For those of you in Triple Play, I don’t have to tell you about the problems that can be caused by dirty power. It’s something that comes up in my classes and keeps my phone ringing when I’m not training. One of the most frequent questions is about noise from electric fences. POTs complain of clicking on the line that eventually is proved to a farmer’s electric fence. When the fencer, the device that electrifies the fence, is turned off, the clicking goes away -- proving that the root cause is the electric fence system.

One problem could be the brand or the type of fencer. There are high impedance fencers and low impedance fencers. A high impedance fencer will not function with a ground on the hot wire. Problems can include a broken insulator and a metal post is making contact between the hot wire and ground. The root cause could also be green grass touching the hot wire. The fencer ceases to operate. However, a low impedance fencer will continue to function with a ground on the hot wire.

Fencers operate from around 1,500 VDC to around 10,000 VDC. The 10,000 VDC fencers are meant to be used on 20 to 40 miles of fence, not 50 acres. Replacing the 10,000 VDC low impedance fencer with a 1,500 VDC high impedance fencer will make the noise go away and still keep the cows in. Buy a quality fencer and replace the farmer’s cheap fencer. If that solves the problem let the farmer keep it. It is still less expensive than 10 or 15 repeat reports.

Real-World Example
I recently took one of my classes on a field trip with a goal of chasing down the root cause of a fence problem that affected several customers. Field technicians had been there before and found several problems with this farmer’s fence system, but the problem kept recurring. One field technician found a broken bond and after repairing it, the noise went away. Then it came back. The technicians isolated sections of buried plant, identified sheath faults between pedestals, fixed it and guess what? The noise came back again.

When we went to the remote, we could hear the clicking whether we were off hook with the butt set or on monitor. When we went to the barn where the fencer was hooked up, we found 2 low impedance fencers. The AC outlets in the barn were wired correctly, but the fencer was a two-prong (hot wire and neutral wire) but no ground. The fencers were homemade and housed in ammunition boxes.

We unplugged the first fencer and the clicking was still on the pairs. We unplugged the second fencer and the clicking went away. We plugged in the first box and the clicking was still gone. We swapped fencers and there was no clicking when both fencers were plugged in. When we hung the second fencer on a nail in dry wood we pulled a 4-inch arc to the wood. That $20 fencer was faulty. With no clicking off hook we thought we were home free, but the clicking continued on monitor. We managed to reduce the noise, not eliminate it.

We used the test set and identified impulse noise from the fencing system. We used both a low frequency spectrum analyzer and a high frequency spectrum analyzer to look for impulse noise and there was no specific frequency showing up on the graphs indicating the interfering frequency.

To solve this electric fence problem, both fencers need to be replaced and the fence itself is in dire need of repair. I spoke with the farmer and he stated that he would repair the fence and get new fencers when he could get around to it. He was unconcerned that his neighbors were affected. The noise was also on his phone. When he could hear the clicking, he knew that his electric fence was working and the cows would stay in.

Electric fences interfere with phone service and customers will complain. You will dispatch field technicians time and time again and when you finally find the root cause you will never get your money back that you spent to find the problem. I do know this: If the farmer had to pay for the dispatches he would fix his own fence problems.

Signing off
What are your dirtiest dirty-noise problems? Let me know because I’m sure your fellow technicians can learn from your challenges. Contact me at dmccarty@mccartyinc.com or 831.818.3930. And check out my TALK BACK online column and tell me what you think: http://www.ospmag.com/columnists/mccarty/talkback. As always, thanks for your loyal readership and I love hearing your comments -- especially when I’m wrong!