After about 20 years of being a horse owner, something strange happened to me recently. This winter, a day after hooking up the de-icer for the horse water trough, I saw the horses standing at the trough licking their lips with desire but not drinking. After a while longer, they were still there. I've used the simple submerged type of de-icing water trough heaters for many years, and they have gone bad and stopped heating, but I've never had a problem with them introducing voltage to the water trough. In fact, that thought never even occurred to me until this happened.
I tested the water for voltage with my multi-meter by stabbing one probe into the wet soil and the other into the water. It read about 1.5 volts. That's isn't a lot of electricity, but it's certainly enough to make the horses stop drinking... obviously.
I tested the outdoor receptacle and got some strange reading of apparent stray voltage. I decided to replace the receptacle, thinking maybe it was bad after being exposed to extreme temperatures and humidity for 14 years. The new receptacle didn't improve anything. Then I examined the circuit all the way back to the panel in the house... everything looked good. I called the manufacturer of the de-icer and was practically cut-off mid-sentence when I mentioned that I have an electric fence. I was told to drive a grounding rod into the earth near the water trough and connect a copper wire to it and then connect it to the trough to ground it. The company representative promised the electricity in the water would drain through that and everything would be fine. I did just that, and it changed nothing.
I tested the heater in a bucket of water using other receptacles that were actually installed at the house. Same 1.5 volts going through the water. That eliminated the theory that the cause was some anomaly with the fence/trough receptacle.
After much research on internet forums, I learned that 1) I'm not the only one to experience this and 2) it seems to baffle a lot of folks, from owners of one or two horses all the way to big dairy operations. I read all kinds of complicated proposed solutions from building an "equipotential pad" on which the animals must stand to drink (expensive & complicated) to having the utility company install a "neutral isolation" device. I came across one forum post that sounded almost too simple to be true, but had a ring of logic to it. This person originally found this tip in the 10/2014 post on the Henry Milker blog, which is no longer active, but at the time of this post can be found in the way back machine here. The solution? Plug the three-pronged de-icer into a 3-prong-to-2-prong electrical plug adapter with a metal grounding tab. Connect the grounding tab on the adapter to a copper wire that is connected to the grounding rod that is driven into the ground near the water trough. Plug it all in. The grounding wire going directly to the grounding rod provides a strong and close connection to earth ground right where it is needed. I can't provide any more technical explanation than that. In fact, a professional electrician friend of mine struggled to explain a lot of this whole problem. The important thing is that it works. When I tested the water with the de-icer installed this way, the voltage in the water was zero.
If you can shed light on any of this from an authoritative, technical point of view, please do. Meanwhile, I won't have to break ice this winter. Now I just need to convince the horses that it's safe to drink the water again.
