Full Definition
Three-phase power delivers electricity across three alternating conductors, each offset by a third of a cycle, so delivered power never drops to zero the way it does on single-phase. Motors above roughly 5–7.5 horsepower are almost exclusively manufactured in three-phase, which makes it mandatory for compressors, chillers, conveyors, presses, and commercial HVAC. Industrial services are quoted as voltage/amperage/phase — 277/480V three-phase is the modern standard, while 120/208V is common in older small-bay flex. Capacity is calculated as volts × amps × 1.732 ÷ 1,000 = kVA, with continuous load generally planned at 80% of the service rating.
Example
A 480V, 1,200A three-phase service delivers roughly 1,000 kVA, or about 800 kVA of continuous usable load. That comfortably serves a shell distribution warehouse but falls well short of a cold storage facility, which typically needs 2,000–4,000A.
Why It Matters
Undersized power is an obsolescence risk that hides in plain sight — the building looks fine. It disqualifies manufacturing, cold storage, and food processing tenants before the first tour, and upgrading commonly costs $50,000–$500,000+ with 12–24 month equipment lead times.