The Current That Comes in Threes [/ðə ˈkɑrənt ðət ˈkəmz ɪn ˈθriz/] n - Nearly everything in The Engines of the Hall is distributed as three-phase power: three AC voltages of the same magnitude offset by 120°. It is the substrate upon which the whole facility is built, which is why this entry is linked from nearly everywhere.

Why three phases

• More power per conductor. [/ˈmɒrɛ ˈpɒwɛr ˈpɛr ˈkɒndʌktɒr/] n Three phases deliver constant total power and do more work with less copper than the equivalent single-phase wiring; for this reason the Where the Grid Comes In and Busway distribution are three-phase.
• Smooth rotation. [/ˈsmʌːth ˈrɒtætɪɒn/] n Motors (in cooling plants) and the rectifiers within a Uninterruptible power supply run more smoothly on three phases.
• Balanced loading. [/ˈbælænkɛd ˈlɒædɪng/] n Single-phase server loads are spread across the three phases so that no single conductor is overloaded, a balancing the Rack power distribution unit and Power distribution unit are designed around.

Of wye and the two voltages

Low-voltage distribution is usually a wye configuration with a neutral, which yields two usable voltages at once: the higher line-to-line voltage between any two phases, and the lower line-to-neutral voltage for single-phase loads. That neutral, and its single bond to ground, is precisely the concern of the Grounding and bonding entry.

A The Standby Engine must synthesize this same balanced three-phase waveform, matching voltage, frequency, and phase, before an Automatic transfer switch will transfer the load onto it.

Part of The Engines of the Hall.