Articles

What Killed The Goat

Earth faults can cause voltages to appear where you might not expect them.

If you make contact with two different voltages, current will flow through you. If the current is high enough and flows for long enough, it can cause your heart to go into ventricular fibrillation, which is usually fatal.

Let’s test your knowledge of earthing hazards. See if you can figure out what killed the goat.

Answers

Earth faults occur when electricity ‘escapes the wires’ and returns to a substation through the ground. Where electric current enters the ground, there is a build up of electrical ‘pressure’ that causes the soil to rise in voltage. This is called Earth Potential Rise (EPR). The same thing happens at the supply substation, where the soil and everything bonded to it rises in voltage. During the earth fault, the substation rises to an EPR of perhaps several hundred volts, while everything away from the substation stays closer to zero volts.

Earth faults can be caused by a range of things, including traffic accidents, wildlife and equipment damage, but a very common cause is storms. Trees leaning against or falling on powerlines can cause earth faults that can last for a second or more.

In the case of our goat, the farm is located right next to a zone substation. During the overnight storm, a falling tree knocked down a powerline some distance away, which caused an EPR at the substation.

Our farmer would often chain his goat(s) to the shared fence of the substation, particularly during bad weather when they might be distressed and run away. Like many substations, the fence was bonded to the earthing system and so, during the earth fault, it rose to a high voltage (EPR) along with everything else. However the goats metal chain also rose in voltage to the EPR. The ground away from the substation remained at zero volts. The conductive chain allowed a voltage to be transferred from one zone (the substation) to another (the farm). The goat contacted two voltages and current passed through it. This current interfered with the signals controlling the goat’s heart, causing it to stop beating properly.

When working in or around substations, it is critical that you make sure everything you are using stays within one zone. Make sure nothing crosses a boundary, and remember that the substation fence is usually bonded to the substation earthing system.

For more information about earthing hazards and risk mitigation, Safearth can provide additional training to you or your team. We occasionally run public training courses, but also customize training courses for particular businesses and sites. Contact us for more information.

The Full Video

This video is an excerpt from a larger Earthing Safety video produced by Safearth, which is available to purchase for your business. We wish to thank the following organisations for their valuable assistance:

  Application advice, access to sites, content review.

  Photography and videography, as well as production assistance.

Talk to us about producing an electrical safety video for your business.