Rough-size an energizer joule rating from fence miles, strand count, and weed/brush load so underpowered chargers are not guessing games.
Use this before buying a charger for perimeter or cross-fence: longer multi-wire fences and heavy vegetation demand more stored joules.
Rules of thumb vary by brand. This planner uses miles × strands × a load factor to suggest a minimum joule class — then read the manufacturer’s miles rating.
Wire-miles = miles × strands. Suggested joules ≈ wire-miles × load × species × 0.25 (planning constant for a modest shock on average installs).
wire_miles = miles × hot_strands
joules = wire_miles × load_factor × species_factor × 0.25
Output joules (what hits the fence) matter more than marketing “stored” joules — compare apples to apples on the box.
1.5 miles × 3 strands = 4.5 wire-miles. Typical grass (×1) for cattle (×1): 4.5 × 1 × 1 × 0.25 ≈ 1.1 J minimum class — round up and prefer a unit rated for your miles in weeds.
Assumptions: continuous steel/aluminum conductors with adequate grounding; planning constant is empirical, not a lab standard.
Limits: polywire/tape resistance, poor grounds, and shorts dominate real voltage. Not a substitute for brand mile charts.
Responsibility: follow electrical codes, warning signs, and local fence laws; test with a fence voltmeter.
Output (or release) joules better indicate fence punch. Ignore inflated stored-only claims when comparing.
Energizer grounding is critical — often three 6–8 ft rods spaced apart in moist soil. A weak ground mimics a weak charger.
Netting adds capacitance/load — use a higher load factor or a netting-rated energizer.