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What is the difference between single-phase and three-phase electric service?
Monday, January 27, 2020
Single phase electric service is what comes into virtually all homes. The service has two hot wires that are cycling through the same phase but in opposition, as shown in the diagram below. One leg produces 120-volt current and the two legs together produce 240-volt current because of the difference in the electrical potential between the two. It’s also worth noting that single-phase is a pulsating current, but three phase is not.
Three phase is the way power is generated and transported over long distances by electric utilities. It is also the type of service to large commercial and industrial buildings. Three phase is converted to single phase (split-phase) by residential transformers, primarily because single phase is more suitable for residential power requirements for lighting and small appliances.
The diagram below shows the wave pattern of each phase of one cycle of three phase power, with the vertical dimension being voltage and the horizontal representing time. Each phase is symmetrically 120º apart over a 360º cycle, and the elegance of this pattern is that it provides a continuously balanced flow of electricity, so that the sum of the three conductors is always zero. In other words, the voltage of one conductor at any point in time is balanced by the opposite voltage of the sum of the other two conductors.
Also, see our blog post “What is a reliable way to tell if the electric service is 3 phase or single phase?”
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