TDR, fault finding, test pictures

Discussion in 'Landscape Lighting' started by 1idejim, Oct 28, 2010.

  1. 1idejim

    1idejim LawnSite Fanatic
    Posts: 9,340

    i have a few pictures of TDR tests, how to find the faulted wire and the method of locating a fault without first locating the wire path.

    first set is how i determine which wire in a pair is faulted.

    1. with the dmm set to 2000k ohms insert the black probe directly into the ground (you may have to wet the ground in the summer, don't make mud) and zero out the dmm and de-energize the wire path (just touch both wires together.

    2. touch the red probe to each wire separately, the non-compromised wire should read ol, the faulted wire will have some readable resistance and depending upon the severity of the fault and the conductivity of the soil could actually read continuity.

    it's that simple

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    100_1119.jpg
     
  2. 1idejim

    1idejim LawnSite Fanatic
    Posts: 9,340

    1. reading of 29'0 short

    2. calibration of V.O.P. 55%

    3. actual measurement

    4. this was more of a test i had been wanting to do to find out what the TDR would do with 2 totally different wires, it actually read the accurate one way distance to a short, unusual do to the testing and work we have been doing with irrigation has been a looped reading on a zone valve which would have been twice the distance.

    i have been using the TDR for almost 10 years and i am learning something every time i use it.

    btw the actual length of the wire is 30'

    100_1105.jpg

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    100_1114.jpg
     
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  3. Pro-Scapes

    Pro-Scapes LawnSite Platinum Member
    Posts: 4,181

    I have always taken this for granted. I was taught this many years ago but I am in the practice that if a cable is comprimised it usually needs to be replaced becuause I cannot vouch for the performance of that cable once its been damaged.

    There are of course exceptions to this
     
  4. Prolightscaper

    Prolightscaper LawnSite Member
    Posts: 65

    With the cost of cable now it may be prudent to repair in lieu of replace whenever possible and viable.
     
  5. bcg

    bcg LawnSite Bronze Member
    from Tx
    Posts: 1,835

    Obviously, you also need to consider the wire path. A 30' straight run in turf, no question, just replace it. A 150' run that passes under hardscape or some other difficult obstacle, I'm going to make a real effort to repair first.
     
  6. David Gretzmier

    David Gretzmier LawnSite Gold Member
    Posts: 3,645

    once you find the break, I cut back til I see all pure clean copper. then I replace. often times, you never find good clean copper. it may get cleaner, but I keep cutting til all black is gone. it never ceases to amaze me how far copper corrosion can go inside wire insulation, literally hundreds of feet.
     
  7. INTEGRA Bespoke Lighting

    INTEGRA Bespoke Lighting LawnSite Platinum Member
    Posts: 4,102

    I am not sure that using these tools and techniques to find a 'ground fault' is all that efficient. Time is money right?

    Yesterday I was called out to a job where the "lights are not coming on". Spent 10 mins diagnosing the situation. Found that the maintenance guy had just aerated the "lawns". (Soils are very shallow here and filled with tree roots) One of the LV circuit wires that fed the relay between Zone 1 and Zone 2 had obviously been cut or damaged. Sure enough none of the 3 fixtures on that circuit were alive and the rest were. Pulled the wire out of the ground, found the break, cut back to clean copper, spliced, and slit trenched the wire back in the ground. Time on the repair? 10 minutes. Total time on site = 20 Mins. Materials used = 2' of 12/2 and 4 connectors.

    How long would I have spent there had I gone searching with different meters, then analyzing the readings, then uncovering the wire hopefully where the meter told me the fault was, etc? (not to mention the cost of the meters that would have to be amortized into the cost of the service call) Sometimes the 'brute force' method is the most efficient and most cost effective. Even if I had opted to replace the entire 50 or 60 feet of 12/2 it would only have cost a few bucks.

    I do have a cable locater, and it comes in handy once or twice a year. (Generally when a circuit has been sheared off by excavator equipment and you cannot find the "other end"). But generally we just use a logical, stepwise system of diagnosis and then pull the wire out between point A and B.
     
  8. Pro-Scapes

    Pro-Scapes LawnSite Platinum Member
    Posts: 4,181

    We cut an irrigation wire on the project we are working on now. 8 strand. Distance to timer about 150 ft. Distance to valve box (3 valves inside and thats all this wire was feeding) about 40 ft. My brother was with me and he wanted to grab a foot of wire and splice it back up.

    I said no and wanted to put a box in the ground near the conduit of the driveway and then splice it and replace the 40 ft to the valve. He tried it his way and there was at least 2 more cuts between the first one and the valves. My reasoning was Splice is in a box and we care confident the cable is intact. I would hate to be called back a couple mo later because he thinks we messed up his irrigation and I am getting erratic or intermittant problems with his wiring.

    His time spent messing with it trying to find problems was 2 hours. My time spent replacing it after I took over... 30-40 min plus now I know the area we were in is intact.

    James, with your areated lawn. How can you be sure there are not nicks or other comprimises in your cable. Areation damage is automatic replacement at LEAST across the area it was done in. . I dont care if i will be in and out in 20 min or 4 hours.
     
  9. INTEGRA Bespoke Lighting

    INTEGRA Bespoke Lighting LawnSite Platinum Member
    Posts: 4,102

    Billy. I pulled the entire 50 - 60' of wire out of the ground. It was only hit in one place.
     
  10. Pro-Scapes

    Pro-Scapes LawnSite Platinum Member
    Posts: 4,181

    You...arrived on site... located cut...pulled 50 to 60 ft of wire up. Repaired and reburied in 20 min ?:confused:
     

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