Abstract: An interface circuit permits a customer who receives two-phase service from an electrical utility company to use power from an on-site source instead of or in addition to the utility company's power. Several embodiments are disclosed, in some of which the interface circuit automatically disconnects the utility company's power lines if the utility's power is lost and connects the on-site power source. The interface circuit may be installed in whole or in part in a meter collar which fits between an electric meter and the meter socket box that the meter would otherwise plug into.