Saturday, May 23, 2020

My effort to make it easier to find shorts in my electric fence

This is the prototype of the electric fence disconnect and short-circuit diagnostic.

I intend to proof-of-concept today.

My original intent was to use a neon lamp as the indicator but Mrs ERJ convinced me to try an air gap. Not only does an air gap provide a visual spark, it also generates an audible "SNAP!".

That snap is one reason why some shorts are easy to find while others are difficult. A short that arcs across an air gap can be identified from 100 feet away while you can be looking at a hard, metal-to-metal short and not recognize it.

The snap will also make diagnosis easier on sunny days.

A slightly closer look at the air gap. The blue parts are Gardner Bender 16-14 AWG ring terminals similar to these. Wire was crimped-into-place and then snipped flush with the end of the terminal to create the electrode that (we hope) will generate a spark. Obviously the gap size can be adjusted.

According to this academic paper, the break-down voltage for a 5mm air gap in clean, dry air will be approximately 4000V. 5mm is approximately the thickness of two nickels and one dime.

Beyond proof-of-concept
  • The mounting needs to be figured out.
  • The installation needs to be "ruggedized"
  • The insulated portion of the blade needs to be extended
  • The fence needs to be modified so runs are not doubly and triply connected. The diagnostic only works when there is a single feed into the run


  1. Why not use a spark plug to allow for precise adjustment of gap to tune it to your actual fence voltage and get a reliable response?

    1. Ease of attachment. The ring terminals match the studs.

      On a moist day, with a clean fence, the spark can easily jump 10mm from a barb on the fence to a metal pole. 5mm should be OK even with some weeds touching.

      One variable I don't have a handle on is how much the sound level will change with varying the gap. Sound, as sensed by the human ear and brain, is logrithmic. Whisper-to-shout is roughly 30dB-to-90dB which is a 10^6 difference in magnitude. Pretty amazing that we have that range. The nice thing from a diagnostic standpoint is that the spark gap does not need to be super-loud for the human ear to find it.

    2. I guess you could use a terminal block then have an adjustable machine screw on an 'L' bracket that you can screw in or out to adjust the gap. Just guessing that a smaller screw might make a bigger pop? Surrounding noise, wind etc. might be complications.

      Put it inside a shade box to block direct sunlight, maybe paint the inside flat black - or just use a blanket like the old-style photographers did, that would help with the surrounding noise too. Of course your neighbors might see you out there and think you're a bit - tetched.

  2. great timing on me stumbling across this post, as I am in the middle of installing an anti-raccoon electrification of my vegetable garden - to avoid the unhappy experience of last summer when right before the first harvest, a little bastard trash bandit destroyed the entire crop of 20 or so corn stalks . . .

  3. Premier 1 makes great electric fences for that. We use one with a solar charger.

  4. I'll be interested to see how it works in the field.

  5. I’ve been using a solar powered fence for a while and find it very reliable. As for testing, several beers are needed prior to the old standby of urinating on the suspect section.

    1. One of my co-workers tricked his city-slicker cousins into peeing on the electric fence. They vowed to never do it again.

      Then Buckey's dad bought one of those new-fangled, pulsing models. Buckey practiced so he could discretely lift up the stream in synch with the clicking coming from the barn.

      "Hey guys" Buckey said after he and the cousins had consumed a goodly number of barley-pops "this is fun."

      "Hell no. You got us once" they replied.

      "Don't be a puzzy. The fence is off" Buckey said, discretely lifting the flow.

      "Look, I see a frog...."

      Of course the city-slicker cousins had to stand behind the wire and see if they could hit the frog.

      Buckey got three of them, that time.


Readers who are willing to comment make this a better blog. Civil dialog is a valuable thing.