Sunday, May 24, 2020

Proof-of-concept trial

The short. A bare wire touching a steel fence post that is jammed into the ground. The problem is very visible in this image. It is much harder to find when the wire and the posts are rusty or a scrap of old wire that looks like a twig got pushed into a hot-wire somewhere.

An eight second video showing what was happening at the diagnostic disconnect.

I was not very clear about how this disconnect is to be implemented.

Suppose you have a mile of perimeter fence in various stages of repair. Also suppose that the perimeter fence is composed of five different wires.

The genius who installed it has a neutral bottom wire made of barbed, a hot smooth wire, a neutral barbed third wire and a hot fourth and top wire. Suppose the bottom wires are close together to deter coyotes and dogs from scooting under or through the fence.

Suppose the paddock divisions are two miles of single, hot wire but it is mounted on flimsy posts or with posts and super-long intervals.

When your energizer informs you that you have a short, you have over a mile of perimeter fence to walk and two miles of paddock division wire to walk and you might not see it the first time. You have to inspect five miles of wire.

The way I envision these gizmos being used is to use the top wire as the "power bus". The top wire is typically the wire most resistant to picking up ground trash or tangling with another wire. That is, it is the wire LEAST likely to have the short.

The other wires will be fed from the power-bus wire.

Conceptually, you want to break the fence into separate runs of approximately the same degree of risk-for-of-shorting.

The wires with the highest risk of shorting...the first hot wire with a neutral barbed wire above and below it...would be broken into shorter runs and each run would have a single feed through one of these diagnostic gizmos. So if you had a mile of perimeter fence you might break up the bottom wire into four, discrete runs.

For runs that are a lower risk of shorting...the paddock divisions and the middle hot wire in the hypothetical five-wire might feed the entire run through their own unique diagnostic gizmo.

So, on that night when you have a short you can drop out the middle wire.  Was the short in the middle wire? NOPE! Great.

Is the short in the paddock divisions? Drop out that diagnostic gizmo. No sparks? Good!

Then, you would walk the perimeter of the fence and drop out the run of bottom wire one section at a time until you found the run that "sparked" or ticked. You found the run of fence with your problem.

Without some diagnostic method you have five miles of wire to inspect. With the diagnostic, the worst you will have is two miles if it is in the paddock divisions and that wire is usually very visible.

Let me tell you, your ability to find a short is 100 times better when you KNOW it is in a specific 1/4 mile run of fence than when you are racing around looking at five miles of fence where it might be.

The only way to do it by checking voltage is to drop out the run and check the main fence to see if the voltage got higher. You are trying to follow current, not measure voltage.


  1. Interesting way to do it. I was having a problem following you for awhile but I got it now. One way I used when I was in the business was to go out at night with my most powerful rifle scope and scan the fence. A sparking wire can be seen from a surprisingly long distance away. ---ken

    1. Oooo... I like that. I've found bad plug wires by turning the lights off in the shop and watching for the spark. I never thought about a scope. Thanks.

  2. I like your ingenious way of building a low-cost fault-finder. The one I'm looking at buying from Premier 1 is $101.

  3. Magnetic compass works great for finding short circuits. If you can use a cycling circuit breaker or automatic circuit breaker.
    The high current flow generates a magnetic field around the conductor. Hold the compass close to the wire and watch for it to deflect every time the CB cycles back on. Trace the wire with the compass when the deflection disappears that's where the short is.
    I've used this method many times to locate a short in an automobile. Sure beats pulling all the body parts off to inspect the whole harness.
    Caveat 1. Size your cycling circuit breaker to the smallest conductor in the circuit. You cannot push 30 amps through 30' of 20 GA wire. It will not fit. You can force the current into the conductor but it will damage the insulation. Not enough room in the small insulation for 30 amps AND magical smoke. The amps will fit briefly but then all the magical smoke oozes out and the circuit quits working.
    Caveat 2. I don't know if electric fences rectify the AC to DC or not. I've never used the compass trick on an AC circuit. I don't have an AC cycling circuit breaker. The only ones I've seen are massive kV capacity units on big industrial generators. I suppose a second person could cycle the CB for you.
    Good luck with the fence.

    1. The fence energizer fires a very high, very short duration pulse of voltage into the fence.

      I tried a compass and had no luck.

      I tried little "slides" filled with iron filings with no luck.

      I considered hooking up AC current to the fence and using a 100W light bulb to limit the current to a maximum of about one Amp. Then I could use my current pick-up on my multi-tool to follow the current.

      The disconnect and air-gap is where I ended up.

      I may end up with two disconnects per leg. One for diagnostics and one to drop out the leg so I can de-energize the leg without having to walk all the way back to the barn. It is prudent to de-energize the wire before trying to untangle shorts.

  4. And I'm betting you already have an 'idea' as to where the short is occurring in what section of the fencing based on historic knowledge.

    1. Sometimes I grab my test light because I really want the problem to be somewhere else and I'm just grasping a straw so I don't have to get beat up by the 800 pound gorilla. I usually wind up saying "shut up and fix it Fred, just shut up and fix it.

    2. Yes, it is usually in the lowest wire. But sometimes it is not.

      I am also powering the Widow Sprite's fence and the short can be over there. I have a cut-off so I can drop out her fence when the critters are on my pasture.

      The possibility of the short being on my property or Sprite's complicates things.


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