The service phase of the electrical connection to a customer endpoint device located within a power distribution system is determined by various techniques. At the feeder level, the system may be programmed to induce momentary power interruptions, thereby causing missed zero crossings at the customer endpoint devices. The pattern of these interruptions is a controlled one, designed specifically to avoid causing noticeable disruption even to sensitive devices, but to be unusual enough that it is statistically unlikely to be naturally occurring. The monitoring of the zero crossing information is used to determine the phase of the service line to the customer endpoint devices.