Quick Answer
Electric fences need a minimum of 2,000 volts under load to deter cattle, and 4,000–5,000 volts for goats, sheep with wool, and predators. These measurements should be taken at the farthest point from the energizer using a digital voltmeter, not at the energizer terminal. Most operations should target 3,000–5,000 volts throughout the fence run.
Understanding Voltage Under Load
"Under load" means with the fence active and connected — not disconnected from the fence and tested at the energizer terminal. An energizer may show 7,000–8,000V unloaded but only 3,000–4,000V with the fence connected and drawing power. Additionally, voltage at the energizer is always higher than at the far end of the fence — test at the farthest point to know your actual working voltage.
Minimum Effective Voltages
These figures represent the minimum voltage required to reliably deter the animal, not an ideal operating target. Aim for 1,000–2,000V above these minimums as a safety margin for seasonal variation and fence degradation:
- Cattle: 2,000V minimum; target 3,500–4,500V
- Horses: 3,000V minimum; target 4,000–5,000V
- Sheep (shorn): 2,500V minimum; target 4,000V
- Sheep (woolly): 4,000V minimum; target 5,500–6,500V
- Goats: 4,000V minimum; target 5,000–6,000V
- Pigs: 2,000V minimum; target 3,500–4,000V
- Deer (deterrent): 3,000V minimum; target 5,000V
- Coyotes: 4,000V minimum; target 6,000V
What Causes Voltage to Drop
Every point of contact between the fence wire and any grounded object bleeds energy from the system. The main culprits: vegetation touching the wire (the biggest single factor), failed insulators allowing wire to contact posts, broken or spliced wire with poor connections, and inadequate grounding preventing the return circuit from completing. Address these in order — vegetation first, then insulators, then connections, then ground system.
Measuring Voltage Correctly
A neon tester (the simple stick-style tester) tells you the fence is "on" but doesn't give an accurate voltage reading. A digital fence voltmeter reads actual voltage under load and is essential for proper fence maintenance. Quality digital voltmeters cost $20–$50 and pay for themselves the first time they help you locate a voltage problem without walking the entire fence line.
Our Recommendation
Test voltage quarterly — spring, midsummer, early fall, and midwinter. Record the readings at 3–4 points along the fence. A steady decline over seasons indicates either vegetation growth, ground system degradation, or energizer output decline. Catching this trend early allows low-cost corrective action before the fence fails to contain livestock.