3 Phase Electric Wiring

Electricity generation in the United States is typically 3 phase generation at 60Hz, and that 3 phase power is used for long distance transmission of power and for high power industrial use. For household wiring it is usually supplied as 240 volt single phase with a center tap dividing it into two 120 volt supplies. While lighting, normal appliances, etc. are supplied with 120 volts AC, larger appliances may be supplied with 240 volts, single phase. Note that the labeled voltage is typically the rms value of the voltage, and that a 120 volt (rms) household circuit has a peak voltage of 170 volts.

Powering a three-part load, like three identical coils in a 3 phase motor, is a common application and provides an efficient use of 3 phase power. 为三相负载供电，例如三相电机中的三个相同线圈，是一种常见应用，能够高效利用三相电源。

The three coils of a 3 phase voltage source can be configured as a Wye (sometimes called Y or Star). If the coil voltage is 277V, then a connection to the ends of two adjacent coils would produce 480 volts. 三相电压源的三个线圈可以配置为星形（有时称为Y或星形）。如果线圈电压为277V，那么将两个相邻线圈的末端连接起来会产生480伏电压。

Such voltages from Wye configurations of 3 phase circuits are commonly encountered. If 120 volts is supplied to each supply coil of a Wye, the voltage obtained by bridging two coils is 208 volts. This is less than the 240 volts obtained from a single phase circuit with two 120 volt coils in series, but some equipment can be operated with either 208V or 240V. With the 208V for a given load, the supplied power is only 75% as large since it is proportional to the square of the voltage.

Three phase circuits can also be wired in the delta configuration (sometimes called mesh), where any two connections will give the coil voltage as an output voltage. 三相电路也可以以三角形（有时称为mesh）方式连接，其中任意两个连接都会产生线圈电压作为输出电压。

Advantages of 3 phase power distribution:

• For a balanced 3 phase supply, the total current is zero.
  • This minimizes magnetic fields surrounding the transmission lines.
    这最小化了传输线周围的磁场。
  • The three phases provide a naturally rotating magnetic field for three phase motors. This simplifies design and enhances efficiency.
    三个相为三相电机提供了自然旋转的磁场。这简化了设计并提高了效率。
  • When connected to large motors, it provides constant power and minimizes vibration. This leads to longer equipment life.
    当连接到大电机时，它提供恒定的功率并减少振动。这有助于延长设备的使用寿命。
  在三相平衡供电情况下，总电流为零。