A transfer switch mountable in a standard electrical panel connects either a utility supply or an auxiliary supply to an electrical system. An internal mechanical interlock prevents both the utility supply and the auxiliary supply from simultaneously being connected to the system. The transfer switch may utilize either a rocker-style or a blade style switch. A light-emitting diode provides an indication of whether the utility supply is connected to and a voltage is present at the utility supply terminal. A power meter provides an indication of the magnitude of power drawn from the auxiliary supply when the auxiliary supply is connected to the load.