This invention relates to the field of determining phase, particularly in power lines.
In the United States and elsewhere, most homes and many businesses are connected to a power grid which supplies two phase power on three lines. Each phase is a 180xc2x0 apart, and typically each phase provides 120 volts AC, and 240 volts between the two xe2x80x9chotxe2x80x9d lines.
In a typical household or small business, some receptacles provide 120 volts on one phase, and others 120 volts on the other phase. It is sometimes desirable to know whether receptacles are on the same or different phases. For instance, when data signals are communicated over a power line from one receptacle to another, it may be necessary to know if the receptacles are on the same power phase. In another application, capacitors are coupled across the power lines at receptacles to filter out unwanted high frequency signals in the power lines. In order to filter out signals in both phases of the power lines, it is necessary to know which receptacles are on the same or different phases.
As will be seen, the present invention provides a simple circuit for providing phase information.
An apparatus for determining the phase relationship between power signals on power lines is described. A first and a second plug are used for coupling to different power line outlets. A plurality of indicators are included on the apparatus. At least one of the indicators is coupled to a circuit to provide a signal to indicate when the phase difference between the power line signals at the first and second plugs are different. In one embodiment the first, second, and third indicator indicates the presence of power at the first and second plugs as well as the phase relationship. The indicators may be ordinary bulbs, such as neon bulbs.