ANATOMY OF A RESIDENTIAL DISTRIBUTION SYSTEM

Most North American residences receive electricity from a unified grid; 60Hz three-phase power at various voltages is stepped down at local substations and, again, at pole- mounted or ground-level transformers. Each transformer feeds single-phase nominal 240V or 230V to one or more dwellings.

Large estates occasionally receive three-phase power or higher voltage, in which case there is a customer-owned transformer, but a three-wire, two-voltage setup is the norm. The secondary provides two hot legs from a grounded neutral centre tap. The local utility determines the service point, which is the boundary between its equipment and that of the customer. For an aerial service, this change in venue is often where the aerial triplex is spliced to the customer-owned service entrance cable. The splice is made by the utility just upstream from the weatherhead.

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