suggestions on the next item involving amps. I find it impossible to read amperage using the native voltage and hertz on the I-Core DUAL when using a clamp meter. Take a 24 VAC transformer and connect the 2-wire path(s) to it. Your milliamp reading should be 8.5 to 10 mA per decoder. Sprinkus is totally correct on the 3.5 mA draw when connected to the controller, but that is a different signal than using a transformer directly. If you try to read this at 35 VAC and 1.2 Hertz (native current on I-Core) it might come out goofy. Tech term.

    In addition, if one side (wire) of the 2-wire path is shorting to ground it will definitely have more milliamps than the other side. There shouldn't be more than a 5% difference between the red and blue (or black and red) wires when things are "tight".

    You said the reading was low BEFORE the break? The reading should be HIGH before the break or short to earth and low on the other side. Make sure you are taking a reading on the actual wire path and not the decoder wires when looking for a leak to ground.

    Again, the key is to carry a 24 VAC transformer that you can plug into a 120 VAC outlet. If no power is available, use a stout inverter off your truck battery. Hope this helps. Let's also see what the other guys say.
  4. Without A Drought

    Without A Drought LawnSite Bronze Member
    Messages: 1,087

    I hadn't tried using a 24v transformer. i will do that in the future as it seems a much more steady source of power.

    my amp reading in the box before the break was approx 1.8mA before the splice, and .05mA after the splice on both legs. (not on the decoder wires) the break was a bad nick on the blue side about 4 feet past the last working box.

    my only guess it that it was a break that was not in contact with the earth, therefore never created an actual short. idk. thankfully it wasn't that long of a run between boxes, and i was able to do some trouble shooting and head scratching without having to do a lot of digging.

    the programmer works great, i think i was just trying to work it in a way it doesn't work.

    i have the 2wire course from the IA in a few weeks, hopefully i can learn a little more. (i've been reading a bunch online too)

    incidentally, on another site, a DUAL site, i've had 2 decoders go bad in the last month or so. anyone have problems with them?

    thanks again for all your help,

  5. Turf Dawg

    Turf Dawg LawnSite Gold Member
    Messages: 3,719

    I took one of the two wire classes from Tucor and thought it was very helpful. I still have a ton to learn, but at least I know what to look for. I was able to get two systems up and working for a bank branch that had the other guys scratching their heads around here.
    Posted via Mobile Device
  6. tonytonick

    tonytonick LawnSite Member
    Messages: 37

    Dear Gentlemen,

    You might find this helpful. I've been teaching this to installers in UK and Western Europe for over 10 years; nearly 100 groups including superintendents. Most professional installers now use this method. It works with virtually any decoder system

    You can easily make your own transformer. 24VAC, about 150VA. Make sure you can ground each side of the 2 wire path with an earth lead and a crocodile clip. The 115VAC line input must be 3 pin with a ground pin. Connect this ground to the transformer metalwork and use this connection to ground one side then the other side of the 2 wire path when finding earth leakage.

    Just make sure it's safe, don't want any 115VAC fatalities!

    Please don't get funny with this posting, I'm not trying to sell you anything, just attempting to be helpful.


    Tony Ware

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