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Power company contracts for indoor lines carrying 40 amps or more usually use a single-phase 3-wire power distribution system. A single-phase 3-wire connection pulls 3 power lines into a building and provides electricity at both 100 and 200 volts.



This method had become popular as household appliances that use high levels of electricity have increased, like microwaves, air conditioners and hot plates. Many of these high-power products are rated for 200 volts. A 3-line system also allows for 100 volt lines for regular appliances to be used without changing anything.


In a single-phase 3-wire system, both ends of the primary coil and the center of the secondary coil inside the transformer are tapped with lines, and those three lines are used to distribute electricity. The center tap is called the neutral conductor. There is a 100 volt difference between the neutral line and each hot line, and the hot lines carry a total of 200 volts, making it possible to use either 100 or 200 volts.




Contracts for 40 amps or more are required to have a single-phase 3-wire system, but it could be useful to check which type of wires are connected to your power meter.

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