Agribusiness Risk Underwriters measures the effectiveness of the grounding mechanisms at the poultry house main breaker panels. A very effective grounding mechanism will measure with a very low ground resistance — conversely, a less effective grounding mechanism will measure with a higher resistance. A high ground resistance is one of several indicators of an increased risk of sustaining damage from lightning strikes and power surges.
According to the National Electric Code, the ground resistance of a breaker panel should measure at 25 ohms or less… but several leading poultry house experts believe 25 ohms is an unreasonable threshold for poultry houses. ARU recommends that the ground resistance of breaker panels be as low as is reasonably possible, depending on the circumstances of each poultry farm. (Local soil type and moisture content has great bearing on the ability to achieve a low ground resistance.) In any respect, ground resistance at breaker panels should always be below 100 ohms.
If your ground resistance is 100 ohms or higher, you should take immediate action. To reduce the breaker panel’s resistance to ground, typically a farm owner would install one or more additional ground rods, driven in the soil outside of the control room, under the roof drip line, in an area where moisture collects. (moist soil = better grounding). The ground rod should be connected to a heavy gauge solid wire with an acorn clamp or similar device. This wire should be run through the control room wall and connected to the breaker panel. The resistance to ground should be measured with a ground clamp meter or similar device; the resistance should ideally be 25 ohms or less.