Electric Motors And Generators/Three-phase
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Electric Motors And Generators
[edit] Three Phase Alternating Current
In North America, three phase alternating current is generated and transmitted using three conductors to industry, commercial buildings and to a group of houses. Some older installations use 2400/4160Y three-phase systems, but most currently use 7200/12470Y. Near a group of houses is a step down transformer wired in a "Wye" or "Star" configuration. Each individual house receives two of these three phases along with a neutral conductor. The neutral conductor comes from the middle tap of the "Wye." Other houses receive different phases which are balanced throughout the group.
In a house, the breaker panel provides connections between the two phases and the neutral conductor. Most of the household outlets are connected between one of the "hot" phases and the neutral with a safety breaker permitting a maximum of 15 amperes. For the larger loads, such as the oven and the clothes dryer, the breaker panel connects across the two hot phases to provide 208 VAC, limited to a maximum of 40 amperes. The 208 VAC is √3 or 173% of the single-phase to neutral voltage.
